The commercial production of vegetables in spring depends upon the quality of the seedlings used.
For many years now seedlings have been produced in hotbeds which are more simple and with cheaper equipment.
In Hungary there are 70 sqm of hotbed seedlings producing area per 1 hectare of vegetable crops grown in the open.
Due to structural peculiarities and because of their labour consuming operations, for their preparation and the manure and peat supply for heating, hotbeds are not suitable for the production of seedlings on a commercial scale.
The economic factors accounting for the necessity of erecting greenhouses for the production of seedlings can be determined by considering some basic conditions.
The regional climatic conditions influence but slightly the quality of the seedlings and the costs for maintaining a suitable microclimate inside the greenhouses.
The quality of production is higher than that of hotbed seedlings, the shipping expenses are lower and the plant protection measures less severe.
Early spring climatic conditions in Hungary offer minimum heat, while in greenhouses it is maintained at an optimum level.
Production costs, given in relative values at the rate of 50 millions kcal/hr per hectare annually for the different sources of energy, calculated according to current prices, are as follows:
|Mazut + coal gas
| coal gas
These calculations are made on the basis of the modern type of greenhouses having a covered area of 2.5 hectares (for the early autumn period) and of heated, polyethylene covered greenhouses with a total of 3 hectares covered area (for the late spring period).
The thermal energy monthly distribution is in accordance with the Dt value.
Heat exigent plants, grown in greenhouses, get 250 to 1000 1x of natural sun light, thus a mean temperature of 15 to 20°C can be maintained inside the greenhouse.
Later on, under the influence of the sun energy lighting reaches 10,000 1x, and the inner temperature can easily be raised in conformity with the higher requirements of a given crop.
The maximum utilization of the thermal energy occurs during the November-March period when light energy is at its minimum.
Last year's mean data show that during that period up to 80 per cent of the thermal energy, with insignificant fluctuations, has been utilized.
Glass coverings can effectively be utilized in case different vegetable crops are grown inside the artificially heated greenhouses.