Effective methods for maintaining night temperature in a spring greenhouse

Today, advertisements offer all sorts of heating "belts" and "tapes" — new-generation heaters for greenhouses. How necessary are they, and what effect can they provide?

Any greenhouse, for all its perfection, is always ready to lose to the night chill. This is its most vulnerable point. At night, there is no main friend and protector of the greenhouse — the sun, so it is, if not completely powerless, then weak. It can exceed the outside temperature by only a few degrees (3–5 °C).

If the night temperature in summer is 10–15 °C, then inside the greenhouse it will be 15–20 °C, which is quite acceptable for plants (and even then, this is only towards morning, while at midnight after a hot day, the resort-like echoes of the heat still linger in the greenhouse). Therefore, in summer, even on moderately cold nights, everything continues to grow well in greenhouses.

But in the spring or in late summer and autumn, when near-zero temperatures with occasional light frosts are normal for nights in the Central region, our greenhouses hold no more than 5–10 °C by morning. At such temperatures, tomatoes, melons, and watermelons do not grow, only cabbage with onions and other cold-hardy vegetables, which thrive in the form of seedling trays during this early May period in the greenhouse.

Tomatoes and peppers in early May, as they say, "spin their wheels"—they move in fits and starts, i.e., at a certain time of day they grow thanks to the heat accumulated during the day, but at night they freeze in stress at some point. Yes, during the day in the sun in April and May, the temperature easily rises to 30 °C, warming up the interior, the soil, and all sorts of auxiliary concrete aids like paths and tables quite well, but this heat is not enough for the whole night.

Hence the gardeners' desire to mitigate this "spinning of wheels," to add at least a few degrees for the duration of the night.

How to achieve this

Knowing how to "warm up the interior" is enough for confident placement of heat-loving transplants in early and mid-May, and sometimes even in late April. To do this, one does not delay closing the doors until sunset, but closes them closer to the evening while the sun is still quite high to accumulate heat. At this hour, there will be no overheating, but the warming up for the night is the most appropriate.

In greenhouses, besides that, they sometimes place large containers with water, up to a barrel. The water accumulates solar heat during the day and then slowly releases it at night. The container must be covered with a lid so that evaporation does not cool it prematurely. Or, hot water is poured directly into lidded buckets for the night.

Finally, we have inherited a great multitude of stove heating variants from Soviet-era enthusiasts, featuring various ingenious ducts for warm air.

We will not discuss them, as today there are economical electric heaters for sale: heat lamps, special greenhouse heaters, etc. Their use is much simpler than burning wood, and the heating from them is much more uniform. They are turned on at night — and now no, even heavy, frost is able to destroy vulnerable transplants.

Of course, expenses are most justified in the case of a large seedling nursery, when, as an avid gardener, you have in the greenhouse, in addition to tomatoes, everything growing in trays: flower seedlings, strawberries, onions, cabbages, and, of course, the entire nightshade family…

With a facility of 3 greenhouses, it is quite possible to equip only one of them with a heating system so that in March–April you can keep all your transplants there instead of crowding them at home on windowsills.

I would like to say a special word about growing transplants (as part of our general conversation about the significant expansion of a plant grower's creative possibilities with the acquisition of a greenhouse).

Transplants feel much better in a greenhouse throughout their entire growth period than in indoor apartment conditions. And if the opportunity arises to grow them in a greenhouse, it should be taken. They will turn out stronger.

The greenhouse is much brighter, the air is humid, there is more space, and you can use larger pots for the plants. In addition, the transplants of many crops prefer coolness:

• all cabbages;
• onions;
• celery;
• perennial flowers and some annual flowers;
• strawberries from seed;
• potatoes from seed.

These are all frequent victims of dry and warm indoor air. In apartment conditions, they often simply dry out at the root at an early age, whereas in a greenhouse, there are no losses. They all feel so wonderful that they can be left there for the working week, with care provided only on weekends. These cold-resistant crops easily withstand the frosts presented in the table:

Anyone who has already faced the problem of finding free space for the next batch of seed sowing on windowsills will share the excitement of the greenhouse opportunities that have opened up.

We have been talking about using light thermal supply for the greenhouse to relatively slightly extend the growing season in spring. There is, however, a more serious option for greenhouse heating for winter, year-round use, but we will not discuss it here. We are only talking about regular summer use of PC greenhouses.

How to protect a spring greenhouse from night frosts

Early commissioning of a greenhouse in February or March is economically unjustified. During this period, the daylight hours are still too short, and plants critically lack natural lighting. To compensate for the lack of sun, you would have to heat the room around the clock, install powerful supplemental lighting, and spend money on additional insulation of the structure.

The main task of the spring season is to protect plantings from a sharp drop in temperature at night. This is the most vulnerable point of greenhouses, which an agronomist needs to remember throughout the entire growing period. Night frosts combined with wind pose a particular danger to fragile transplants.

Simple and budget-friendly preventive measures help solve the problem of cold air penetration. Every spring, strictly before moving plants into the bright space, it is necessary to carry out routine maintenance of the structure. The main task at this stage is to completely eliminate drafts.

1. Inspect the joints and find gaps between the polycarbonate sheets.
2. Seal large gaps airtight with tape.
3. Check the tightness of doors and vents before planting the transplants.