172 PLANT GROWTH 



the top foot of soil when preparing permanent areas for lawn 

 or perennials. A ton of ground limestone and a ton of finely 

 ground phosphate rock per acre may be used. Ground bone 

 meal may be used to supply the phosphorus and to add a 

 part of the calcium. Opinion differs regarding the frequency 

 of applying lime, but it is safe to be guided by the change in 

 the pH. Plants thrive in a range of one pH or more, that is, 

 for most garden plants a favorable range goes from 5.6 to 

 above 7 pH. 



In the more specialized technique mineral salts have been 

 used in water solutions for many years for growing plants in 

 experiments like the one explained in this chapter, but 

 recently the method has been modified for use in commercial 

 greenhouse culture, where it is believed that, at least under 

 some circumstances, it is more economical than the use of 

 soil. Flowers and vegetables grown by this method, called 

 "hydroponics," are available now in many markets. Many 

 people are using this method of growing plants as a hobby, 

 but to be successful it requires a close study of the technique 

 and should be attempted only by those who are willing to be 

 disappointed at first. When the techniques have been mas- 

 tered it is a most efficient and satisfactory way to grow large 

 yields of excellent plants. 



Several water-culture systems have been devised, and 

 often named for the man or institution making them popu- 

 lar. "Soilless Gardening" by Gericke uses the water solu- 

 tion, in shallow tanks or troughs, with the plants supported 

 in a seedbed of vegetable material on a wire support. The 

 seedbed and an air space between it and the solution are the 

 distinctive features of the method, which provides for root 

 aeration, the most difficult problem. The seedbed has a 

 layer of straw or excelsior on the wire, then a layer of finer 

 vegetative material, which will support the plant, hold mois- 

 ture to be absorbed by the roots growing in it, and allow air 

 to pass through it freely to the air-space below. The air- 



