CONSTRUCTION OF GREENHOUSES 127 



sash are hinged on the headers, opening at the ridge; 

 while there is, on the other hand, greater danger of cold 

 drafts striking^ the plants, and rain and snow are easily 

 admitted with this form of ventilation. But when nouses 

 are used until midsummer or later, hinging on the header 

 is probably the better plan. Side ventilators are often 

 provided, but many growers regard them as of doubtful 

 utility. They are most useful in warm weather. But 

 whatever the method of ventilation, it is of the greatest 

 importance that the ventilating machinery work easily. 



183. Beds, benches and walks. A few years ago green- 

 house growers thought it essential to provide benches 

 with bottom heat for practically all greenhouse crops, 

 but the opinions held today are different. In many 

 of the largest and most successful houses there are no 

 benches or even beds with board, brick or concrete sides. 

 These mammoth houses often have large doors at the 

 ends so a horse and cart can enter with manure or other 

 supplies. It is also possible to use plow and harrow in 

 the preparation of the soil for planting. While all green- 

 house growers do not approve of horse tillage under 

 glass, some of the most successful growers always use 

 horse implements in preparing ground for the fall crop. 



Benches are convenient in the handling of flats and 

 potted plants, but they are expensive to construct and 

 maintain unless made of concrete. 



Solid beds, with or without sides, provide more uni- 

 form soil conditions than do shallow beds. There is less 

 danger of injury from improper watering and, therefore, 

 the chances of success are increased. Solid beds are espe- 

 cially advantageous when the watering must be intrusted 

 to men of limited experience. 



The walks should be arranged so that all the beds can 

 be cared for conveniently. Beds or benches 5 feet wide 

 and walks or alleys 18 inches in width make a desirable 

 combination, although the relative width of beds in com- 



