150 VEGETABLE FORCING 
Amount of water required—An enormous amount of 
water is required to grow good greenhouse crops. As 
previously stated, it enters into the composition of the 
plants, but most of the water which enters the roots 
escapes by transpiration from the leaves. There is also 
rapid evaporation from the soil. Wright, after making 
a survey of this question in nearly 75 commercial green- 
house establishments, estimates that the average daily 
requirement of water during the months of May and June 
is 280 gallons per 1,000 square feet of bed surface in crops, 
or over 12,000 gallons to the acre. Expressed in differ- 
ent terms, 243 gallons of water would be required daily 
per acre during the months of May and June, and under 
certain conditions more than that amount might be 
needed, to meet the requirements of the crops. 
Much more water is required during the late spring 
and early summer months than through the winter. The 
heat rays of the sun are then intense, and with the ven- 
tilators and doors open there is the most rapid escape of 
water from both the plants and the soil. Again, at this 
season of the year the days are longer and there is much 
more sunshine than during the winter months. 
The character of the weather at any particular season 
of the year is also an important factor. It is readily 
understood that less water will be required on cloudy 
days than in bright, sunny weather, and this matter 
should have the most careful consideration of the grower. 
The kind of crop under cultivation is also an important 
factor to be considered. Generally speaking, tomatoes 
and cucumbers require more water than does lettuce. 
Crops which are well advanced or approaching ma- 
turity, necessarily require more water than young plants, 
though there may be diminished evaporation from the 
surface of the beds because they are shaded by the crops. 
Soils which are very open and porous, due to a large 
