Distinctive climatic conditions exist overt the vast territory of East Siberia.
The cold period at Yakutsk (with temperatures below 0°C)continues for 220 days.
Mean temperatures during the winter months reach minus 40 to 45°C, sometimes dropping to minus 60–62°C.There is a very short period of daylight during the winter.
The extremely severe climatic conditions during the winter aggravate greenhouse vegetable growing.
Greenhouse heating expenses during the winter months in Yakutsk are three times higher than those in Moscow, amounting to 40–45 per cent of all operational costs.
The spring-summer season is characterized by a long day (July days in Yakutsk are 20 hours long) with predominating good weather and high monthly sums of intensive sun irradatiion (table 1).
The direct sun irradation sum for March and April for Yakutsk and Irkutsk is higher than that for Tashkent which lies considerably more in the south and the sun irradation intensity at noon in Yakutsk is not inferior to that in Tashkent at the same time of the day.
During the spring-summer period of the year the climatic resources of East Siberia suffice for a succesful development of vegetable growing in plastic-covered plant-growing structures.
Investigation carried out in the 1960–1964 period have proved that under the conditions prevailing in Central Yakutia, possibilities exist of producing in plastic-covered cold frames seedlings of high-quality medium early cabbage,tomatoes and cucumbers grown in the open.
It has been estimated that the seedlings cost 2 to 2.5 times less than those produced in manure heated hotbeds (table 2).
During the period when plastics cold frames are free of seedlings, they are used for growing early vegetable crops, mainly cucumbers.
In order to protect tender plants from frosts, the plastic cold frames are covered with water-proff reinforced paper.
The investigations carriedout in the 1965–1968 period have proved the significant agro-economic effectivity of early vegetable growing in the spring plastic-covered greenhouses (table 3).
Highest yield (8.87–10.60 kg/sqm), profitability (4.79–8.35 Roubles/ sqm) and lowest prime cost (1.03–0.87 Roub./kg) are achieved through the use of plastic greenhouses furnished with emergency air heating installations at early cucumber planting dates (10–15 May). In this case, calorifiers or heat-generators, operating on diesel fuel are being used.
The cucumber planting dates can be even earlier, about 15–20 April.
In this case, however, the air heating capacity ought to be increased to 500–600W/sqm.
In case of cold weather, the use of additional plastic covers in the