Autumn is an important stage for garden owners in preparing fruit trees and berry bushes for the next season. After fruiting ends, plants gradually enter a state of winter dormancy. However, before the cold weather arrives, their root systems can still absorb nutrients. Properly selected fertilizers help provide trees with the necessary elements, support their resistance to adverse conditions, and lay the groundwork for the future harvest.
At the same time, not all fertilizers are suitable for autumn use, and excessive fertilization can do more harm than good. Which products should be chosen for apple, pear, plum, and cherry trees and berry bushes, how should they be applied correctly, and is it possible to manage with organic fertilizers alone? UNN explains.
Why the garden needs fertilizing in autumn
Throughout spring and summer, fruit trees use nutrients for shoot growth, leaf formation, flowering, and fruit development. Some of these elements come from the soil, so their reserves may decrease during intensive fruiting. After the harvest, plants continue accumulating nutrients in their roots, trunks, and branches. They use these reserves when growth resumes in spring, particularly before the root system begins functioning actively.
Experienced gardeners advise beginners that fertilizers do not need to be applied every year. If a tree is healthy, growing normally, and the soil is supplied with nutrients, additional fertilization may be unnecessary.
And the most accurate way to determine whether bushes and plants in the garden need support with fertilizers is through soil analysis.
What nutrients plants need in autumn
For autumn fertilization, fertilizers containing phosphorus and potassium are most often used. These elements play an important role in root-system development and the physiological preparation of perennial plants for the winter period.
Phosphorus is involved in energy metabolism, root development, and other vital processes. Its deficiency can suppress plant growth and negatively affect productivity. Potassium regulates water balance, participates in enzyme activity, and helps plants withstand drought and low temperatures. Magnesium is necessary for photosynthesis because it is part of chlorophyll. Its deficiency may manifest as yellowing of the leaves between the veins and general weakening of the plants.
Nitrogen fertilizers, on the other hand, should be used with caution at the end of the season. Excess available nitrogen can stimulate late growth of young shoots, which will not have time to mature before frost.
It is important to bear in mind that phosphorus and potassium fertilizers do not necessarily have to be applied together. If the soil contains enough of one of these elements, applying more will not provide the expected benefit.
Superphosphate: how to use it correctly in autumn
Superphosphate is one of the most common phosphorus fertilizers. It is used to replenish phosphorus reserves in the soil, particularly under apple, pear, plum, and cherry trees and berry bushes.
There are two main varieties:
- simple superphosphate, which usually contains about
16–20% available phosphorus expressed as phosphorus oxide;
- double superphosphate, in which the phosphorus concentration
is significantly higher and may be about 40–50%.
Therefore, approximately half as much double superphosphate is needed to provide the same amount of phosphorus.
When phosphorus is needed, approximate application rates may be 30–50 g of simple superphosphate or 15–25 g of double superphosphate per square meter of the area beneath the canopy. The exact dosage depends on the results of the soil analysis and the composition of the product. The granules should be distributed evenly throughout the root zone and carefully incorporated into the upper soil layer. Phosphorus is immobile, so surface application without incorporation may be less effective.
Potassium sulfate: how it helps plants prepare for the winter cold
Potassium sulfate, also called sulfate of potash, contains approximately 50% potassium calculated as potassium oxide, as well as sulfur. Its advantage is the absence of chlorine in its composition. Therefore, this fertilizer is suitable for crops sensitive to excess chlorides, including some berry plants. Potassium participates in regulating water exchange and maintaining the normal condition of plant cells. With an adequate supply of this element, plants are better able to withstand adverse conditions.
Potassium sulfate can be applied to fruit trees, currants, gooseberries, raspberries, and grapes.
When a need has been confirmed, the approximate rate for garden crops is 15–30 g per square meter; however, it must be adjusted according to the condition of the soil and the manufacturer's instructions. The fertilizer is applied to moist soil, lightly incorporated if necessary, and watered. At the same time, additional potassium will not increase frost resistance if the plant is already receiving it in sufficient quantities.
Monopotassium phosphate: when fast-acting fertilization is needed
Monopotassium phosphate differs from superphosphate in that it contains both phosphorus and potassium and dissolves well in water. Its composition is usually indicated by the formula 0-52-34. This means that the fertilizer contains no nitrogen but has a high concentration of phosphorus and potassium. It is used for root fertilization with watering or for spraying the leaves. This method makes it possible to deliver nutrients to plants more quickly during the active growing season.
However, there is an important limitation: foliar fertilization is effective only when functional green leaves are present. After leaf fall, spraying with monopotassium phosphate practically loses its purpose. Therefore, this fertilizer is more appropriate to use at the end of summer or the beginning of autumn if there is a confirmed need for nutrients.
The concentration of the solution should be determined according to the instructions for the specific product. Concentrated solutions of monopotassium phosphate should not be mixed with calcium- and magnesium-containing fertilizers without checking their compatibility.
Kalimagnesia: which plants benefit from it most
Kalimagnesia provides plants with three elements at once: potassium, magnesium, and sulfur. It can be especially useful on sandy and sandy-loam soils, where magnesium may be leached more quickly than from heavy soils.
Kalimagnesia is used for fruit trees, grapes, berry bushes, and certain ornamental crops. However, the need for it should be determined based on the soil's potassium and magnesium levels. The approximate rates for some products are 20–30 g per square meter, but the nutrient content of products from different manufacturers may vary.
If the soil contains sufficient magnesium, it is more appropriate to use a conventional potassium fertilizer when there is a potassium deficiency rather than applying both elements unnecessarily.
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Can mineral fertilizers be replaced with organic fertilizers
Not all garden owners want to use mineral products. Organic materials, primarily compost and well-rotted humus, can serve as an alternative or supplement. They improve soil structure, help retain moisture, and gradually release nutrients.
Compost can be spread over the soil surface beneath trees in a layer approximately 2–4 cm thick, leaving free space around the trunk. Such a layer will also serve as mulch.
Another readily available material is wood ash. It contains potassium, calcium, and other mineral elements, but its composition depends on the type of wood. Ash also increases soil alkalinity. Therefore, it is not recommended for regular use without determining the acidity level, especially around blueberries and other plants that require an acidic environment.
Fresh manure should not be applied directly near the roots because of the risk of damaging the plants and supplying excessive amounts of nutrients.
It is important to remember: organic fertilizers cannot always completely replace mineral fertilizers when a specific deficiency needs to be corrected quickly. Excessive application of them can also lead to the accumulation of phosphorus and other elements.
How to properly fertilize different garden crops
The need for fertilizers depends on the plant’s age as well as its species, soil condition, and fruiting intensity.
Apple and pear trees
In soils deficient in phosphorus or potassium, superphosphate and potassium sulfate can be used. For mature trees, fertilizers should be distributed over the area beneath the canopy rather than piled near the trunk.
Cherries, sweet cherries, and plums
These crops also require balanced mineral nutrition. Excess fertilizer cannot compensate for improper care, root damage, or problems with soil acidity.
Currants and gooseberries
Potassium sulfate can be used to replenish potassium reserves. Additional mulching with compost is advisable. Loosening should be done carefully, as some of the roots are located close to the surface.
Raspberries
After fruiting has ended, it is important to remove spent canes in varieties for which this is предусмотрено by the cultivation technology and to keep the soil in proper condition. If necessary, potassium fertilizers can be applied, and the spaces between rows can be mulched with organic materials.
Grapes
Potassium plays an important role in the development of grapevines. Potassium magnesium sulfate may be useful if the soil lacks both elements. At the same time, late nitrogen fertilization is undesirable.
Young saplings
They should not be fertilized according to rates intended for mature trees. If the soil was supplied with nutrients during site preparation, additional application may not be necessary.
When and how to apply autumn fertilizers
The optimal period for most autumn fertilization falls in late August, September, and October. The exact timing depends on the crop, temperature, and soil moisture.
At the beginning of November, some fertilizers can still be applied if the ground is not frozen, but rapid absorption of nutrients should no longer be expected. It is especially important to take the plant’s condition into account. If the leaves have fallen and the soil has cooled, root-system activity decreases significantly. Under such conditions, it is better to focus on mulching and preparing the garden for winter, and schedule corrective fertilization for the appropriate period of the next season.
When applying fertilizers, several rules should be followed:
- distribute fertilizers over the area beneath the tree canopy, avoiding
contact with the trunk;
- carefully incorporate the granules into the upper layer of soil without
damaging the roots;
- follow the dosage and take the concentration of the active
ingredient into account;
- in dry weather, ensure sufficient soil
moisture;
- do not apply fertilizers to frozen ground, before heavy
rain, or in waterlogged areas.
Particular attention should be paid to soil acidity. It affects the availability of nutrients, so sometimes the problem is not a lack of fertilizer but the fact that plants cannot properly absorb it.
The most common mistakes when fertilizing in autumn and how to avoid them
One of the main mistakes gardeners make is believing that a larger amount of fertilizer will necessarily ensure a better harvest. In fact, an excess of minerals can disrupt the nutritional balance and worsen the condition of plants.
An equally common mistake is using a universal dosage for all crops. For example, a mature apple tree and a young currant bush have different nutrient requirements.
It is also undesirable to apply fertilizers without taking weather conditions into account, use high doses of nitrogen before frosts, or mix products whose compatibility is unknown.
Another problem is trying to correct the consequences of diseases, root damage, or a lack of moisture through fertilization. In such cases, the first step is to eliminate the cause of the plant’s deteriorating condition.
Reminder
Earlier, we reported on what every garden-plot owner needs to know.