3i8 Diseases of Greenhouse Crops 



Roses {Rosa galUca chinensis). 



Cultural Considerations. As soon as the cut- 

 tings form roots which are about one-half inch in 

 length, they should be potted. At this stage, if 

 left too long in the propagating bench, the wood 

 tissue of the cutting will harden and the subsequent 

 health of the plant will be endangered. A medium 

 water-holding capacity is an indication of a good 

 potting soil for roses. Most greenhouse (fig. 64) 

 varieties prefer a heavy loam. Other varieties such 

 as the Maryland thrive best in a soil which contains 

 a large percentage of sand. Roses are very sensi- 

 tive and readily become injured when given partly 

 decayed organic matter. The case, however, is dif- 

 ferent when well rotted manure is used, for this 

 latter food exerts a wholesome stimulating effect. 

 The development of a good root system largely de- 

 pends on the soil texture and on the plant food which 

 it contains. It is necessary to stir frequently the sur- 

 face soil of rose benches. This not only destroys 

 weeds, but also provides aeration. However, as 

 soon as the surface soil becomes filled with feeding 

 rootlets of the rose plants, the cultivating should be 

 done very superficially or should cease altogether. 

 During active growth, the plants require an abun- 

 dance of ventilation and a comparatively low 

 temperature. 



Diseases of the Rose 



Greenhouse roses are subject to the attacks of 

 several important diseases. 



