For many decades vegetable seedlings for planting in the open had been grown in hotbeds.
The use of the polyethylene plastic gave the possibility to have cheap spring hothouses with favourable climate for seedling production.
These last four years the Chair of Vegetable Growing of the Leningrad Agricultural Institute carried out special investigations on the growing of seedlings in spring plastic hothouses.
These investigations yielded good results which have already been applied on specialized vegetable state farms on a large scale.
The studies comprised: 1) types of hothouses as structures for growing seedlings (seven and four link, arched, double pitched, nonstationary tunnel blocks and special block hothouses with two links); 2) heating methods (biological, caloriferic, water heating); 3) dates of sowing and growing of the seedlings; 4) the possibility of growing without pricking out; 5) the container method of growing (in flats); 6) ways of increasing the output of seedlings per square meter; 7) the hardening of seedlings and hothouse ventilation methods.
Experiments were carried out with seedlings of early, medium and late varieties of white cabbage, cauliflower, red cabbage, and Savoy cabbage.
The main conclusions are the following:
- The construction cost of 1 sqm of spring plastic hothouses is 1,5–2 times lower than that of hotbeds.
In such hothouses watering, transport work, disease and insect control measures can be greatly mechanized.
The work on seedling growing in hothouses can be carried out under various weather conditions, the productivity of labour being higher than that in hotbed farming.
- The microclimate in plastic hothouses was much different from that in the hotbeds: the coefficient of light penetration in hothouses was 68–72 % and in hotbeds 38–44 %; light distribution in hothouses was uniform and in hotbeds there was partial overshading in the zone of the south wall; air moisture in hothouses with sufficient impermeability was higher than in hotbeds, but when ventilation was used optimal moisture was attained.
When polyethylene plastic was used, enabling the penetration of 80% of the long wave part of the spectrum, an intensive cooling was found in hothouses not heated; at night time and at critical hours the difference between indoor and outdoor temperatures was only 2–3°C. Such variations of diurnal and night temperatures helped in training the seedling.
In heated hothouses there were negligible if any variations of temperature.
- The best hothouse types with proper microclimate and giving a good complex training are the seedling block hothouse with two links and the