CHILDREN'S GARDENS 161 



quantities to get the results desired in the plants. 

 These are: 



Nitrogen Phosphorus 



Potassium Calcium 



These can be bought and added to the land where 

 needed. They are a great help in bringing misman- 

 aged land back into fertility. But we can waste 

 money and destroy the soil's power to furnish plant 

 food, if we neglect to have plenty of humus, air and 

 water, suitably mixed with the fine rock. 



Some of the commercial fertilizers ^ which supply 

 these elements are: 



Nitrogen : Nitrate of soda. 



Sulfate of ammonia. 



Refuse from slaughter houses. 



Prepared sheep manure. 



Potassium : Sulfate and muriate of potassium. 

 Phosphorus : Phosphate rock, raw and treated 

 with acid. 



Ground bone. 



Calcium : In the above, and in lime, and oyster 

 shells. 



Greenhouse men generally use fine ground bone meal 

 and sheep manure. 



Reference books for older children who want to be 

 commercial growers : 



