Technologies for growing vegetable transplants in protected soil
6 min read
Preparation of hotbeds and soil mixtures
Growing seedlings in hotbeds has its own specifics, which are important to consider for obtaining high-quality emergence. In hotbeds, seedlings grow slower than in greenhouses, so sowing dates are shifted 7–10 days earlier. This rule is especially important to observe during the winter months, when natural heat and light are insufficient for a quick start.
- Sowing shift in hotbeds — 7–10 days earlier
- Soil for pot-grown seedlings — 6–7 cm
- Soil for bare-root seedlings — 14–16 cm
- Optimal soil for tomato — 15–17 °С
- Optimal soil for cabbage — 13–14 °С
The thickness of the applied soil in hotbeds with bio-heating depends on the cultivation technology of seedlings. For pot-grown seedlings, a layer 6–7 cm thick is applied, while for bare-root seedlings, the layer is increased to 14–16 cm. To fill hotbeds, agronomists usually use two types of soil mixtures:
- a mixture of humus (1 part) and sod soil (2 parts);
- a mixture of humus, peat, and sod soil in equal parts.
If the hotbed does not have artificial heating and plants are grown on natural soil, soil preparation is carried out using the same technology as in standard greenhouses.
When using biofuel, strictly monitor the gas regime to prevent ammonia poisoning of the seedlings. You can sow seeds and prick out seedlings only after the biofuel has completely heated up and passed a certain stabilization period.
Management of the soil temperature regime
The soil temperature during the seedling growing period directly determines the structure of the future harvest and the profitability of production. Deviation of the temperature from the optimum disrupts the balance between root growth and the aerial part, causing the plants to become leggy and take root poorly. To maintain optimal parameters, combined heating systems are used in greenhouses, or the air temperature is regulated.
| Crop | Soil temperature regime | Effect on seedlings and yield |
|---|---|---|
| Early white cabbage (period from pricking out to hardening) |
Optimal (combined heating): night and morning 10–11 °С, day 14–16 °С, daily average 13–14 °С. Increased: night and morning 15 °С, daily average 16–17 °С. Decreased (only air heating): night and morning 7–8 °С (in certain periods down to 5–6 °С), day 12–14 °С, daily average 11–12 °С. Without soil heating: natural soil warming. |
Balanced seedlings are formed with a strong root system. Growth of the aerial part increases to the detriment of roots. Head mass decreases, early yield drops by 30%. Plant growth is delayed in the greenhouse and in the field. Photosynthetic potential and the intensity of head development decrease. Early yield decreases by 19%, total yield — by 14%, and the profitability level drops by 41%. |
| Cauliflower |
Optimal: 2–3 °С higher than for early white cabbage. Decreased: night and morning 10–11 °С, daily average 13–14 °С. Critically low (only air heating): night and morning 7–8 °С, day 11–12 °С. |
Ensures rapid seedling development and maximum early harvest. Soil heating is mandatory. Early yield decreases by 10%. Early yield decreases by 40%. The plant's absorption and uptake of phosphorus, potassium, and calcium are weakened, and the synthesis of sugar and proteins slows down. |
| Tomato |
Optimal (from emergence to hardening): daily average 15–17 °С. For 50-day bare-root seedlings without pricking out: daily average 15–17 °С (soil and air heating required). For 65-day pot-grown seedlings with pricking out: daily average 15–17 °С (air heating is sufficient). Without soil heating (mass planting dates): daily average 13–15 °С. |
Compared to a temperature 4 °С higher: shoot growth is restrained without loss of root mass, the first floral cluster is set lower, and leaves thicken. Survival rate improves, early yield increases by 29%, profitability — by 35%. Ensures uniform plant development with direct sowing. Compared to combined heating (at 19 °С): shoots grow moderately, the proportion of roots in biomass increases, their aging slows down, and more dry matter is accumulated. The period from sowing to emergence stretches to 12–13 days. For comparison: at 18–20 °С, seedlings appear in 6–8 days, and at 23–25 °С — in 4–5 days (the source erroneously states 45 days). |
When growing tomato seedlings for mass planting dates in unheated plastic greenhouses, consider weather risks. Lower temperature and improved light conditions in such structures harden the seedlings and positively affect their physiology. However, in a cold spring without additional heating, it is difficult to obtain standard seedlings, especially when growing without pricking out. During this period, air heating is necessary to dry the soil, accelerate emergence, and maintain the minimum night temperature.
For cauliflower, soil heating is strictly mandatory. Even a slight cooling in the root zone to 10–11 °С reduces the early harvest by 10%, and if the temperature drops to 7–8 °С, nutrient deficiency leads to a 40% loss of the early harvest.
Plant growth follows a diurnal rhythm and depends directly on fluctuations in the external environment. For proper development of seedlings, the dynamics of temperature are more important than the average daily temperature. Daytime heat activates essential life processes in the tissues, which helps compensate for the coolness of night and morning hours when the temperature drops below the optimum. Therefore, the heating system must flexibly adapt to the needs of a specific crop.
Combining air and soil heating for different crops
The choice of a greenhouse heating scheme depends on the heat requirements of the plants, their planting dates, and the cultivation technology. While for some crops it is sufficient to heat only the air, for others it is critically important to maintain a warm soil environment. Combining air and soil heating allows for producing transplants exactly by the planned date.
| Crop | Technology features and timing | Recommended heating type |
|---|---|---|
| Pepper, eggplant | Growing seedlings without prickling | Soil and air |
| Early white cabbage, cauliflower | — | Soil and air |
| Tomato | Early planting dates, growing without prickling | Soil and air |
| Tomato | Extra-early planting dates, growing with prickling | Air only |
| Tomato | Mass planting dates | Air only |
| White cabbage | Mid-season maturity | Air only |
- Age of ready-to-plant pepper and eggplant transplants — 45–50 days
- Temperature for mid-season cabbage without heating — 13–14 °С
- First sowing date for mid-season cabbage seed — March 20
Growing high-quality pepper transplants and eggplant without prickling while heating only the air is impossible. Due to cold soil, seedling emergence is delayed, and the plants do not have time to develop by the time of transplanting at the optimal dates.
When growing white cabbage transplants of mid-season maturity in unheated greenhouses, the temperature stays at 13–14 °С. However, for the first seed sowing date (March 20), it is recommended to provide emergency air heating — it is necessary for drying and warming up the soil.
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