Physiological disorders

1. Why Are Physiological Disorders So Common in Cauliflower?

Cauliflower is one of the most demanding and “finely tuned” vegetable crops. Its curd is not just a cluster of leaves or a fruit, but a complex structure composed of fused, undifferentiated shoots with flower primordia. The formation of this structure requires an ideal balance of external factors, and any imbalance immediately affects the appearance and quality of the harvest.

Here are the three main reasons why physiological disorders in cauliflower are so frequent:

2. Buttoning (Too Small Curd)

You eagerly await the harvest, fertilize, water, but instead of the promised large “rosette,” the cauliflower forms a tiny curd the size of a chicken egg or walnut. Such curds usually quickly become loose and start to flower without having time to gain mass. In agronomy, this condition is called “buttoning” (from the English “button” – a small bud or button).

Why does this happen?

The main cause of buttoning is premature curd initiation. The plant, for some reason, “decides” that it is time to move to flowering, even though it is still too small and has not had time to grow enough leaves. To form a large marketable curd, cauliflower needs a powerful leaf rosette—it is the leaves that supply carbohydrates for curd growth (Wien & Stützel, 2020; Rubatzky & Yamaguchi, 1997).

Scientists have established a clear pattern: the larger the leaf mass of the plant at the time of curd initiation, the larger the curd itself will be. If initiation occurs when the plant has only 5–10 small leaves, the curd will remain tiny (Wien & Stützel, 2020).

Main risk factors (when it happens most often):

1. Overgrown transplants. This is the most common cause. If the seedlings are too old (over 45–50 days) and large, especially if they have begun to stretch, they easily transition to the reproductive phase while still in the seedbed or immediately after transplanting. Once such a “mature” seedling is placed in cool soil or air, the curd initiation process starts instantly. The plant stops producing leaves and channels all its energy into forming a tiny curd. In Russian-language literature, this condition is often described as the cause of “loose” or underdeveloped curds (Autko et al., 2012).

2. Cold stress after transplanting. If you transplant seedlings into the open ground and then a sharp cold snap occurs (prolonged temperatures below +10 °C) or, worse, frosts, this becomes a powerful signal to shift to flowering. The plant “thinks” the growing season is ending and strives to produce offspring, even at the cost of a tiny curd (Wien & Stützel, 2020).

3. Nitrogen deficiency and other stresses. Drought, poor soil structure, root damage during transplanting, or lack of nitrogen slow down vegetative growth. If the plant is weakened and conditions become unfavorable, this can also trigger premature curd initiation.

How to avoid buttoning?

Unfortunately, once the process has started, the situation cannot be corrected – the small curd will remain small. Therefore, all efforts should be directed at prevention:

• Maintain the optimal age of transplants. For most varieties and hybrids, this is 35–45 days from emergence (Autko et al., 2012). Do not keep plants in trays or pots too long. Transplant them when they have 4–6 true leaves, but before they become overgrown.
• Choose the right planting dates. Transplant when the risk of severe return frosts has passed and the soil has warmed to at least +10…+12 °C. A sharp temperature drop is the main enemy.
• Choose resistant varieties and hybrids. Modern breeding offers varieties with a longer juvenile period – they “ignore” cooling for longer and manage to build a good leaf rosette before curd initiation. Pay attention to variety descriptions: labels like “resistant to buttoning” or “for early spring cultivation” are good signs.
• Give plants a comfortable start. Do not plant seedlings in unheated, cold, or dried-out soil. After transplanting, provide regular watering so roots establish quickly, and, if necessary, cover the plantings with non-woven fabric in case of sudden cold.
• Balanced nutrition. Do not forget about nitrogen at the initial stage – it is needed for leaf growth. But remember that excess nitrogen is also harmful (we will discuss this in later chapters). The main thing is that the plant does not starve in the first weeks after transplanting.

Remember the main point: a healthy, powerful rosette of 15–20 quality leaves is the key to a large and dense curd. If your seedlings are overgrown and the weather forecast predicts cold, it is better not to risk transplanting; instead, keep the plants in a cooler place to slow their growth, but avoid curd initiation.

3. Riciness (Loose, Grainy Curd)

Imagine: you have grown a beautiful rosette of leaves, the curd has begun to set, but instead of becoming dense and smooth, its surface looks like velvet or even fine grit – it seems to “crumble” into many tiny bumps. Such a curd loses marketable appearance, ages faster, and begins to flower. In professional circles, this condition is called “riciness” (from the English “rice,” due to its resemblance to rice grains) or “grittiness” (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

Why does this happen?

To understand riciness, we need to look at the biology of cauliflower. The curd is essentially a flower stalk that has been arrested in development. Under normal conditions, numerous flower primordia remain in an embryonic state and do not develop further. In riciness, this brake is released – and the flower primordia begin to grow prematurely (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

This disorder is directly related to temperature instability during the critical period of curd formation:

1. Cold start, then sharp warming. The classic scenario: during curd initiation, the weather was cool (optimal for initiation), and then suddenly warmth arrived (above +20 °C). The cold triggered the formation of flower primordia, and the subsequent warmth accelerated their growth but did not allow them to become part of a single dense structure. As a result, individual buds begin to protrude from the general mass, creating a grainy effect (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

2. Genetic predisposition. Different varieties respond differently to temperature fluctuations. Tropical and early varieties, which tend to flower quickly, are particularly prone to riciness. They seem to “wait” for the slightest warming to start forming flowers. Conversely, late varieties, which require prolonged vernalization, suffer from grittiness much less often (Rubatzky & Yamaguchi, 1997).

3. Uneven growth and excess nitrogen. If the curd grows too quickly – for example, due to abundant nitrogen fertilization or after rain in warm weather – this can also trigger accelerated development of individual flower buds. The internal processes within the curd become desynchronized, and some buds “break ahead.”

How to avoid riciness?

As with buttoning, the key strategy is minimizing stress and choosing the right cultivation practices:

Choose resistant varieties. When buying seeds, pay attention to varieties and hybrids resistant to riciness. This is especially important if you live in a region with unstable spring or autumn weather, where sharp temperature fluctuations are common. Late varieties tend to be more resistant to grittiness (Rubatzky & Yamaguchi, 1997).

Try to smooth out temperature conditions. This sounds nearly impossible in open ground, but several techniques work:

• Use row cover (spunbond, agrofabric) during cold periods to protect the curd from severe chilling.
• In hot weather, provide regular watering – this helps reduce heat stress.
• Choose planting dates so that the curd formation period falls during a more stable temperature window (for example, for an autumn harvest – late summer to early autumn, when there is no intense heat and no frost yet).

Control nitrogen nutrition. Nitrogen is necessary for leaf growth, but during curd formation and growth, it is better to reduce its amount. Excess nitrogen at this time stimulates rapid tissue growth, which may enhance the effect of uneven bud development. Prefer potassium-phosphorus fertilizers during the curd growth stage (Rubatzky & Yamaguchi, 1997).

Timely harvest. Do not keep curds on the bed too long. As soon as the curd reaches marketable size and density – cut it. With each day of delay, the risk of riciness and transition to flowering increases many times over.

Important note: slight grittiness may be acceptable for some varieties and is not considered a critical defect for home use. However, if you are growing cauliflower for sale or want a perfect harvest, riciness is a serious problem that is easier to prevent than to correct.

Now we know how to avoid a “grainy” curd. In the next chapter, we will consider the case where real leaves start growing inside the curd – leafy curd.

4. Leafy Curd (Leaves Inside the Curd)

Sometimes, when you cut open a formed cauliflower curd or even just look at it, you may notice small green leaves appearing among the flower buds (bumps). Sometimes they grow through the curd to the outside, making it “hairy” or “shaggy.” In agronomy, this phenomenon is called leafy curd (literally, “leafy head”) (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

Why does this happen?

Under normal conditions, leaf growth at the shoot tip is suppressed, and all the plant’s energy is directed toward forming the inflorescence – the curd. In leafy curd, this mechanism is disrupted: the apical meristem partially “reverts” to vegetative development, and instead of flower buds, leaf blades begin to form.

The main cause is stress from high temperatures at the time of curd initiation and early growth. This disorder is a typical response of the plant to overheating (Wien & Stützel, 2020).

When heat arrives (average daily temperature above +20…+22 °C, especially when the thermometer rises above +25 °C during the day), the curd formation process can go awry. Instead of setting flower buds, the meristem starts forming leaves – this is a kind of protective reaction, an attempt to increase the evaporative surface and cool down.

Additional factors that increase the risk:

• Genetic predisposition. Some varieties and hybrids are more prone to leafy curd, especially early and tropical ones, which are less stable at high temperatures. Resistance to this disorder is an important breeding trait (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).
• Excess nitrogen. Plants overfed with nitrogen tend to have excessive vegetative growth. Under heat stress, this tendency can be exacerbated, and the plant “chooses” the easier path – growing leaves instead of the complex inflorescence structure.

How to avoid leafy curd?

Since the main cause is heat, efforts should be directed at protecting plants from overheating during the critical period (curd initiation and early growth).

• Choose heat-resistant varieties and hybrids. This is the most reliable method. When buying seeds, look for labels such as “resistant to leaf formation in the curd,” “heat-tolerant,” “for summer cultivation.” Modern hybrids generally lack this problem (Rubatzky & Yamaguchi, 1997).
• Shift planting dates. If you live in a region with hot summers, try to have curd initiation and growth occur during cooler times – early spring or, often better, late summer to autumn. Autumn cauliflower suffers less from leafy curd because by the time the curd forms, the heat usually subsides.
• Provide adequate watering. Regular watering not only prevents drought but also helps cool plants through evaporation. Mulching the soil retains moisture and reduces the temperature of the root zone.
• Do not overfeed with nitrogen during curd initiation. Remember: nitrogen is for leaves; curds need potassium and phosphorus. Switch to potassium-phosphorus fertilizers when the curd is just beginning to set.

Important nuance: sometimes leafy curd may be minor and does not affect taste. But if there are many leaves, the curd becomes flabby, loses density, and marketable appearance. For home use, such cabbage can be cleaned of excess leaves, but for sale or processing it is already a defect.

Now we know how to avoid turning the curd into a “green bush.” In the next chapter, we will discuss a truly terrible disorder – blindness, when the plant simply loses its growing point.

5. Blindness (Absence of Growing Point)

One of the most unpleasant situations that can happen to cauliflower: you sow seeds, seedlings emerge, and then... nothing. The plant does not develop further, does not form new leaves, and instead of a top, it has a strange “platform” or scar. In agronomy, this condition is called blindness (from the English “blind” – without a growing point) (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

What is it and why does it happen?

Blindness is the death or underdevelopment of the apical meristem (growing point). Without it, the plant cannot form new leaves, much less a curd. Essentially, this is a disabled plant, doomed to die or to form ugly side shoots.

The causes of this disorder are not fully understood, but several main factors have been identified (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020; Startsev, 2021):

1. Low temperatures at an early age. This is the most frequently mentioned cause. If seedlings or very young plants (at the cotyledon or first true leaf stage) are exposed to frost or prolonged cooling (below +5 °C) – the growing point may die. Especially dangerous are combinations of low temperatures and lack of light (cloudy weather). In essence, the meristem simply “freezes” and dies (Wien & Stützel, 2020; Jonge et al., 2016).

2. Genetic predisposition. Some varieties and hybrids are more prone to blindness than others. Studies on broccoli (a close relative of cauliflower) have shown that sensitivity to cold varies greatly among varieties (Wien & Stützel, 2020). Unfortunately, seed labeling for resistance to blindness is rare, but if you know that this variety is prone to the problem – take precautions.

3. Mechanical damage. The simplest and most obvious cause – accidental damage to the growing point during weeding, pricking out, or transplanting. If the apical bud is broken or damaged, the plant becomes “blind.” Be careful when working with young plants!

4. Pest damage. Some pests specifically attack the growing point. For example, larvae of the cabbage stem weevil or the cabbage gall midge can damage the apical bud, leading to the death of the growing point and the formation of several small curds instead of one (Startsev, 2021).

5. Boron or molybdenum deficiency (less common). Although boron deficiency most often manifests as browning or hollow stem, in some cases it can lead to the death of the growing point (Rubatzky & Yamaguchi, 1997). This is more an exception, but possible under severe starvation on very poor soils.

How to avoid blindness?

Unfortunately, if the growing point has already died, it cannot be restored. The plant must be discarded. Therefore, the main strategy is prevention:

• Protect seedlings from cold. This is the most important! Do not sow seeds too early in cold soil. If frosts are forecast, be sure to cover the seedlings with agrofabric (spunbond, lutrasil). Pay attention to the quality of the cover – it should protect not only from frost but also from cold wind. For seedlings in a greenhouse or hotbed, monitor the temperature – do not allow prolonged cooling below +10…+12 °C (Rubatzky & Yamaguchi, 1997; Autko et al., 2012).
• Choose resistant varieties. If return frosts are common in your region, prefer more cold-tolerant varieties and hybrids. Pay attention to reviews from other gardeners and recommendations for your climate zone.
• Handle seedlings carefully. When pricking out, transplanting, and weeding, try not to damage the central growing point. Hold the seedling by the cotyledon leaf or the side of the stem, but not by the tip.
• Control pests. Regularly inspect seedlings. If you notice damage (curled leaves, bite marks, deformed top) – take action. Treat plants with approved insecticides in time or use row covers to protect from insects.
• Provide balanced nutrition. Although micronutrient deficiency is not the main cause of blindness, make sure your soil contains sufficient boron and molybdenum. Apply complex fertilizers with micronutrients or carry out foliar feeding (by leaf) with a solution of boric acid and ammonium molybdate for preventive purposes.

Signs of blindness:

• Seedlings stop growing and do not produce new leaves.
• The top of the plant looks like a flat “platform” without a visible bud.
• A scar or brownish spot (sign of tissue death) may appear at the tip.
• Some plants may develop side shoots, but they are usually weak and do not form a normal curd.

So, we have understood why cauliflower may completely lack a growing point. In the next chapter, we move on to another nutrition-related problem – whiptail, or molybdenum deficiency, when leaves become whip-like.

6. Whiptail (Molybdenum Deficiency)

If you see that the leaves of cauliflower have become narrow, deformed, resembling whips or straps, and the curd hardly develops – most likely, your plant is suffering from acute molybdenum deficiency. In agronomy, this condition is called whiptail (from the English “whip” – a whip, lash) (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

Why does this happen?

Molybdenum is a key micronutrient for cauliflower. It is a component of the enzyme nitrate reductase, which is responsible for converting nitrate nitrogen into ammonia form, necessary for protein synthesis. Without molybdenum, the plant cannot assimilate nitrogen, even if there is plenty of it in the soil (Rubatzky & Yamaguchi, 1997; Startsev, 2021).

With molybdenum deficiency, growth and tissue differentiation are disrupted – young growing leaves are particularly affected. Instead of a normal broad leaf blade, narrow, deformed strips of tissue are formed, and the main vein remains underdeveloped. The curd either does not set at all or forms a small, ugly one.

The main cause of whiptail is acidic soil pH. Molybdenum becomes available to plants only at pH above 6.0. In acidic soils (pH below 5.5), this element is firmly bound to soil particles and becomes unavailable to roots, even if it is present (Rubatzky & Yamaguchi, 1997; Autko et al., 2012).

Risk factors:

• Acidic soils (pH < 5.5). This is the main and almost only cause. In regions with acidic sod-podzolic soils, peat bogs, or with long-term use of acidic mineral fertilizers without liming, whiptail is especially common.
• Low molybdenum content in the soil. On very poor soils where molybdenum content is initially low, the problem can arise even at optimal pH.
• Intensive application of nitrogen fertilizers. With an excess of nitrate nitrogen, the plant’s need for molybdenum increases, which can provoke deficiency even on soils with borderline levels of the element.

How to recognize whiptail?

• Leaves become narrow and deformed. Young leaves grow abnormally: they are narrow, elongated, resembling straps or whips. Sometimes the leaf blade is underdeveloped, and veins remain thick and coarse.
• Leaf margins are curled. Leaves may curl downward or upward, becoming brittle.
• Curd does not form or is small. Instead of a dense curd, a loose, underdeveloped inflorescence or several small curds may form.
• Chlorosis between veins. Leaves may yellow between veins, but this symptom is nonspecific and not always present.
• General growth depression. The plant looks weakened, lags in growth, foliage is pale.

How to correct and prevent whiptail?

The good news: this disorder is relatively easy to prevent and correct if noticed in time.

1. Lime acidic soils. This is the most important and long-term method. Apply lime (dolomite flour, chalk, slaked lime) in advance, 2–3 months before planting, to raise soil pH to 6.0–6.5. This is optimal for cauliflower. Liming not only solves the molybdenum problem but also improves the uptake of other elements (Rubatzky & Yamaguchi, 1997; Autko et al., 2012). Recommended: check soil pH annually with a simple pH meter or test strips.

2. Apply molybdenum fertilizers. The quickest way to solve the problem is to feed plants with molybdenum.

• Soil application: you can add ammonium molybdate or sodium molybdate to the soil before planting. The dose is about 0.5–1 kg/ha of active ingredient, or about 0.5–1 g per 1 m² (for gardeners: roughly a teaspoon of ammonium molybdate per 10 m²). Important: molybdenum is applied to the soil only at pH > 6.0, otherwise it will still be unavailable (Rubatzky & Yamaguchi, 1997).
• Foliar feeding (by leaf): the most effective and fastest method when symptoms have already appeared. Spray the plants with a solution of ammonium molybdate (0.02–0.05% solution, i.e. 2–5 g per 10 L of water). Repeat after 7–10 days if necessary. This method works even on acidic soils because molybdenum enters directly into the tissues (Rubatzky & Yamaguchi, 1997).

3. Use complex fertilizers with micronutrients. With regular fertilization, prefer fertilizers that contain not only NPK but also a full range of micronutrients, including molybdenum.

4. Balanced nitrogen nutrition. Do not apply excessive doses of ammonium or nitrate nitrogen without controlling pH and the presence of micronutrients. Excess nitrogen increases the need for molybdenum.

Important note: if you already see typical whiptail symptoms – narrow, whip-like leaves – immediately carry out foliar feeding with molybdenum. Yield may be reduced, but you can save at least part of the plants. In subsequent seasons, be sure to lime the soil.

Interesting fact: whiptail is a classic “textbook” disorder often cited as an illustration of the importance of micronutrients. Cauliflower is an indicator crop for molybdenum deficiency: if it lacks molybdenum, it is immediately visible (Wien & Stützel, 2020).

Now we know how to recognize and treat molybdenum deficiency. In the next chapter, we will discuss another nutrition-related disorder – browning, or internal browning, caused by boron deficiency.

7. Browning (Internal Browning)

Sometimes, when you cut open a beautiful cauliflower curd from the outside, you find an unpleasant surprise inside: brown, rusty spots, areas of dead tissue that spoil the entire “rosette.” This condition, known as browning, is a classic symptom of acute boron deficiency (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

Why does this happen?

Boron is one of the most important micronutrients for cauliflower. It plays a key role in cell division, cell wall synthesis, carbohydrate transport, and growth of young tissues. The cauliflower curd is actively dividing and growing tissue, so it is particularly dependent on boron (Rubatzky & Yamaguchi, 1997).

With boron deficiency, the structure of cell walls is disrupted, especially in rapidly growing parts of the plant – young leaves, growing points, and, most importantly, the inflorescence. Cells become fragile, their walls break down, tissues die, and characteristic brown or rusty necrotic areas form in their place. They are most often localized in the stem, at the base of individual curd branches, or in the core of the curd itself (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020). Browning may sometimes be accompanied by hollow stem – two sides of the same problem (Autko et al., 2012).

Causes of boron deficiency:

• Low boron content in the soil. Many sandy, loamy sand, acidic sod-podzolic, and peat soils are initially low in boron (Rubatzky & Yamaguchi, 1997).
• Lack of moisture. Boron is a mobile element, but its uptake by the plant depends on water flow. In dry weather, even if boron is present in the soil, it may be unavailable to roots. Particularly dangerous is uneven moisture – “drought then flood” (Rubatzky & Yamaguchi, 1997).
• Excess calcium or magnesium. Application of large doses of lime or dolomite (without considering crop needs) can reduce boron availability to plants.
• Intensive growth. Rapid curd growth in favorable weather increases the plant's demand for boron. If this element does not come from the soil in sufficient quantities, deficiency occurs.

How to recognize browning?

• Brown or rusty spots on the curd. Spots may be small or cover a significant part of the inflorescence. Color ranges from light brown to dark rust.
• Browning in the stem core or at the base of branches. When cut open, brown areas, sometimes with cavities, are visible.
• Cracks on the stem. In severe cases, cracks may appear on the stem, sometimes with gum exudation. This is also a sign of severe boron starvation (Autko et al., 2012).
• The external appearance of the curd may remain normal. The insidiousness of browning is that from the outside the curd may look perfectly white and dense, and defects are only found when cut.

How to prevent and correct browning?

The main strategy is prevention, since it is impossible to correct already formed browning inside the curd.

1. Apply boron before planting or at the start of the growing season. The most reliable method is to apply boron fertilizers to the soil in advance, when preparing the bed. Recommended dose: 10–15 kg/ha of boron as active ingredient, or about 1–2 g per 1 m² (for gardeners: 1–2 g of boric acid per 1 m² – about ½–1 teaspoon per 1 m²) (Autko et al., 2012; Rubatzky & Yamaguchi, 1997). Important: boron is a micronutrient; its excess is toxic! Do not exceed the dosage. It is better to apply less than more.

2. Foliar boron applications. This is the fastest way to deliver boron to the plant at the first signs of deficiency. Spray the plants with a solution of boric acid (0.1–0.2%, i.e., 10–20 g per 10 L of water) at the curd formation stage (when the curd reaches 3–5 cm in diameter). Repeat after 7–10 days (Autko et al., 2012).

3. Ensure uniform watering. This is critically important! Boron enters the plant only with water. Keep the soil moist, but without waterlogging. Watering is especially important during curd formation and growth. Even a short drought can trigger boron deficiency (Rubatzky & Yamaguchi, 1997).

4. Monitor soil pH. The optimal pH for cauliflower is 6.0–6.5. With strong liming (pH > 7.0), boron availability may decrease. Lime the soil moderately, only based on agrochemical analysis.

5. Use complex fertilizers with micronutrients. With regular fertilization, prefer complex fertilizers that contain micronutrients in chelated form, including boron. They provide more uniform and stable nutrition.

What to do if browning has already appeared?

Unfortunately, if the curd has already formed and brown spots are visible inside, they cannot be fixed. Such cabbage can be eaten by carefully cutting out the affected areas, but it is no longer suitable for storage or sale. Your task is to prevent this next time, using the preventive measures described above.

Important note: do not confuse browning from boron deficiency with bacterial rots. In bacterial infection, tissues usually become watery, slimy, with an unpleasant odor. In boron deficiency, affected areas are dry, hard, and odorless (Startsev, 2021).

So, we have learned how to recognize and prevent internal browning associated with boron deficiency. In the next chapter, we will examine a related disorder – hollow stem, which often arises from the same causes.

8. Hollow Stem (Hollow Stem)

Sometimes, when cutting off the cauliflower curd, you find that inside the stem, directly under the curd, a void has formed – a cavity. Externally, the stem may look perfectly healthy, but on cutting, a cavity is visible, sometimes with brownish edges or cracks. This condition is called hollow stem and is one of the common physiological disorders (Wien & Stützel, 2020; Rubatzky & Yamaguchi, 1997).

What is it and why does it happen?

Hollow stem is a mechanical breakdown of tissues inside the stem due to excessively rapid growth. The cells of the inner part of the stem (pith) do not have time to “mature” and strengthen while the outer tissues continue to actively grow and stretch. As a result, the inner tissue tears, forming a cavity or cracks (Wien & Stützel, 2020; Boersma et al., 2013).

It is important to understand: hollow stem is primarily a consequence of overly intensive growth, rather than simply a deficiency of a single element (Wien & Stützel, 2020).

Factors that provoke hollow stem:

1. Excess nitrogen and rapid growth. This is the main cause. If you overfeed plants with nitrogen (especially in easily available form – nitrate), they start growing very quickly. The stem elongates and thickens at a tremendous rate; internal tissues do not have time to strengthen, and tears form. The faster the plant grows, the higher the risk of hollow stem (Wien & Stützel, 2020; Hipp, 1974). Studies have shown that the shorter the period from sowing to maturity (i.e., the faster the plant grows), the higher the probability of hollow stem (Wien & Stützel, 2020).

2. Wide spacing (sparse planting). When plants are spaced far apart, each has more space, light, and nutrients. This stimulates faster growth, thus increasing the risk of hollow stem. In dense plantings, plants compete with each other, grow slower, and hollow stem occurs less often (Wien & Stützel, 2020; Zink, 1968).

3. Warm weather. High temperatures (especially combined with good humidity) accelerate growth. The warmer it is, the faster the plant accumulates biomass, and the higher the risk of cavity formation (Wien & Stützel, 2020).

4. Boron deficiency (as an additional factor). Lack of boron makes cell walls more fragile and weak. This is not the primary cause of hollow stem, but it can exacerbate the problem: cells weakened by boron deficiency tear more easily during rapid growth (Rubatzky & Yamaguchi, 1997). Therefore, hollow stem and browning often occur together.

5. Excess moisture and potassium deficiency. Abundant watering combined with potassium deficiency can also contribute to excessively rapid growth and weakening of tissues.

How to recognize hollow stem?

• External signs: the stem under the curd looks normal, thickened, without visible damage. Often the only way to detect the problem is to cut the stem.
• When cut: a cavity is visible inside the stem. The cavity may be small or occupy a significant part of the stem, sometimes with cracks.
• Sometimes: with severe hollow stem, the stem may have external cracks, especially at the base of the curd.

How to prevent hollow stem?

Since this problem is related to overly rapid growth, prevention lies in controlling the plant's growth rate:

1. Control nitrogen nutrition. Do not overfeed cauliflower with nitrogen, especially during stem formation and growth. Apply nitrogen fertilizers in split, small doses, preferring nitrate forms (less stimulating to rapid growth than ammonium forms). During active curd and stem growth, it is better to switch to potassium-phosphorus fertilizers (Autko et al., 2012; Rubatzky & Yamaguchi, 1997).

2. Moderate planting density. Do not plant too sparsely. The optimal scheme for most varieties and hybrids is 50–70 cm between rows and 30–40 cm in the row. If planted more sparsely (e.g., 70×50 cm), the risk of hollow stem increases. For home gardens: plant no more than 40 cm between plants in the row (Wien & Stützel, 2020).

3. Balanced nutrition. Besides nitrogen, ensure plants receive enough potassium. Potassium strengthens cell walls and makes tissues more resistant to tearing. Use complex fertilizers with an NPK ratio close to 1:1:1 or with a predominance of potassium during curd growth.

4. Apply boron. Although boron is not the main cause of hollow stem, its presence in the soil makes tissues stronger. Apply boron to the soil when preparing the bed (1–2 g of boric acid per 1 m²) or carry out foliar feeding at the beginning of curd formation (0.1–0.2% boric acid solution) (Rubatzky & Yamaguchi, 1997).

5. Control watering. Avoid sharp fluctuations in moisture. Water evenly, avoiding both drying out and waterlogging. Uniform watering is especially important during the period of rapid plant growth.

Does hollow stem affect yield?

Usually, hollow stem does not affect curd weight, but it can become a problem during storage. Through the cavity in the stem, pathogens can enter, and the cabbage will store less well. In addition, this disorder reduces the marketable appearance of the product – especially if you sell whole cabbage or in cuts. A sign that hollow stem may be related to excess nitrogen and other stresses, not to disease.

Table: Comparison of Browning and Hollow Stem

Now we know why the stem becomes hollow and how to avoid it. In the next chapter, we will examine why the curd may acquire a purple tint – a phenomenon most often associated with cold response and anthocyanin accumulation.

9. Purple Curd (Purple Tint of the Curd)

Sometimes, to the gardener's surprise, the cauliflower curd instead of the traditional white or cream color acquires a purple, lilac, or magenta hue. In some cases, it looks like a light bloom on the bumps of the inflorescence; in others, the curd becomes intensely purple, almost like ornamental varieties. This condition is called purple curd (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

Why does this happen?

The purple pigment that appears on the curd is anthocyanin – a natural plant pigment from the flavonoid group. Anthocyanins serve a protective function in plants: they act as a “sunscreen” and as an “antifreeze,” protecting tissues from ultraviolet radiation and cold damage (Rubatzky & Yamaguchi, 1997).

In cauliflower, the appearance of a purple tint is usually a response to cold. When the plant is exposed to low positive temperatures (around +2…+8 °C) or light frosts, it begins to actively synthesize anthocyanins to protect cells from damage. This mechanism is especially often triggered if cold occurs during curd growth (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

Main causes of purple tint:

1. Low temperatures (cold). The most common cause. If during curd formation and growth, night temperatures drop below +10 °C, and especially if frosts occur, the plant activates its protective mechanism and begins to produce anthocyanin. The colder it is, the more intense the purple color (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

2. Varietal characteristics (genetics). This is very important! Some varieties and hybrids have a genetic predisposition to accumulate anthocyanins. In some varieties, a purple tint appears at the slightest cooling, in others only under severe stress, and in still others, it does not appear at all (Rubatzky & Yamaguchi, 1997).

Important: there are special cauliflower varieties with purple curds – this is not a disorder but a varietal trait (e.g., varieties ‘Graffiti’, ‘Purple Cape’, ‘Violet Queen’). Such varieties are bred specifically for the market, and purple coloring is normal for them, not a defect.

3. Other stresses (rarely). Sometimes a purple tint may appear with phosphorus deficiency or in response to other stress factors (drought, sharp temperature fluctuations), but this is less typical.

How to tell if this is a disorder rather than a varietal trait?

• If you planted a white variety or hybrid, and the curd turned purple – this is a physiological response to cold (or, rarely, another stress).
• If you planted a purple variety (e.g., ‘Graffiti’), then purple coloring is normal, and there is no need to worry.
• Appearance: in response to cold, the purple tint is often uneven – some bumps may be purple, others white or with a light bloom. In a varietal trait, the color is usually more uniform and intense.

How to prevent purple tint? (if it is undesirable)

If you want to grow a classic white curd, take measures to protect against cold:

1. Choose correct planting dates. Try to have the curd formation period fall at a time when night temperatures are consistently above +10 °C. In regions with cold nights, it is better to grow cauliflower in summer or autumn (when temperatures are more stable) rather than early spring (Rubatzky & Yamaguchi, 1997).

2. Cover plants against cold. If frosts or severe cold are forecast, cover the plantings with agrofabric (spunbond, lutrasil). This will protect not only from frost but also from cold winds that intensify stress (Autko et al., 2012; Rubatzky & Yamaguchi, 1997).

3. Choose varieties resistant to reddening. When buying seeds, pay attention to labels: “resistant to purple tint,” “cold-tolerant,” “for early cultivation.” For regions with cool climates, such varieties are the best choice.

4. Ensure balanced phosphorus nutrition. Although cold is the main cause, sometimes phosphorus deficiency can enhance anthocyanin expression. Make sure the soil has enough phosphorus (especially if the soil is acidic or cold – phosphorus is poorly absorbed).

5. Avoid other stresses. Regular watering, wind protection, and proper nutrition will help the plant better withstand temperature fluctuations.

Does purple tint affect taste and nutritional value?

No! Purple tint does not affect the taste, texture, or nutritional value of the curd. Anthocyanins are beneficial antioxidants, so such cabbage may even be healthier than white. If aesthetics are important to you, you can carefully trim the purple areas, but they are also edible (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

What to do if purple tint has already appeared?

• If the color appeared after frost, but the curd is dense and healthy – simply harvest it and use it for food (taste will not suffer).
• If you want to preserve white color, you can try to protect the curd from further cooling, but it will not be possible to return to white; the pigment will remain.
• Note that purple tint may intensify during cooking – this is normal and safe.

Table: Purple Tint – Disorder or Normal?

So, we have learned that purple tint is most often a response to cold that does not affect taste and quality. In the next chapter, we will discuss another color-related problem – yellowing of the curd, which arises from exposure to sunlight and lack of blanching.

10. Yellowing (Yellowing of the Curd)

A snow-white, dense curd is the quality standard for cauliflower. But if left unprotected, it quickly loses its white color, becoming creamy and then bright yellow. Sometimes yellowing is accompanied by a pinkish or purple tint. This condition is called yellowing and is a classic example of a physiological disorder caused by external factors (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

Why does this happen?

The white color of cauliflower curd is the result of the absence of chlorophyll in the inflorescence tissues. When the curd is protected from sunlight (naturally covered by leaves), photosynthesis does not start, and chlorophyll is not formed. Once the curd is exposed to light, it begins to “green” or “yellow” – production of chlorophyll and other pigments (carotenoids) that give a yellow tint is activated. This is a protective response of the plant to ultraviolet radiation (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

In essence, yellowing is a natural aging and oxidation process, accelerated by sunlight. As the curd ages, it also yellows, but light significantly speeds up this process.

Main causes of yellowing:

1. Exposure to sunlight (lack of blanching). The most common cause. If the curd is not covered by leaves, it receives direct sunlight. This triggers the formation of chlorophyll and carotenoids, and the white color changes to yellow, and sometimes greenish (Rubatzky & Yamaguchi, 1997; Autko et al., 2012).

2. Lack of blanching (artificial shading). In commercial cultivation and home gardens, blanching is often practiced – shading the curd by tying or breaking inner leaves so that they cover the inflorescence from the sun. If this is not done, the curd will inevitably yellow (Rubatzky & Yamaguchi, 1997; Autko et al., 2012).

3. Aging of the curd (over-maturity). Even with good blanching, if the curd is not cut in time, it begins to age. Tissues lose elasticity, become loose, and simultaneously yellow pigments accumulate. This is a natural process associated with preparation for flowering (Wien & Stützel, 2020).

4. Varietal characteristics. Some varieties and hybrids are more prone to yellowing, others are more resistant. Modern hybrids generally have good self-blanching ability (their leaves tightly cover the curd) and retain white color longer (Rubatzky & Yamaguchi, 1997).

5. High temperatures and dry air. In hot weather, aging and oxidation processes accelerate, so yellowing occurs faster.

How to recognize yellowing?

• Color change: the curd becomes creamy, then yellow. Sometimes pinkish or greenish spots appear.
• Loss of density: yellowing is often accompanied by loss of firmness; the curd becomes looser.
• Appearance of “flower” buds: with severe aging, small green buds may appear on the surface of the curd – signs of the onset of flowering.

How to prevent yellowing?

The main strategy is to protect the curd from sunlight and timely harvest.

1. Blanching (shading). This is a mandatory agronomic practice for white varieties.

• When: when the curd reaches 3–5 cm in diameter (size of a walnut).
• How: carefully break or tie a few inner leaves over the curd so that they create shade. You can use soft twine, an elastic band, or simply break leaves so that they fall over the curd (Rubatzky & Yamaguchi, 1997; Autko et al., 2012).

Important: do not blanch colored-curd varieties (purple, orange, green) – they, on the contrary, need sunlight to develop pigmentation (Wien & Stützel, 2020). Also, do not blanch if intense heat is expected – this may provoke rot.

2. Choose self-blanching varieties and hybrids. Many modern hybrids have a dense leaf rosette that naturally covers the curd. This significantly simplifies care. Pay attention to variety descriptions: “self-blanching,” “with good leaf cover” (Rubatzky & Yamaguchi, 1997).

3. Timely harvest. Do not keep curds on the bed too long. Cut them as soon as they reach marketable size and density. Usually this period lasts only 5–10 days. Regularly inspect plantings to not miss the moment.

4. Optimal planting dates. Grow cauliflower during seasons when solar activity is not maximal (spring, autumn) or in regions with mild climates. In hot summer, yellowing occurs faster.

5. Moderate watering. Lack of moisture accelerates tissue aging. Keep soil moist but without waterlogging.

What to do if the curd has already yellowed?

Unfortunately, white color cannot be restored. However, a yellow curd is perfectly edible – it is not poisonous, although it may be slightly coarser and less tender in taste.

• Use it immediately – such cabbage stores less well.
• During cooking, yellow color may intensify, but this is normal.
• If yellowing is minor, you can trim the top layer, under which there may be white parts, but this is not always effective.

Important distinction: yellowing from aging and yellowing from bacterial rot are different things. In rot, tissues become slimy, watery, with an unpleasant odor. In physiological yellowing, the curd remains dry and dense (Startsev, 2021).

Table: Comparison of Yellowing and Other Color Disorders

So, we have learned how to protect the curd from sunlight and preserve its snow-white color. In the next, final chapter, we will consider heat stress – how heat affects the curd and how to avoid its crumbling and premature flowering.

11. Heat Injury (Heat Stress: Crumbling, Looseness, and Premature Flowering)

We have already mentioned that cauliflower likes cool weather but does not tolerate frost. However, heat is no less dangerous. If the thermometer stays above +25…+28 °C for an extended period, especially if heat is accompanied by dry air and lack of soil moisture, the plant experiences severe stress. The consequences of heat stress manifest in various ways, but all lead to loss of crop quality (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

How does heat affect cauliflower?

Heat stress disrupts several key processes at once:

1. Disruption of curd initiation and growth. Cauliflower curd forms only within a specific temperature range. At temperatures above +20…+22 °C, the inflorescence initiation process may stop or go wrong. Instead of a dense structure, individual shoots begin to grow actively, and the curd becomes loose, “ruffled” (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

2. Accelerated aging and transition to flowering. In heat, the plant “thinks” the growing season is ending and strives to produce offspring as quickly as possible. Instead of building a dense curd, it begins to form flower buds and elongate stems. This leads to premature flowering – the curd becomes “hairy,” green or yellow buds appear on it, it loses density and nutritional value (Wien & Stützel, 2020; Rubatzky & Yamaguchi, 1997).

3. Moisture loss (dehydration). In heat, evaporation from leaf surfaces and the curd increases sharply. If watering is insufficient, tissues lose turgor, become limp, and the curd becomes flabby, “cottony.” This is especially critical during the active curd filling stage (Wien & Stützel, 2020).

Main symptoms of heat stress:

1. Loosening of the curd (loose curd). The curd becomes loose, not dense; individual branches easily separate from each other. Instead of a compact structure, it resembles a “panicle” or “flower.” This is especially characteristic of early varieties and hybrids with a short curd formation period (Wien & Stützel, 2020).

2. Premature flowering (early bolting). On the surface of the curd or between branches, small green or yellow buds appear. The curd seems to “shoot” upward, turning into a flower stalk. Such cabbage is no longer suitable for consumption – it becomes coarse and bitter (Rubatzky & Yamaguchi, 1997).

3. Loss of density (soft, “cottony” curd). Even if flowering has not yet started, the curd loses firmness. It becomes soft, easily deformed when pressed. This is due to breakdown of cell walls from dehydration and heat stress (Wien & Stützel, 2020).

4. Leafy curd – as a consequence of heat. We have already discussed leafy curd in Chapter 4, but it is worth repeating: heat is one of the main causes of leaves inside the curd. The plant tries to increase evaporative surface by growing leaves instead of inflorescence (Wien & Stützel, 2020).

How to protect cauliflower from heat?

Although we cannot control the weather, we can mitigate the effects of heat stress with proper agronomic practices:

1. Choose heat-resistant varieties and hybrids. This is the most effective method. Modern breeding offers varieties and hybrids that can form a dense curd even at temperatures up to +25…+28 °C. Pay attention to labels: “heat-tolerant,” “summer,” “for warm climates.” Tropical and subtropical varieties (e.g., Indian and Chinese hybrids) are especially good for hot regions (Rubatzky & Yamaguchi, 1997; Wien & Stützel, 2020).

2. Shift planting dates to autumn. In regions with hot summers, the optimal time for cauliflower is not spring, but late summer to early autumn. Planted in July or early August, the cabbage forms its curd in September–October, when heat subsides and nights become cool. This guarantees a dense, snow-white curd (Rubatzky & Yamaguchi, 1997; Autko et al., 2012).

3. Provide regular and abundant watering. In hot weather, water cauliflower at least 2–3 times a week, and in extreme heat – daily, preferably by sprinkling or drip irrigation. Moisture not only nourishes the plant but also cools the soil and air around it. Important: water only in the morning or evening to avoid leaf burns from sunlight refracted in water droplets (Rubatzky & Yamaguchi, 1997).

4. Mulch the soil. A layer of mulch (straw, mown grass, compost) retains soil moisture, prevents overheating of the root system, and reduces evaporation. Mulch is especially effective when combined with drip irrigation (Autko et al., 2012).

5. Shade the plants. In intense heat, use shading nets (agrofabric) or simply throw thin non-woven material (spunbond) over the plantings. This lowers the temperature around plants by 3–5 °C and protects from direct sunlight. You can also plant cauliflower in partial shade of tall crops (e.g., corn or sunflowers) that create natural shade (Rubatzky & Yamaguchi, 1997).

6. Proper nutrition. In heat, avoid excessive nitrogen doses, which stimulate rapid growth and make tissues looser. Prefer potassium-phosphorus fertilizers, which strengthen cell walls and increase stress tolerance. Potassium is especially important for maintaining water balance (Rubatzky & Yamaguchi, 1997).

7. Timely harvest. In heat, curds grow very quickly, but they also overripen faster. Do not keep them on the bed too long – cut when they reach marketable size (usually 7–10 days after the start of formation). In heat, check plantings daily.

What to do if heat has already arrived and the curd is beginning to form?

• Increase watering. Increase frequency and volume of watering.
• Shade the curds. If possible, create temporary shade with netting or fabric.
• Cut the curd early. Even if it has not reached maximum size, it is better to cut it slightly earlier than to let it overripen and lose quality. A small but dense curd is better than a large but loose one.
• Use “rescue” varieties. If you live in a region with unpredictable climate, always keep seeds of several varieties – early (for spring), heat-tolerant (for summer), and late (for autumn). This way you can always hedge your bets.

Table: Summary of Physiological Disorders of Cauliflower

Conclusion

Cauliflower is a capricious but rewarding crop. Understanding the physiological processes occurring in the plant and the ability to recognize signs of stress in time is the key to success. Most problems can be avoided by choosing the right variety, adhering to planting dates, and providing optimal conditions: moderate temperatures, regular watering, and balanced nutrition.

Remember: your main task is to minimize stress factors that disrupt curd formation. Then your cauliflower will reward you with dense, snow-white, and delicious curds that will delight you and your family.

Good luck in your garden!

References

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2. Kemble, J.M., Bertucci, M.B., Jennings, K.M., Meadows, I.M., Rodrigues, C., Walgenbach, J.F., Wszelaki, A.L. (2022). Southeast U.S. Vegetable Crop Handbook. 23rd edition : Great American Media Services.
3. Schuh, M., MacKenzie, J. (2022). Growing cauliflower in home gardens. University of Minnesota Extension. Available at: https://extension.umn.edu/vegetables/growing-cauliflower. (Accessed: 5 July 2026).
4. Wien, H.C., Stützel, H. (2020). ‘Cauliflower, broccoli, cabbage, and Brussels sprouts.’, in The physiology of vegetable crops. UK: CABI, 357-388.
5. Аутко, А.А. (2012). ‘Современные технологии выращивания овощных культур [Modern technologies for growing vegetable crops]’, in Современные технологии в овощеводстве [Modern technologies in vegetable growing]. Минск, Белоруссия: Беларус. навука, pp. 93-347.
6. Старцев, В.И. (2021). ‘Наиболее распространенные болезни и вредители капусты [The most common diseases and pests of cabbage]’, in Овощеводство. Агротехника капусты [Vegetable growing. Cabbage cultivation techniques]. Москва: ИНФРА-М, pp. 73-90.