Preparing the soil

Sunlight: The Basis of Life

The plum is an exceptionally light-loving crop. For proper growth, development, and the formation of sweet fruits, the tree needs at least 6-8 hours of direct sunlight per day (Martin, 2019; Cornell Guide, 2003). This is because the process of photosynthesis, through which the plant produces nutrients, directly depends on the intensity and duration of light (Martin, 2019).

Why this is so important for plums:

• Yield and Fruit Quality: With insufficient light, shoots become elongated and thin, and leaves become pale. The number and size of fruits decrease significantly, and they lose sugar content and color intensity.
• Tree Health: Well-lit crowns are better ventilated, which reduces the risk of fungal diseases. The inner parts of the crown, with good lighting, produce more fruit buds, ensuring next year's harvest.

Tip: Choose the most open and sunny spot in the garden for your plum. Avoid areas shaded by the house, tall buildings, or the crowns of other trees. Sunlight should fall on the tree for most of the day.

Terrain: Finding the Ideal Slope

Terrain plays an equally important role as lighting. It determines how cold air and moisture are distributed on your plot.

• Southern, South-Western, and Western Slopes: This is the best choice for plums, especially in regions with cold climates (Agustí, 2010). Such slopes warm up better in the sun; snow melts earlier and the soil warms up faster in spring. This promotes an early start to the growing season and more uniform flowering. In southern, hot regions, on the other hand, preference is given to more humid northern and north-western slopes to protect trees from overheating and desiccation (Kurennoi, 1985).
• Flat Areas: Also quite suitable for cultivation. The main thing is to ensure that cold air does not stagnate there.
• Lowlands, Closed Basins, and Foot of Slopes: These are the most unsuitable places. Cold air, being heavier than warm air, flows down and gets trapped in such "frost pockets," especially on calm nights (Agustí, 2010). This significantly increases the risk of flower damage from spring frosts. Additionally, water often accumulates in lowlands, leading to waterlogged soil and root rot.

Protection from Cold Winds: A Barrier for Health

Plums do not like strong, desiccating winds, especially cold ones (Agustí, 2010). Wind can cause the following harm:

• In Winter: Strong frosty winds dry out the wood and cause "wind desiccation" of branches and bark, reducing winter hardiness.
• In Spring: Cold winds hinder the work of pollinating insects, knock off flowers, and reduce the fruit set percentage.
• In Summer: Hot, dry winds can cause water stress in the tree, leading to small fruit and even fruit drop.

What to do: If your plot is open to all winds, you need to create protection. The ideal solution would be to plant garden protection strips or windbreaks (Kurennoi, 1985; Potapov, 2000).

• Types of Protection: Effective are special garden edges made of fast-growing, tall trees (e.g., birch, maple, poplar) and shrubs, planted on the windward side of the garden. They should be openwork or permeable to avoid creating excessive air turbulence (Potapov, 2000).
• Effect: A properly created shelter reduces wind speed by 30-50% at a distance 12-15 times the height of the trees in the strip (Potapov, 2000). As an alternative, you can use solid fences or walls of outbuildings, but their effectiveness in reducing wind speed is lower.

Risk of Spring Frosts: A Dangerous Period

Plum flowers are among the most sensitive to spring frosts. Temperatures below -2...-3 °C during the flowering period can destroy most of the crop (Kurennoi, 1985).

How to reduce the risk:

1. Choose the Right Site: As mentioned, avoid lowlands and depressions.

2. Select the Right Varieties: In regions with frequent return frosts, give preference to late-flowering varieties. They bloom 5-7 days later and often avoid the most severe frosts (Potapov, 2000).

3. Protection Methods: In small gardens, when frost is threatened, you can use smoke (protection from radiation frosts) or fine sprinkling, which, due to the heat released when water freezes, raises the air temperature in the surface layer (Potapov, 2000).

Groundwater Level: Dry Feet are the Key to Health

The root system of the plum is well developed, but it is extremely sensitive to stagnant water and lack of oxygen in the soil. This is one of the most important requirements.

• Critical Level: The groundwater level should be no closer than 1.5-2 meters from the soil surface (Potapov, 2000; Kurennoi, 1985). When water levels are higher, the roots experience oxygen starvation (anaerobiosis), begin to rot, and the tree, especially on heavy soils, soon dies.
• The Problem of Overwatering: Stagnant water is especially dangerous during the growing season. Plum sensitivity to excessive moisture is very high.
• Solution: If the groundwater on your plot is close, there are two options:
• Planting on Artificial Mounds (Beds): Create a mound 50-70 cm high and about 2 meters in diameter, on which you will plant the sapling.
• Drainage: Organize a system of drainage ditches to remove excess water, but this is a more labor-intensive and expensive process.
• Plum Rootstock: Choose saplings grafted onto clonal rootstocks that are more resistant to overwatering (Gull, 2023).

Soil Texture (Mechanical Composition)

This is one of the key characteristics determining how comfortable your plum's roots will feel. Soil texture depends on particle size (sand, silt, clay).

• Ideal Option: For plums, loamy soils are considered best. They contain a balanced amount of particles of different sizes (Martin, 2019; Westwood, 1993). They have good structure, providing an optimal balance of moisture and air.
• Loams retain moisture and nutrients well, but at the same time are not prone to waterlogging, as they have satisfactory water permeability.
• Heavy clay soils, on the other hand, create many problems. They warm up slowly, compact quickly, and most importantly, they have very little air (poor aeration), which is dangerous for the roots (Agustí, 2010). Water stagnates in clay, which, with high groundwater, almost guarantees the tree's death from root rot.
• Light sandy soils, conversely, are too permeable to water and do not retain it. They dry out quickly and are poor in nutrients, as they are easily leached. A plum on sand will suffer from lack of moisture and starvation (Kurennoi, 1985).

How to Determine Soil Texture on Your Plot?

There is a simple field method, the so-called "ribbon test" or "feel method" (Martin, 2019). Take a handful of moist soil (not wet, but moist enough so it doesn't crumble to dust, but also doesn't stick to your hands like plasticine). Squeeze it in your fist and try to roll it between your palms into a "ribbon" or "sausage" about 5-10 cm long. Then try to bend it into a ring.

• Sandy Soil: A ribbon does not form; the soil crumbles in your hand.
• Loamy Sand: Forms a weak ribbon that easily breaks.
• Loam: Forms a strong ribbon, but when bent into a ring, it cracks and breaks.
• Clay: Forms a smooth, plastic ribbon that easily bends into a ring without cracking.

Soil Structure

Structure is the ability of soil particles to combine into lumps and aggregates. This is what makes fertile soil "airy" and "crumbly" (Agustí, 2010; Martin, 2019). Good structure means that the soil has many pores of different sizes.

• Importance: These pores play a crucial role. Large pores are filled with air, necessary for root respiration and the activity of beneficial soil microorganisms. Small pores retain moisture, which the tree needs during dry periods.
• Ideal Plum Soil has a crumbly-granular structure. Take a handful of earth – it should crumble into separate lumps, rather than be a uniform dusty mass.

Drainage (Water Permeability)

As we have already established, the plum does not tolerate stagnant water at the roots. Therefore, drainage is one of the most important soil properties (Westwood, 1993). The soil must be permeable to a sufficient depth (at least 60-80 cm, but preferably up to 1-1.5 m) so that excess moisture can drain away freely (Gull, 2023).

How to Check Drainage (Simple Test):

Dig a hole about 30-40 cm deep when the soil is moist but not waterlogged. Fill it with water. If the water drains in 1-2 hours – drainage is excellent. If the water stands for a day or more – the place is not suitable for plums; drainage or planting on a mound is necessary (Martin, 2019).

Aeration

This property is closely related to drainage and structure. Plum roots need constant access to oxygen for respiration (Agustí, 2010). In compacted, "choked," or waterlogged soil, where all pores are filled with water, there is no oxygen. Root asphyxia sets in, and they die. Signs of this include:

• Slow growth, small and pale leaves.
• Fruit drop.
• Gum exudation on the trunk and branches.

Water Holding Capacity

While drainage is important for removing excess water, the soil itself must have sufficient water-holding capacity to supply the tree with moisture during dry periods (Westwood, 1993). This is the soil's ability to retain moisture in its pores.

• How it Works: After rain or watering, water seeps down. Part of the water, the most mobile, goes down by gravity. Another part is retained in capillaries and micropores and becomes available to the roots. Ideal soil retains this moisture reserve, gradually releasing it to the plant, but without becoming a swamp.
• Why this is Important for Plums: In European plums, the roots penetrate quite deep (up to 2-3 m or more), but the bulk of the absorbing roots are located in the upper 50-60 cm layer. Soil with good water-holding capacity ensures that even during dry periods, the roots have access to water, supporting fruit growth and the formation of fruit buds for the next year (Westwood, 1993).

Conclusion: So, the ideal soil for a plum is a deep, well-drained, fertile loam with a crumbly structure. If your soil is far from ideal – don't despair! In the following chapters, we will discuss in detail how you can improve its properties to create the best conditions for your plum.

Optimal pH Level for Plums

The plum, like most fruit crops, prefers soils with a reaction close to neutral. The optimal pH range for it is from 5.5 to 6.5 (Agustí, 2010; Gull, 2023; Cornell Guide, 2003). Some sources allow a wider range – from 5.5 to 7.5, but a slightly acidic or neutral environment (pH 6.0 – 6.5) is best for the absorption of all macro- and microelements (Westwood, 1993).

What Does pH Mean?

pH is a measure of the concentration of hydrogen ions in the soil solution. The pH scale ranges from 0 to 14:

• pH 7.0 – neutral reaction.
• pH below 7.0 – acidic reaction (the lower the value, the higher the acidity).
• pH above 7.0 – alkaline reaction.

A difference of one pH unit means a tenfold change in acidity. For example, pH 5.0 is 10 times more acidic than pH 6.0 (Westwood, 1993).

Why is pH so Important for Plums?

The pH value determines the availability of nutrients to the plant's roots, not just their presence in the soil (Westwood, 1993). Most minerals dissolve and are absorbed well only within a certain pH range. When deviating from the optimal level, many elements become insoluble, "locked" forms, and the tree cannot use them.

• In acidic soil (pH < 5.5):
• Availability of phosphorus, potassium, calcium, and magnesium decreases.
• The solubility of toxic elements, such as aluminum and manganese, increases. Their excess can damage roots and cause growth inhibition (Agustí, 2010; Westwood, 1993).
• The activity of beneficial soil bacteria is disrupted, particularly those responsible for converting nitrogen into a form available to plants (nitrification) (Agustí, 2010).
• In alkaline soil (pH > 7.5):
• The availability of iron, as well as manganese, zinc, boron, and copper, sharply decreases (Agustí, 2010; Westwood, 1993).
• This leads to the development of chlorosis – a disease manifested by yellowing of leaves (especially young upper ones) due to impaired chlorophyll formation.
• Phosphorus, calcium, and potassium also become poorly soluble compounds, becoming inaccessible to the tree.

Determining Soil Acidity

Before making any changes, it is necessary to know exactly the current pH level on your plot. There are several ways to do this:

1. Laboratory Analysis (most accurate method): Send soil samples to a specialized agrochemical laboratory. This method provides the most complete information, including recommendations for fertilizer and amendment application (Martin, 2019). This is the "gold standard," especially if you plan to establish a large orchard.

2. Using a Home pH Meter or Portable Tester: These are devices that provide fairly accurate digital readings. They can be purchased at garden centers.

3. Using Litmus Paper (Indicator Strips): A cheaper but less accurate method. The strip changes color depending on the acidity of the soil extract.

4. A Traditional Method: Put some soil in a glass container and pour vinegar over it. If there is active fizzing and gas release – this is a sign of an alkaline reaction (interaction with carbonates). No reaction may indicate neutral or acidic soil, requiring further testing.

Correcting Soil Reaction

If analysis shows that your soil's pH is not within the optimal range for plums, it needs to be corrected. This process should be started in advance, at least a year before planting, as amendments do not act instantly (Martin, 2019; Kurennoi, 1985).

1. If the soil is too acidic (pH < 5.5), liming is carried out:

• Use limestone (dolomite) flour, slaked lime, or chalk.
• The choice of amendment is important. On light soils, use calcium lime (CaCO₃). On heavy and magnesium-poor soils, it is better to use dolomite flour (CaMg(CO₃)₂), which contains both calcium and magnesium (Westwood, 1993; Cornell Guide, 2003).
• Application rates depend on the initial pH and soil texture. For slightly acidic soils (pH 5.1-5.5) and loams, this is about 3-6 tons/ha; on sandy soils, the rate is significantly lower (Trunov, 2012).
• Rule: Lime should be applied 1-2 years before planting and thoroughly mixed with the soil to a depth of 20-30 cm.
• Important: Do not apply lime simultaneously with large doses of organic fertilizers (manure) and ammonium nitrate, as this will lead to nitrogen losses.

2. If the soil is too alkaline (pH > 7.5), gypsuming or acidification is carried out:

• On alkaline, especially solonetzic soils, gypsum (calcium sulfate) is applied. It binds excess sodium and leaches it to the lower horizons, improving soil structure (Westwood, 1993; Trunov, 2012).
• In less critical cases, to create a slightly acidic reaction in the root zone, you can add high-moor (acidic) peat to the planting hole.
• Important: Changing the pH of alkaline soils towards acidity using sulfur is an expensive and lengthy process. On highly calcareous soils (with high calcium content), this is almost impossible (Agustí, 2010).

Special Attention – Active (Free) Lime

The presence of a carbonate (lime) "layer" in the soil is a serious obstacle for plums. This is not just a high pH, but the active presence of lime, which blocks iron absorption, causing severe chlorosis. The allowable active lime content for plums is no more than 8-10% (Agustí, 2010). On soils with high free lime content, plum cultivation is severely inhibited. In such cases, it is better to choose a different site or use container growing.

Organic Matter: The Basis of Fertility

Organic matter is what remains after the decomposition of plant and animal remains. Its main component is humus – a dark, "earthy" substance responsible for fertility (Westwood, 1993).

Why organic matter is so important for plums:

• Improves Soil Structure: In heavy clay soils, organic particles loosen the dense mass, making it more airy and permeable. In light sandy soils, they bind sand particles into aggregates, helping retain moisture and nutrients (Agustí, 2010; Martin, 2019).
• Increases Water-Holding Capacity: Humus acts like a sponge, capable of retaining a large amount of water, releasing it gradually to the tree.
• Is a Source of Nutrition: As it decomposes, organic matter slowly releases nitrogen, phosphorus, potassium, and micronutrients in a form available to plants (Westwood, 1993).
• Supports Life in the Soil: Organic matter is food for earthworms and beneficial microorganisms that process it into plant-available humus, improving soil structure and suppressing the development of pathogens.

What to Use as Organic Fertilizers:

• Well-Rotted Manure or Compost: This is the best choice. Add it to the soil at a rate of 20 to 40 kg per 1 sq. m (or up to 100 t/ha) for a significant improvement in fertility (Kurennoi, 1985; Trunov, 2012).
• Green Manures: These are plants grown specifically to be incorporated into the soil (green manure). They improve structure, enrich the soil with nitrogen and organic matter. The best green manures for the garden are legumes (vetch, peas, lupine) and cereal-legume mixtures (Agustí, 2010; Potapov, 2000). They are sown in the aisles and plowed in autumn or spring.

Improving Heavy (Clay) Soils

Clay soils are often fertile in terms of their mineral composition, but their poor structure and tendency to waterlogging make them unsuitable for plums (Agustí, 2010).

Your Actions:

1. Organic matter is key! Apply large doses of well-rotted manure or compost (up to 20-30 kg per planting hole). Organic matter is the only effective way to loosen heavy clay.

2. Do not add sand! This is a common mistake. Adding sand to clay without a large amount of organic matter does not improve it, but leads to the formation of "concrete" – an even denser and cemented structure.

3. Improve Drainage: If the site is poorly drained, be sure to make drainage ditches or plant the tree on an artificial mound.

4. Protect the Structure: Try not to work with raw (wet) clay soil – this destroys its already fragile structure. Dig or loosen it when it has dried out a little, but has not yet become as hard as a brick.

Improving Light (Sandy) Soils

Sandy soils have the opposite problem: they are too permeable and poor in nutrients. Moisture and fertilizers quickly leach deep down, without staying in the root zone.

Your Actions:

1. Organic matter is key again! Apply large amounts of well-rotted manure or compost. Organic matter will act like a sponge, retaining moisture and nutrients in the root zone.

2. Use Green Manures: Sowing green manure crops on sands is a great way to accumulate organic matter and prevent the leaching of nutrients (Kurennoi, 1985).

3. Clay Addition: Very poor sandy soils can be improved by adding clay (in the form of loam). This will improve their absorption capacity. However, this is a very labor-intensive process.

4. Split Fertilizer Application: On sandy soils, fertilizers are applied not all at once, but in smaller, split portions, so they don't leach out faster than the tree can use them.

Features of Problematic Soils

There are soils that are extremely difficult or impossible to improve.

• Waterlogged and Peaty Soils: Such areas are unsuitable for plums without radical reclamation (drainage). The high groundwater level and lack of oxygen will certainly kill the tree.
• Highly Saline Soils (Solonetz): Characterized by a high content of sodium salts. This makes the soil structureless, dense, and harmful to most plants, including plums. Correcting such soils is a complex process requiring gypsuming and washing, and is often not cost-effective (Westwood, 1993). In such an area, it is better to avoid planting plums.
• Soils with High Active Lime Content: Even with normal pH, a large amount of free lime blocks iron absorption. The problem is difficult to solve. In this case, the choice falls either on using special rootstocks, or on planting in a container (Agustí, 2010).

Conclusion: Soil improvement is a long-term investment in the health and productivity of your plum tree. Regular application of organic matter (compost, humus, green manures) is a universal and the most reliable way to make even imperfect soil suitable for cultivation.

Clearing the Area: Starting with a Clean Slate

The first step is preparing the site itself. It is best to start this work 1-3 years before planting, so that the soil has time to settle and restore its structure (Martin, 2019).

1. Weed Removal: It is especially important to get rid of perennial rhizomatous and root-sprouting weeds (couch grass, thistle, bindweed, bermuda grass) (Kurennoi, 1985; Trunov, 2012). They will not only compete with the young tree for water and nutrients, but can also serve as a haven for pests.

Control Methods: The best way is deep digging with careful removal of roots. The use of herbicides (e.g., glyphosate-containing preparations) is effective, but they should be used strictly according to the instructions, several weeks before planting (Westwood, 1993).

2. Remove Plant Residues: Remove all remnants of previous crops, branches, stones from the site. This will reduce the risk of disease development and facilitate further soil cultivation.

3. Crop Rotation Considerations: Plums should not be planted in a place where other stone fruits (cherry, apricot, peach) or pome fruits (apple, pear) grew before (Kurennoi, 1985; Potapov, 2000). This is due to the phenomenon of "soil fatigue" – the accumulation in the soil of specific diseases, pests, and toxic substances released by the roots.

Recommendation: The best predecessors are perennial grasses, cereals, row crops, or fallow. Rest for the soil should be at least 2-3 years.

Main (Deep) Soil Cultivation: Preparing a Deep Foundation

This stage is one of the most important. Plum roots can penetrate to a depth of 1.5-2 meters or more, but the bulk of the absorbing roots lie in the layer up to 60-80 cm (Agustí, 2010; Westwood, 1993). To create comfortable conditions for them, it is necessary to carry out deep soil cultivation.

1. Deep Loosening or Plowing: Ideally, before establishing an orchard, deep (subsoil) plowing is carried out to a depth of 40-60 cm (Kurennoi, 1985; Trunov, 2012). This destroys compacted soil layers (plow pan), improves water permeability and aeration, and creates a powerful loose layer for root development.

2. Fertilizer Application: Deep plowing is carried out simultaneously with the application of organic and mineral fertilizers (well-rotted manure, compost, phosphorus-potassium fertilizers), so that they are in the zone of the main future roots and available to the tree in the first years of life (Kurennoi, 1985; Trunov, 2012).

3. What to do on a small plot: If you do not have the opportunity to carry out subsoil plowing, it's not a problem. It is necessary to carefully dig the area to the depth of two spade blades (about 40-50 cm), especially carefully – the area of the future planting hole. The main goal is to loosen the soil to a depth of at least 40-50 cm.

Orchard Layout: Creating Order

If you are planting several plums or establishing an orchard, you need to plan the placement of trees. This will provide them with sufficient nutrition area and light for many years.

1. Distance between Trees: Planting schemes depend on the type of rootstock (tree vigor) and variety.

• For vigorous plums on seed rootstocks, the distance between trees in the row should be 4-5 meters, and between rows – 5-6 meters (Kurennoi, 1985; Trunov, 2012).
• For low-growing and semi-dwarf rootstocks (e.g., St. Julien A, Myrobalan), the distance can be reduced to 3-4 meters in the row and 4-5 meters between rows (Hessayon, 1993; Gull, 2023).

2. Row Orientation: In the middle zone and northern regions, plum rows are best oriented north-south to maximize sunlight use (Potapov, 2000). On slopes, rows are always placed across the slope to prevent erosion and retain moisture (Kurennoi, 1985).

Preparing Planting Holes

The planting hole is best prepared in advance, 2-4 weeks before planting, so that the soil has time to settle.

1. Hole Size: The standard size for a plum planting hole is 60-70 cm deep and 80-100 cm in diameter (Tarasov, 1981; Trunov, 2012). The better the hole is prepared, the better the sapling will take root.

2. Filling the Hole: This is a key point. The hole should not be empty!

• The top fertile layer of soil (thrown separately when digging) is mixed with 1-2 buckets of well-rotted manure or compost, 200-300 g of superphosphate, and 50-100 g of potassium fertilizers (potassium sulfate or kalimagnesia) (Tarasov, 1981; Trunov, 2012). Important: Nitrogen fertilizers are not applied to the planting hole! They can burn young roots.
• At the bottom of the hole: Pour a layer of drainage (broken brick, gravel, expanded clay) 10-15 cm thick if the soil is heavy and there is a risk of water stagnation.
• Filling the hole: Then fill the hole 2/3 full with the prepared fertile mixture, forming a small mound in the center. You will place the sapling on this mound, spreading its roots to the sides.
• Planting Depth: The root collar (the place where the roots transition into the trunk) should be 3-5 cm above the soil level after the earth settles (Tarasov, 1981; Potapov, 2000). Deep planting on heavy soils is one of the main causes of plum death (Agustí, 2010). On dwarf rootstocks, the graft union should be 5-10 cm above the soil level (Potapov, 2000).

3. Staking: A sturdy wooden stake about 1.5 m high is immediately installed in the hole to tie the young tree to it for protection from the wind.