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Greenhouses and covers

Liming and fertilizing greenhouse soil with organic matter and ash

For gardeners

5 min read

GREENHOUSES AND COVERS G

Target pH level and base organic matter

For heat-loving crops grown under cover, soil acidity is of critical importance: they will not grow in acidic podzolic, sod-podzolic soils, and peat soils of the Middle belt with a pH value of 3.5–4.5. The soil solution must be shifted to a pH value of 5.5–6.5, which is close to neutral. Constant measurements are not required — it is enough to apply deoxidizing fertilizer and exclude acidifying ones. There is no risk of over-alkalization: the volume of applied substances is incomparable to the total soil mass.

  • Initial pH of acidic soils — 3.5–4.5
  • Target pH in the greenhouse — 5.5–6.5
  • Compost or humus application rate — from 1 bucket/m²
  • Ash application rate — from 1–2 tbsp to 1 cup/m²
  • Limestone flour application rate — 1 cup/m²

The basis for preparing a greenhouse bed is compost or manure humus. These are complete and interchangeable organic fertilizers. They saturate the soil with nutrients, increase the humus content, and improve the physical structure of the soil, making it loose. The base application rate starts from 1 bucket per 1 m² or less, depending on available supplies. If the volume of organic matter is insufficient for the entire area, it is supplemented with wood ash.

Ash serves as an excellent additive to organic matter, eliminating a possible deficiency of micro- and macronutrients. It contains the entire spectrum of plant nutrients in the form of dry residue, with the exception of nitrogen, which burns off completely. It is preferable to apply ash in the autumn. When applied in the spring, it is thoroughly mixed with the soil layer. The dosage ranges from 1–2 tablespoons to 1 cup per 1 m² — depending on the amount of compost or humus applied.

Complex selection of elements and combination rules

In greenhouses, do not combine ash with mineral nitrogen fertilizers (urea, nitrates). Mineral fertilizers negate the beneficial effect of ash on soil fertility. Only organic matter can enhance ash: compost and humus convert the phosphorus and other elements contained in the ash into a form accessible to plants.

The most balanced nutrition in a small volume of soil (in greenhouses, seedling trays, and pot cultivation) is provided by a combination of three components:

  • compost or manure humus;
  • wood ash;
  • liquid humate with a full composition of micronutrients in chelated form.

Liquid humate is applied in the spring once, diluted according to the instructions for base fertilizer application. In soil rich in organic matter, such an application does not cause over-fertilization — toxic oversaturation occurs not from spring application, but from subsequent frequent top dressing. Ash, in this case, binds with organo-mineral colloids and becomes absolutely safe for the root system.

The applied reserve of substances is fully sufficient for plants to form several clusters of tomatoes or 1–2 fruits of melons and watermelons. Plants use elements sparingly: minerals are first directed to the building of stems and leaves, and then redistributed to the forming seeds. The removed vegetative mass consists mainly of a carbon-calcium skeleton with a small content of magnesium, sulfur, and phosphorus.

In the absence of ash, use limestone flour at a dose of 1 cup per 1 m². It acts as a deoxidizer, loosens the soil, and serves as a source of available calcium and magnesium.

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