FORCING AND FORCING STRUCTURES 



55 



under the general management of the different crops. However, 

 some attention can profitably be given here to forcing structures 

 and their management. 



Forcing structures. Forcing structures are of two types tempo- 

 rary and permanent. The hotbed is the simplest forcing structure, 

 but is usually a temporary affair and cannot be looked upon as 

 more than a side issue in market gardening or trucking. It may, 

 however, be advantageously used for lengthening the season, for 



FIG. 12. Commercial cold frames properly arranged for cucumbers 



bringing on a crop in advance of its normal season, or for growing 

 a very short-season crop like lettuce or radishes. 



Cold frames. As the name implies, cold frames are sash-covered 

 frames without heat. The application of heat transforms them at 

 once into hotbeds. While cold frames can hardly be accorded the 

 dignity of forcing structures, yet they play an important part in the 

 protection of plants in autumn and spring, as well as during the win- 

 ter. In some important Southern crop-producing areas cold frames 

 are the chief reliance of the growers. 



Commercial cold frames are constructed, as shown in figure 12, 

 by placing parallel boards with space enough between- to carry 



