Growing Seedlings

When direct sowing can be successful

1. Regions with a long and cool growing season

In northern latitudes (e.g., Scandinavia, northern US states, Canada, Siberia), summers are short but can be quite cool and humid. Under such conditions, direct sowing of early varieties (with a growing period of 50–60 days) in late May – early June allows the plants to complete the entire cycle before autumn frosts, avoiding the transplanting stage (Rubatzky & Yamaguchi, 1997). However, even there this method is less reliable than seedlings and is often used only for the earliest hybrids.

2. Autumn harvest in regions with hot summers

In regions with temperate or continental climates, where summer temperatures are high, direct sowing of cauliflower is often practised in mid‑summer (July) to obtain an autumn harvest (UMN Extension, 2022). This approach works because:

• Seeds are sown when the soil is well warmed (above 18 °C), ensuring quick and uniform emergence.
• The head‑formation period falls in late August – September, when daytime temperatures drop to the optimal 15–20 °C.
• The plants have time to develop a strong leaf rosette before cold weather sets in.

This method is especially popular in the US Midwest and the European part of Russia for obtaining a late harvest intended for storage (Startsеv, 2021).

3. Subtropics and regions with mild winters

In areas with mild winters (southern US, Mediterranean, Transcaucasia), direct sowing can be used to produce a winter harvest. Seeds are sown in late summer – early autumn so that plants develop during the cool period and form heads in winter or early spring (Kemble et al., 2022). In such conditions, the seedling method is often unnecessary because the climate itself provides the required temperature regime.

4. Use of special varieties

Some modern cauliflower hybrids are bred specifically for direct sowing. They feature:

• Accelerated growth rates in early stages.
• Tolerance to heat stress.
• Ability to form heads without strict dependence on day length.

Examples of such hybrids can often be found in seed catalogues for regions with short summers.

Limitations and risks of direct sowing

Even in the cases listed above, direct sowing is fraught with serious problems:

1. Difficulty controlling the "temperature window". You cannot manage the weather. If after emergence a week of heat (above 28 °C) or, conversely, frosts occurs, this can trigger buttoning (formation of small, underdeveloped heads) or a complete failure of curd initiation. With the seedling method, you can adjust transplant dates according to the forecast.

2. Vulnerability of seedlings. In open ground, young plants are easily destroyed by:

• Flea beetles (Phyllotreta spp.) – active in dry and warm weather, their attack at the cotyledon stage often kills seedlings (Swiader & Ware, 1992).
• Cabbage root flies (Delia radicum), which lay eggs at the base of the stem, and larvae damage the root system.
• Wind and rain, which can batter tender sprouts.

3. Uneven emergence. Cauliflower seeds are small and difficult to sow with perfect uniformity. As a result, some plants may be shaded by neighbours, leading to uneven harvest quality.

4. Loss of precious time. If direct sowing fails (e.g., due to drought or pests), you may not have time to resow in the same season. Seedlings are always ready to replace lost plants.

When direct sowing is not recommended

• In regions with short and unstable summers (northern territories, mountainous areas). Here the seedling method is almost mandatory.
• When growing late‑maturing varieties – they simply will not ripen with direct sowing.
• On heavy clay soils – they warm up slowly, and seedlings may rot.
• In areas with high pest pressure – if you cannot protect young plants with nets or row covers.

Practical recommendations for direct sowing

If you still decide to try direct sowing, follow these rules to reduce risks:

• Choose the earliest or mid‑early varieties with a growing season of no more than 70–80 days.
• Prepare the seedbed thoroughly – soil should be fine‑crumbly, moist, and warm (at least 12 °C at 5 cm depth).
• Sow seeds shallowly – at 1–1.5 cm, and firm the soil for good seed‑to‑soil contact.
• Use row covers (non‑woven fabric, agrofabric) for the first 2–3 weeks to protect against pests and sudden temperature changes.
• Provide regular watering – drying of the topsoil is deadly for small seeds.
• Thin when 2–3 true leaves appear, leaving 40–50 cm between plants (for early varieties – 30–40 cm).

Remember: even under ideal conditions, direct sowing of cauliflower always gives greater variation in maturity dates and head quality compared to the seedling method. For stable, high‑marketable yields, especially for sale, seedlings remain the gold standard (Kemble et al., 2022).

Why are sowing dates critical for cauliflower?

Cauliflower goes through several distinct development phases, each requiring specific temperatures:

1. From sowing to emergence – optimal 18–22 °C.

2. From emergence to the 4–5 true‑leaf stage – moderate temperatures (15–18 °C day, 8–10 °C night) and good light are preferred. During this period, the potential for the future harvest is laid down.

3. Formation of the leaf rosette – the plant builds vegetative mass. Moderate warmth (18–20 °C) accelerates growth.

4. Initiation and growth of the curd – the most critical phase. Optimal range: 15–18 °C day and 8–10 °C night (Startsеv, 2021). Above 20 °C, head quality declines sharply; above 25 °C, curd initiation may not occur at all (Rubatzky & Yamaguchi, 1997).

Thus, the sowing strategy is designed so that the curd initiation and growth phase falls during the period with the most favourable temperatures. For most temperate regions, this is late summer – early autumn (August‑September) or early spring if summers are not too hot.

Option 1. Early spring cycle (for early summer harvest)

This cycle suits regions with temperate climates where spring comes early and summers are not too hot, or for protected cultivation (greenhouses).

When to sow:

Sow in late February – March (depending on latitude) so that by transplanting (April‑May) the plants are 40–50 days old and have 4–5 true leaves. In warmer regions (southern Russia, southern US) you can shift sowing to January‑February.

How to calculate:

Determine the date when the average daily soil temperature at 10 cm depth reaches 8–10 °C and the risk of severe frosts has passed. Subtract 40–50 days from that date – that is your sowing date.

Variety selection:

Use exclusively early‑maturing hybrids with a growing period of 50–60 days from transplanting to technical maturity. Examples: 'Snowball', 'Rannyaya Gribovskaya', 'Alfa', 'Fremont' (for the US) (Kemble et al., 2022).

Risks:

The main danger is return frosts that can damage transplanted seedlings, or a sudden warm spell in May that causes rapid loosening of the head instead of filling. Therefore, the early cycle is reliable only in regions with cool springs or when using covers.

Option 2. Summer (autumn) cycle – the most reliable in temperate climates

This is the main and most recommended method for most regions with continental and temperate climates (European Russia, US Midwest, Canada, Northern Europe). The main goal here is to obtain a harvest in September‑October, when the heat subsides.

When to sow:

Sow in late May – early June so that seedlings are ready for transplanting in late June – early July. By then, the soil is well warmed, plants quickly start growing, and the main curd‑formation phase falls in August‑September (UMN Extension, 2022; Startsеv, 2021).

Calculation details:

• Seedling age at transplanting – 30–40 days (in summer culture, seedlings grow faster due to heat and light).
• Transplanting into the ground – when soil is warmed to 15–18 °C, usually in late June.
• Curd initiation occurs when plants reach 20–25 leaves (about 50–60 days after transplanting). For most varieties, this falls in mid‑August, when night temperatures already drop below 15 °C.
• Harvest – 70–90 days after transplanting, i.e., in September‑October.

Variety selection:

Choose mid‑early and mid‑season varieties and hybrids with a growing period of 70–90 days. Popular are 'Snow Crown', 'Cassius', 'Quarter', 'Parizhanka' (for Europe) (UMN Extension, 2022; Rubatzky & Yamaguchi, 1997).

Advantages:

• Minimal risk of heat stress during curd initiation.
• Autumn cooling improves flavour and increases curd density.
• Harvest stores well.

Important: in regions with very short summers (northern latitudes) move dates one to two weeks earlier, but use only ultra‑early hybrids.

Option 3. Winter cycle (for mild‑winter regions)

In subtropical and Mediterranean regions, as well as southern US and Transcaucasia, sowing in late summer – early autumn (August‑September) is practised to obtain a harvest in winter or early spring. Seedlings are grown in open ground (or cold frames) and transplanted to a permanent site in September‑October. During winter, plants continue to grow slowly, and heads form in February‑March when temperatures are optimal (10–18 °C) (Kemble et al., 2022).

Variety selection:

For this cycle, there are special winter‑hardy varieties (e.g., 'Roscoff', 'Saint‑Malo') that require vernalisation (cold exposure) for head initiation. They are later‑maturing and have a growing period of up to 200 days (Rubatzky & Yamaguchi, 1997).

General rules for any timing

Regardless of the chosen cycle, follow these simple rules:

• Base your timing on the variety, not the calendar – each variety has a recommended seedling age and sowing date indicated on the package. Use that as a basis.
• Consider your local climate – each location has its own "windows" for transplanting. It is best to consult local agronomists or use long‑term observational data.
• Plan several waves – to extend the harvest period, sow seeds at 7‑10‑day intervals (for different varieties or even the same variety). This reduces the risk of losing the entire crop due to one adverse event (Swiader & Ware, 1992).
• Remember hardening off – for early spring transplanting, be sure to harden off seedlings 7‑10 days before planting to reduce the shock of temperature changes.

Example for temperate climate (Central Russia, Northeastern US)

• Early harvest: sow 25 February – 5 March, transplant 25 April – 5 May (with cover), harvest late June – early July.
• Main (autumn) harvest: sow 25 May – 5 June, transplant 1–10 July, harvest September‑October.
• Permissible late date for direct sowing in the ground: early July (for the earliest hybrids), but only as an experiment.

Summary

Choosing the correct sowing date is an art based on knowledge of the biology of the crop and the climatic conditions of your region. In the next chapter, we will discuss how to prepare seeds for sowing to improve germination and vigour.

Why treat seeds?

Cauliflower seeds have three main "enemies" at the start:

1. Seed‑borne infections – pathogens of bacterial blight (Xanthomonas campestris pv. campestris – black rot, a bacterial disease), alternaria (Alternaria brassicicola) and other fungal diseases can survive on the seed surface and inside them (Swiader & Ware, 1992). Without disinfection, diseases will appear on seedlings and be almost impossible to save.

2. Low germination speed – cauliflower seeds germinate more slowly than white cabbage, especially at lower temperatures. Stimulating treatments accelerate emergence and improve uniformity.

3. Soil‑borne fungi – even in sterile substrate, spores of Pythium and Rhizoctonia can cause damping off and root rots. Seed treatment gives protection in the early stages (Startsеv, 2021).

Steps of seed preparation

What do seed companies do?

For reference: in industrial vegetable growing, pelleting is often used – coating seeds with a nutrient‑protective shell. Pelleted seeds are easier to sow singly, have a round shape and increased size. When buying such seeds, no additional preparation is required – they are sown dry; the shell quickly dissolves in moist soil and provides starter nutrition (Kemble et al., 2022).

Step‑by‑step algorithm for the gardener

1. Inspect the packaging – if seeds are treated (coloured, labelled), sow them dry.

2. If seeds are untreated – carry out hot‑water treatment (50 °C, 20 minutes) for disinfection, then dry.

3. If you wish to accelerate emergence – soak for 12–18 hours in warm water with micronutrients or a stimulant, then dry until free‑flowing.

4. Before sowing – ensure seeds are dry so they do not stick together.

What not to do

• Do not soak seeds longer than 24 hours – they will suffocate from lack of oxygen.
• Do not use hot water on old seeds (older than 3 years) – germination may drop to zero.
• Do not combine different methods unnecessarily – excessive treatments may weaken the seeds.

Proper seed preparation is not magic but sound prevention. It does not guarantee a 100% harvest, but it significantly reduces risks at the most vulnerable stage. In the next chapter, we will discuss which substrate is best for growing strong cauliflower seedlings.

Substrate requirements

Cauliflower has higher demands on the soil environment than white cabbage due to its weaker and more sensitive root system in the early stages (Startsеv, 2021). An ideal substrate should have four key properties:

1. Lightness and looseness (high porosity)

Seedling roots need constant access to oxygen. In dense, compacted soil they suffocate, growth slows, and plants become susceptible to root rots (Pythium, Rhizoctonia) (Swiader & Ware, 1992). The substrate should be air‑permeable, with a pore space (voids) of at least 25–30% of total volume.

2. Water‑holding capacity (ability to retain water)

Despite its looseness, the substrate must retain moisture well without drying out between waterings. This is achieved through organic components – peat, compost, or coir. Optimal moisture for cauliflower seedling development is about 70–80% of full water‑holding capacity (FWHC) (Startsеv, 2021).

3. Neutral or slightly acidic reaction (pH 6.0–6.8)

Cauliflower is very sensitive to acidity. At pH below 5.5, plants suffer from aluminium and manganese toxicity and molybdenum deficiency, which manifests as leaf deformation ("whiptail") and failure to form a head (Rubatzky & Yamaguchi, 1997; UMN Extension, 2022). The optimal range is pH 6.0–6.8, where all micronutrients are available.

4. Moderate nutrient content

Cauliflower seedlings are sensitive to excess salts (especially nitrogen). Over‑fed plants become loose, leggy, and do not transplant well. The substrate should contain a starter set of elements in a balanced, slow‑release form (e.g., from compost or a controlled‑release fertiliser) (Kemble et al., 2022).

Commercial ready‑made mixes

The simplest and safest way for a beginner gardener is to buy a ready‑made substrate specifically formulated for vegetable seedlings. Quality mixes (e.g., based on sphagnum peat with perlite and a complete fertiliser) already have optimal pH and structure.

What to look for when buying:

• Packaging must be intact – damaged bags may harbour pathogens.
• Composition – look for mixes with pH 5.8–6.5 and labelled "for vegetable seedlings".
• Do not use universal flower soil – it is often too dense and has a different nutrient balance.
• Check for perlite or vermiculite – these components loosen the substrate and improve drainage. If absent, add them yourself (about 20% by volume) (UMN Extension, 2022).

Advantages of ready‑made mixes:

• Sterilised against pathogens (pasteurised).
• Balanced pH and nutrition.
• Saves time.

Disadvantage: higher cost than homemade mixes, and it may not always be possible to find one with the right pH.

Homemade substrate preparation

For experienced gardeners who want to control every parameter, there are several tested recipes. All components must be clean, free of weed seeds and pathogens.

Substrate preparation before sowing

1. Sieving. Pass the mixture through a sieve with 5–10 mm holes to remove large lumps and stones. This facilitates uniform sowing and prevents waterlogging in dense spots.

2. Sterilisation. Even quality compost may contain fungal spores. Before use, bake the substrate in the oven at 80–90 °C for 30–40 minutes (for small volumes) or drench with hot (70–80 °C) potassium permanganate solution (pink colour) (Swiader & Ware, 1992). After treatment, let the substrate cool and restore moisture (moisten to a "damp sponge" consistency).

3. pH check. If you have litmus paper or a pH meter, check the acidity of the finished mix. If necessary, adjust by adding dolomite lime (raises pH) or sulphur (lowers). For cauliflower, pH should be in the range 6.0–6.8 (UMN Extension, 2022).

4. Moistening. The day before sowing, moisten the substrate to a moisture level where a handful squeezed in the fist crumbles when lightly pressed. Excess water leads to seed rot, deficiency delays emergence.

Filling containers

Fill trays, pots, or flats with substrate, lightly firming (not compacting!). It is important that the soil level is 1–2 cm below the rim – this facilitates watering and prevents washing out. For tray systems (98‑144 cells) special automatic fillers are used, but manually it is enough to fill cells and lightly press with a finger to avoid voids (Startsеv, 2021).

What if the purchased substrate is of questionable quality?

Even ready‑made mixes can sometimes be too dense or acidic. You can improve them by adding:

• Perlite – 10–15% by volume for looseness.
• Dolomite lime – if the pH on the package is below 5.8.
• A little compost – if the mix looks too "empty" (only peat).

But do not overdo it – excess additives can upset the balance.

Summary

A properly prepared substrate is the foundation on which the entire cultivation technology is built. In the next chapter, we move to the sowing process itself: depth, temperature, and moisture required for uniform emergence.

Sowing depth

Cauliflower seeds are small: 2.5–3.5 g per 1000 seeds, diameter about 1.5–2 mm (Rubatzky & Yamaguchi, 1997). Sowing too deep is one of the main mistakes of beginners. Seeds have a limited nutrient reserve, and if placed deeper than 1.5–2 cm, the sprout may not have enough energy to reach the surface.

Optimal sowing depth: 0.5–1.5 cm (Startsеv, 2021; Swiader & Ware, 1992).

• On light sandy and loamy sands – up to 1.5 cm (deeper to prevent drying out).
• On heavy clay and wet soils – 0.5–1 cm (shallower to avoid rotting).

Important rule: after sowing, seeds must be evenly covered with substrate and lightly firmed (rolled). This ensures close seed‑to‑soil contact necessary for capillary moisture uptake (UMN Extension, 2022). You can use a special board or simply press the soil with your fingers.

Pre‑sowing soil preparation

Before sowing, ensure the substrate is:

• Moistened to a "damp sponge" consistency – if squeezed in your fist, water should not drip, but the ball should hold its shape.
• Firmed but not compacted – the surface should be level, without lumps or voids.
• Warmed to room temperature (at least 18 °C).

For sowing in trays or flats:

1. Fill containers with substrate, lightly firm to eliminate voids.

2. Level the surface and, if necessary, lightly roll with a board or hand.

3. Make furrows 0.5–1.5 cm deep (for flats) or use a dibber to make holes in trays.

Sowing arrangement: density and placement

Unlike white cabbage, which is sometimes sown in a common flat and later pricked out, cauliflower is best sown directly into individual containers (trays, pots, peat pellets). This is because of its sensitivity to root damage during transplanting (Swiader & Ware, 1992).

Optimal options:

In a common flat (if trays are not available):

• Furrows 4–5 cm apart.
• Seeds placed 2–3 cm apart in the row.
• After 2–3 true leaves appear, prick out into individual containers (this is less desirable as it increases stress).

Seeding rate: about 1–1.5 g of seeds per 1000 plants (allowing for 80‑90% germination).

Germination temperature

Temperature is the main factor determining the speed and uniformity of emergence. Cauliflower seeds start germinating at soil temperatures above 4–5 °C, but the optimal range is 18–22 °C (Rubatzky & Yamaguchi, 1997; Startsеv, 2021).

Practical recommendations:

• Use a soil thermometer to monitor temperature at seed depth.
• In cold rooms, use heat mats which raise soil temperature by 5–8 °C.
• After emergence, reduce temperature to 15–18 °C day and 10–12 °C night to prevent stretching.

Moisture and watering after sowing

Moisture is the second most important factor after temperature. Cauliflower seeds require constant substrate moisture but cannot tolerate waterlogging, which leads to rotting (damping off, Pythium spp.) (Swiader & Ware, 1992).

The "golden mean" rule:

• Immediately after sowing – water thoroughly by spraying (mist) or bottom watering (tray) to avoid washing away seeds. Ensure water penetrates to seed depth.
• Until emergence – maintain constant moisture, not allowing the top layer to dry out. If using trays or flats, cover them with plastic film or a transparent lid to create a greenhouse effect and reduce evaporation. However, ventilate daily for at least 10‑15 minutes to prevent mould.
• After emergence – switch to moderate watering, preferably bottom watering, to avoid washing the soil and creating excess moisture at the stem base.

How to check if watering is needed: insert a finger 1–2 cm into the soil. If dry – water; if moist – delay watering for a day or two.

Use of covers

To create a stable microclimate after sowing, it is very useful to use:

• Plastic film or glass – for flats and trays.
• Clear plastic lids – for trays (sold as sets).
• Agrospan (white non‑woven) – placed on top; it allows air and light through but retains heat and moisture.

Important: after the first seedlings appear (usually on day 4‑6), the cover must be removed. If left longer, seedlings will stretch, and moisture at the stem base may provoke damping off. Remove the cover gradually: for 1‑2 hours on the first day, then 3‑4 hours, and after 2‑3 days remove completely (UMN Extension, 2022).

Direct sowing (in open ground)

If you still decide to sow directly (see chapter 2), the technique differs slightly:

• Sow in furrows moistened before sowing.
• Depth – 1–1.5 cm.
• Distance between furrows – 50–70 cm.
• In the row, place seeds 3–5 cm apart; after emergence, thin to 30–50 cm between plants (less for early varieties, more for late) (Kemble et al., 2022).
• Be sure to mulch the sowing with peat or compost 0.5–1 cm thick to retain moisture and protect from overheating.

Step‑by‑step sowing algorithm

1. Prepare the substrate – moisten and fill containers.

2. Make holes (furrows or dibbles) 0.5–1.5 cm deep.

3. Place seeds – one per cell (trays) or 2–3 cm apart (flats).

4. Cover with substrate, lightly firm the surface.

5. Moisten (mist or bottom watering) to settle substrate around seeds.

6. Cover with a transparent lid or film to retain moisture.

7. Place in a warm spot at 18–22 °C.

8. Ventilate daily and check moisture.

9. Remove cover when first shoots appear (day 4‑6).

10. Move to a cooler, brighter place (15–18 °C) to prevent stretching.

Summary

In the next chapter, we will discuss how to properly care for emerged seedlings: light regime, temperature fluctuations, watering, and ventilation to grow strong, healthy plants.

1. Light – the main growth regulator

Cauliflower is a long‑day plant, and for normal development seedlings need intensive lighting of at least 14‑16 hours per day (Rubatzky & Yamaguchi, 1997). With insufficient light, plants stretch, become pale, internodes lengthen, and the stem becomes thin. Such seedlings, after transplanting, are slow to establish, root poorly, and often fail to form proper heads (Startsеv, 2021).

How to ensure adequate light:

• Natural light. On a south or southeast windowsill in March‑April, there is still little light (especially on cloudy days). Therefore, even on a sunny window, seedlings need supplemental lighting.
• Artificial supplementation. Use grow lights (LED) or fluorescent daylight tubes (cool spectrum). Place lights 15–20 cm above the plant tops and turn on for 12‑16 hours a day. For small areas, one 36‑40 W lamp per 0.5 m² is sufficient (UMN Extension, 2022).
• Distance between lamps and plants. As seedlings grow, raise the lamps to maintain 15‑20 cm. If lamps are too low, they may burn leaves; if too high, light will be insufficient.

Signs of light deficiency:

• Plants are pale green or yellowish.
• Internodes are long (>2‑3 cm between nodes).
• Stem is thin, bends easily.
• Leaves are small and point upward.

What to do if stretching occurs: if seedlings have already stretched, you can:

• Add dry substrate up to the cotyledon level (stimulates additional root formation).
• Lower air temperature to 12‑14 °C and increase daylight to 16 hours.
• However, severely overgrown seedlings are better discarded – they will not give a good harvest.

2. Temperature – controlling growth rate

Temperature after emergence should be lower than during germination. This is a key principle for growing sturdy seedlings. High temperature combined with insufficient light is the main cause of stretching.

Recommended temperature regime:

Why it works: at low temperatures, stem growth slows (gibberellin synthesis is inhibited), but photosynthesis and dry matter accumulation continue. As a result, plants become stocky, with short internodes and a powerful root system. This is critical for cauliflower, because overgrown seedlings with long stems often break in the wind and establish poorly after transplanting (Swiader & Ware, 1992).

Practical tip: if you cannot lower the temperature in the room, compensate by increasing light and improving ventilation. The ideal is to move seedlings to a glazed balcony or cold frame where night temperatures naturally drop.

3. Watering – balancing moisture and overwatering

Watering cauliflower seedlings requires special attention. The root system of young plants is delicate, and excess moisture quickly leads to damping off (Rhizoctonia solani, Pythium spp.) (Startsеv, 2021). On the other hand, lack of water causes growth arrest and premature tissue ageing.

Watering rules:

• Frequency. Water only when the top 1‑2 cm of substrate has dried. In warm, sunny conditions this may be daily; on cloudy days – every 2‑3 days.
• Method. The best method is bottom watering (into the tray). Water rises by capillary action, moistening the root ball from below, while the surface stays dry, inhibiting fungal diseases. If watering from above, do so gently with a fine stream (preferably a spray) avoiding water on the stem base (Swiader & Ware, 1992).
• Water temperature. Use only settled water at room temperature (18–20 °C). Cold water shocks roots and slows growth.
• Amount. Soil should be thoroughly moistened but not waterlogged. Remove excess water from the tray 20‑30 minutes after watering.

Signs of improper watering:

• Overwatering: wilting leaves with wet soil, darkening of the stem base, mould on the surface.
• Underwatering: loss of leaf turgor (soft, drooping leaves), drying of leaf tips.

Important: after watering, always ventilate the room to reduce air humidity. High humidity (above 85%) promotes fungal diseases (UMN Extension, 2022).

4. Ventilation – fresh air for seedling health

Stagnant, humid air is the main enemy of seedlings. In poorly ventilated spaces, fungal diseases develop quickly, and plants become loose and weak.

How to organise ventilation:

• Open windows or vents daily for 15‑30 minutes (in warm weather), avoiding drafts that can break plants.
• Use a fan to circulate air (at low speed, not blowing directly on plants). This mimics wind and promotes stem thickening (hardening).
• In greenhouses or cold frames, ventilate on sunny days to keep temperature below 22‑25 °C.

Signs of insufficient ventilation:

• Grey mould on the substrate surface.
• Plants are pale with thin stems.
• Damping off (blackening and constriction at the stem base).

5. Fertilisation – when and what to feed?

Cauliflower seedlings are sensitive to excess fertiliser. Over‑fed plants become loose, "fatty", with large but brittle leaves. They transplant poorly and are delayed in growth after planting.

General rule: first feeding is given no earlier than when the second true leaf appears. Second feeding 7‑10 days after the first.

Recommended fertilisers:

• Complete water‑soluble fertiliser with NPK about 20‑20‑20 (or 15‑15‑15) at half the concentration recommended for houseplants (e.g., 5‑10 g per 10 L water if label says 20 g per 10 L) (Startsеv, 2021).
• Pay attention to micronutrients. Cauliflower especially needs boron (B) and molybdenum (Mo) in early stages. Deficiency can show as leaf deformity and stopping of the growing point (Rubatzky & Yamaguchi, 1997). Many specialised seedling fertilisers already contain these elements.
• Nitrogen – in moderate amounts. Excess nitrogen causes stretching and reduces disease resistance.

How to apply:

• Foliar feeding (spray on leaves) with a weak solution (0.5%) on a cloudy day or in the evening is best. This delivers elements faster and reduces the risk of root salt burn.
• For root application – water the solution strictly on moist soil, avoiding contact with stems and leaves.

Signs of excess fertiliser:

• Dark green, overly large leaves.
• Brittleness, fragility of the stem.
• Slowed growth after transplanting.

6. Pricking – necessary or not?

Cauliflower is a crop that does not like pricking very much, as root damage slows growth and may trigger premature formation of small heads (buttoning) (Swiader & Ware, 1992). However, if sown in a common flat, pricking is unavoidable.

Optimal approach: sow initially in individual containers (trays, pots, peat pellets) to avoid pricking. If pricking is necessary:

• Do it at the 2‑3 true‑leaf stage (not later!).
• Use a small spatula or stick to gently lift the plant with a soil ball.
• Transplant into a larger container (at least 8×8 cm), burying to the cotyledons (stimulates additional root formation).
• After pricking, shade seedlings for 2‑3 days and maintain temperature 2‑3 °C higher than usual to speed establishment.

7. Prevention of damping off and other fungal diseases

Prevention is always better than cure. For cauliflower, the main measures are:

• Sterile substrate (see chapter 5).
• Dry soil surface – do not overwater.
• Regular ventilation – reduce air humidity.
• Thinning – if sowing was dense, remove weak plants so the rest do not shade each other.
• Biological products (Trichoderma, Bacillus) – can be added to the substrate at sowing or watered after emergence to suppress pathogens (UMN Extension, 2022).

Summary: daily care checklist

Every morning check:

1. Lighting – are lamps on? Are windows clean? Do plants shade each other?

2. Temperature – does daytime exceed 20 °C? Does night drop below 8 °C?

3. Substrate moisture – feel the top layer and the weight of the pot.

4. Ventilation – is the window open (if needed)? Is air stagnant?

5. Plants – any signs of disease, damage, colour change?

Regular but not excessive care is the key to healthy, stocky seedlings that will quickly start growing after transplanting and reward you with dense, snow‑white heads. In the next chapter, we will discuss why overgrowing seedlings is so dangerous for cauliflower and how to avoid it.

Why is overgrowing dangerous for cauliflower?

1. Direct link to "buttoning" (small heads)

Cauliflower has a critical sensitivity period to stress at the 4‑6 true‑leaf stage. At this time, generative organs are initiated (curd initiation). If the plant experiences stress during this period (including delayed planting, drying, overheating, or root damage), it "decides" to complete its life cycle as quickly as possible and forms a microscopic head – a "button" that will never grow to marketable size (Rubatzky & Yamaguchi, 1997).

Overgrown seedlings are plants that have already passed the optimal transplanting stage. Their roots have filled the entire root ball, stem growth has slowed, but internal ageing processes have begun. When transplanted, such plants experience severe shock, and in response to stress they initiate a head prematurely – before they have accumulated sufficient vegetative mass. The result is a head the size of a walnut instead of a dense curd 15‑20 cm in diameter (Swiader & Ware, 1992).

2. Poor establishment and long adaptation

Overgrown seedlings have a root system already formed in a limited volume and often begins to coil ("root circling"). After transplanting, such roots do not spread well into the new space, the plant takes a long time to start growing, and at the slightest drought or heat it wilts. This delays the head‑formation phase to later dates when weather may no longer be optimal (UMN Extension, 2022).

3. Reduced resistance to diseases and pests

Overgrown seedlings grown in tight containers often have weakened immunity. Their leaves are more tender, and the waxy bloom (natural protection) is less developed. Such plants are more susceptible to alternaria and more attractive to aphids and caterpillars after transplanting (Kemble et al., 2022).

Causes of overgrowing

Overgrowing is always a consequence of mismatch between plant growth rate and transplant timing. The main factors that accelerate growth and lead to overgrowing:

Signs of overgrown seedlings

To spot the problem in time, inspect plants regularly. Typical signs:

• Stem – height over 15‑20 cm (some varieties may be taller, but generally optimal height is 12‑15 cm). Stem thin, bends easily.
• Internodes – distance between nodes more than 2‑3 cm (should be 1‑1.5 cm).
• Leaves – more than 6‑7 true leaves (4‑5 is enough for transplanting). Lower leaves may start yellowing.
• Roots – if you pull the plant out, roots densely wrap the whole root ball, with twisted roots at the bottom.
• Colour – pale green or yellowish (sign of nutrient deficiency or ageing).

Important: for cauliflower, seedling age is critical. Even if the plant looks good externally, if age exceeds 45‑50 days from emergence, it is already overgrown. Optimal age for transplanting is 35‑40 days (early varieties) and 40‑45 days (medium and late) (Startsеv, 2021).

Methods to prevent overgrowing

The best way to combat overgrowing is to calculate sowing dates correctly (see chapter 3). But even with precise calculation, weather anomalies may delay transplanting. Therefore, it is important to use agronomic techniques that slow seedling growth without compromising quality.

1. Temperature control: use a "cold start"

The most effective way to slow growth is to lower temperature. For cauliflower, the optimal day/night temperature ratio is:

• Day – 15‑18 °C (with sufficient light).
• Night – 8‑12 °C.

Under these conditions, stem growth slows, but photosynthesis continues, and the plant accumulates dry matter, becoming stocky. If you see seedlings growing too fast, lower night temperature to 6‑8 °C (but not below, to avoid cold shock). This is safe for cauliflower if plants are hardened (UMN Extension, 2022; Swiader & Ware, 1992).

2. Limited watering

Moderate watering is a powerful growth regulator. Overwatering accelerates vegetation. Water only after the topsoil has lightly dried. This not only slows growth but also stimulates root development, as roots branch more actively in search of moisture.

Important: do not let severe drying occur – that stress can also trigger buttoning.

3. Light regime

With insufficient light, plants stretch. Provide 14‑16 hours of intensive light per day (see chapter 7). The distance to lamps should be no more than 20 cm. If you notice stretching, increase daylight to 16 hours and (if possible) lower temperature.

4. Balanced nutrition (no excess nitrogen)

For cauliflower seedlings, use fertilisers with a higher phosphorus and potassium ratio to nitrogen, especially at later stages. For example, formula 15‑30‑15 or 10‑20‑20. Nitrogen stimulates leaf and stem growth, while phosphorus strengthens the root system and prepares the plant for transplanting. The second feeding (if needed) should have reduced nitrogen.

5. Use of small cells (trays)

In trays with small cell volume (20‑30 cm³), the root system quickly fills the space and then growth naturally slows. This allows you to gain 5‑7 days without overgrowing. For cauliflower, trays of 128‑144 cells are optimal (Startsеv, 2021). If you use larger pots, plants may overgrow earlier.

6. Hardening from early stages

Hardening is not only preparation for transplanting but also a way to slow growth. Take seedlings outdoors (in a sheltered place) when temperatures are above 8 °C, starting from the 2‑3 true‑leaf stage. Start with 1‑2 hours a day and gradually increase to a full day. This reduces growth rate and strengthens tissues.

7. Mechanical techniques (for experienced)

In commercial vegetable growing, light shaking or running a hand over the plant tops is sometimes used – this causes micro‑damage that stimulates stem thickening. For home conditions, this is not necessary, but if seedlings start stretching, you can gently brush the tops with your hand once or twice a day (the "wind" effect).

Pinching is not recommended for cauliflower – removing the growing point may lead to many small side shoots instead of one large head (Rubatzky & Yamaguchi, 1997).

What to do if seedlings have already overgrown?

If transplanting is delayed and seedlings have already overgrown, you can take the following steps:

1. Pot up into a slightly larger container (but no more than 1‑2 cm larger than the previous). This gives roots new space and temporarily stops ageing. Do not disturb the root ball.

2. Strong temperature reduction – if possible, move seedlings to a cooler place (8‑10 °C day, 5‑6 °C night) for 5‑7 days. This halts growth and buys time for transplanting.

3. Limit watering and stop fertilising until transplanting.

4. At transplanting, bury the stem up to the cotyledons, removing lower leaves. This stimulates additional root formation and partially compensates for stretching.

However, remember: even these measures do not guarantee that overgrown seedlings will produce a full head. If seedlings are severely overgrown (height >20 cm, internodes >3 cm, age >50 days), it is better to discard them and either buy new ones or resow (if season allows). Attempting to save such seedlings often ends in disappointment (Swiader & Ware, 1992).

Summary: how to avoid overgrowing – checklist

• [ ] Calculate sowing date precisely (chapter 3) so transplanting occurs at 35‑45 days old.
• [ ] Ensure night temperature of 8‑12 °C from the first days after emergence.
• [ ] Provide 14‑16 hours of supplemental lighting per day.
• [ ] Water moderately, allowing the soil to dry slightly between waterings.
• [ ] Do not overfeed with nitrogen – use balanced fertilisers with more phosphorus and potassium.
• [ ] Choose trays with small cells (20‑30 cm³).
• [ ] Start hardening early (from 2‑3 true leaves).
• [ ] Inspect seedlings daily and adjust conditions at the first signs of overgrowing.

Overgrowing is a management error, but it can be avoided if you monitor plants closely and adjust temperature, light, and watering in time. Remember: for cauliflower, compact, stocky seedlings with 4‑5 leaves are the key to large, dense heads.

In the next chapter, we will cover the final stage of preparing seedlings for transplanting – hardening.

Why harden seedlings?

In protected cultivation (greenhouse, cold frame, windowsill), plants live in "hothouse" conditions: high air humidity, no wind, stable temperatures, and soft light passing through glass or film (which blocks some UV). When suddenly moved to open ground, plants experience severe stress:

• Sunburn – tender leaves, unaccustomed to direct sunlight, get burned, showing white or brown spots. Damaged leaves lose photosynthetic capacity, delaying growth (UMN Extension, 2022).
• Wind load – stems not strengthened by wind break or lodge easily.
• Temperature fluctuations – night frosts even down to -2 °C can damage unhardened plants.
• Transpiration shock – a sharp drop in air humidity leads to intense water loss through leaves, and the root system cannot keep up. The plant wilts and may die (Startsеv, 2021).

Hardening triggers physiological adaptation mechanisms:

• The cuticle (waxy layer on leaves) thickens, reducing evaporation.
• Sugar and other osmotically active substances increase in cell sap, raising frost resistance.
• The stem becomes stronger and more elastic.
• The root system activates and grows faster after transplanting (Rubatzky & Yamaguchi, 1997).

When to start hardening?

Hardening begins 7‑10 days before the intended transplanting date (Startsеv, 2021; UMN Extension, 2022). By this time, seedlings should have 4‑5 true leaves, be stocky, with a well‑developed root system (roots should fill the root ball but not be overgrown).

Important: do not start hardening if:

• Seedlings are weak, diseased, or damaged.
• Outside temperature is below 5 °C (for cauliflower, this is risky, though it is cold‑hardy).
• Strong wind (over 10‑12 m/s) – it may mechanically damage plants.

Hardening methods

Several methods can be combined depending on your conditions.

What not to do during hardening

1. Do not take seedlings outside without preparation. A sudden switch from greenhouse conditions to open sun and wind will cause burns, wilting, and death even in one day.

2. Do not allow frost below -2 °C. Cauliflower is cold‑hardy, but unhardened plants may suffer at -1 °C. Hardened plants can tolerate short frosts down to -3…-4 °C, but it is risky (UMN Extension, 2022). If frost is forecast, bring seedlings back indoors or cover with non‑woven fabric.

3. Do not leave seedlings in midday sun in the first days. Peak sunlight (11 am to 3 pm) is dangerous for unadapted plants. In the first 3‑4 days of hardening, shade them or take them out only in the morning and evening.

4. Do not harden overgrown or weakened seedlings. They may not withstand the stress. It is better to transplant them without hardening but provide cover initially.

5. Do not stop watering completely. Restricting water means moderate drying, not a full drought. Plants must maintain turgor.

How to tell seedlings are ready for transplanting?

Ready seedlings after hardening have the following characteristics:

• Appearance – stocky, short internodes, stem firm, does not break when lightly pressed.
• Leaves – 4‑5 true leaves, dark green, with waxy bloom (some varieties), no burns or yellowing.
• Roots – well developed, fill the root ball (when removed, the ball holds together).
• Ability to withstand sun and wind – plants do not wilt after 2‑3 hours outdoors, leaves show no burns.
• Age – 35‑45 days from emergence.

Additional test: if you leave seedlings overnight at 5‑6 °C and they look healthy in the morning, without wilting or colour change – they are ready.

Summary: hardening checklist

• [ ] Start 7‑10 days before transplanting.
• [ ] Begin with 1‑2 hours outdoors in shade, gradually increase to full day.
• [ ] Avoid abrupt transition to direct sun and strong wind.
• [ ] Keep night temperature above 5‑6 °C.
• [ ] Moderately restrict watering.
• [ ] Stop fertilising.
• [ ] Inspect plants daily for stress (burns, wilting).
• [ ] Leave seedlings outdoors overnight 2‑3 days before transplanting (if weather permits).

Proper hardening is not just preparation for transplanting but a crucial stage that determines how quickly plants will establish and begin to form a crop. In the final chapter, we will summarise and discuss how to recognise that seedlings are fully ready for transplanting into open ground.

1. Physiological signs of readiness

Seedlings are considered ready when they simultaneously meet several parameters:

Important: these parameters are approximate. They may vary slightly among varieties. Always refer to the seed packet recommendations and local agronomic dates.

2. External conditions for transplanting

Even ideal seedlings will die if planted in unsuitable weather. For cauliflower, two factors are critical: soil temperature and the forecast for the next 7‑10 days.

Soil temperature:

• Minimum soil temperature at 10 cm depth for transplanting – 8‑10 °C (Swiader & Ware, 1992).
• Optimal – 12‑15 °C. At this temperature, roots start growing actively, and the plant adapts quickly.
• If soil is colder than 8 °C, the root system does not work, and seedlings "sit still", which may provoke stress and buttoning.

How to check soil temperature:

• Use a soil thermometer, inserting it to 10 cm depth in the morning.
• If no thermometer, use folk signs: birch leaves unfolded – soil warmed to 10 °C; bird cherry in bloom – you can plant cold‑hardy crops (including cauliflower). But these are only rough guides.

Weather forecast:

• Ensure no frost below -2 °C is expected in the next 7‑10 days. Hardened cauliflower seedlings can tolerate short frosts down to -3…-4 °C, but it is risky (UMN Extension, 2022).
• Optimal air temperature for adaptation after transplanting – daytime 15‑20 °C, night not below 8 °C.
• Avoid transplanting during strong winds (>10‑12 m/s) and in dry weather without irrigation capability.

Transplanting dates for major climatic zones (approximate):

Always adjust dates according to current weather, not the calendar!

3. How to transplant properly

Even perfectly prepared seedlings can suffer if transplanting is done carelessly. Follow these simple rules:

1. Time of day. Transplant in the evening (after 5‑6 pm) or on a cloudy day. This gives plants time to adapt before direct sun exposure (Startsеv, 2021).

2. Soil preparation. Beds should be dug, fertilised (see chapter 3 on nutrition needs), levelled, and watered a day before transplanting.

3. Spacing:

• For early varieties: 45‑50 cm between plants, 50‑60 cm between rows.
• For mid‑late varieties: 50‑60 cm between plants, 60‑70 cm between rows.
• Do not overcrowd! Denser planting leads to small heads (Kemble et al., 2022).

4. Planting depth. Bury plants to the cotyledon leaves (the first rounded leaves). This stimulates additional root formation and increases stability. Do not bury above – the growing point must not be covered.

5. Planting technique:

• Carefully remove the plant from the pot/tray, trying not to disturb the root ball. Best is the transplanting method (without breaking the ball).
• Place in the hole, fill with soil, lightly firm around the stem.
• Immediately after planting, water abundantly – at least 0.5‑1 L per plant. This ensures close root‑to‑soil contact (UMN Extension, 2022).
• Mulch the planting with peat, compost, or dry grass 2‑3 cm thick. This retains moisture, prevents crusting, and protects roots from overheating.

6. Protection after transplanting.

• For the first 3‑5 days, shade plants (e.g., with lutrasil, agrospan, old newspapers on hoops) during midday if the weather is hot.
• Use row covers at night if frost is expected.
• Water regularly for the first 2 weeks while plants establish (soil should not dry out).

4. What to expect after transplanting: timeline and signs of adaptation

• 1‑2 days – plants may wilt slightly, even with abundant watering (this is normal until roots start working in the new volume).
• 3‑5 days – new leaves appear (a sign of rooting).
• 7‑10 days – plant fully adapts and begins actively growing the leaf rosette.

If after 10‑14 days plants still look depressed, yellow, or stop growing, check:

• Soil moisture (possibly overwatering or, conversely, drying out).
• Presence of pests on roots (cabbage root fly) or leaves (flea beetles, caterpillars).
• Soil pH (should be 6.0‑6.8).

5. Final checklist for successful transplanting

Before transplanting, check:

• [ ] Seedlings have 4‑5 true leaves, age 35‑45 days.
• [ ] Hardening completed (seedlings can spend full days and nights outdoors at 5‑6 °C).
• [ ] Soil warmed to 10‑12 °C at 10 cm depth.
• [ ] Weather forecast favourable for the next 7‑10 days (no frost, strong winds).
• [ ] Beds prepared (dug, levelled, fertilised).
• [ ] Spacing followed (not overcrowded).
• [ ] After transplanting, watering and, if necessary, shading/cover are provided.

Conclusion

Growing cauliflower seedlings is a process that requires attention to detail and an understanding of the biological needs of this sensitive crop. From the correct choice of sowing dates to proper transplanting – each stage affects the final result. But it is precisely careful preparation that allows you to obtain what cauliflower is valued for: dense, snow‑white (or coloured) heads with a delicate texture and rich flavour.

Remember the main rule: cauliflower does not tolerate haste or stress. Provide it with stable conditions at each stage – and it will reward you with a bountiful, high‑quality harvest.

Summary table of seedling growing stages

Now you have a complete practical guide. Good luck with your growing!