338 



THE CULTIVATED EVERGREENS 



inch layer of soft-coal cinders. The depth of the peat and sand 

 mixture need not be more than eight to twelve inches. A per- 

 manent mulch of oak 

 leaves will help main- 

 tain a proper degree of 

 moisture, and by de- 

 composition will add to the 

 peat supply. If the materials 

 for the mixture are available 

 in quantity, a bed may be 

 laid down over the whole 

 surface of the ground. 



A sharp distinction should 

 be made between half -rotted 

 oak leaves and the ordinary 

 compost of leaves with ma- 

 nure, garden soil, and garden 

 trash. Such a compost is 

 neutral or alkaline in reaction 

 and should not be used on 

 acid-soil plants. Sugar maple, 

 elm, and linden leaves rot 



96. Injurious effect of ordinary rich garden 

 soil on a rhododendron. — Half natural size 



rapidly and so soon reach the alkaline stage that they are not 

 desirable for acid-soil planting. Oak leaves, especially red oak 

 leaves, rot slowly, and in two or three years, if the pile is turned 

 over several times, make a good substitute for upland peat.* 

 No manure, lime, or wood-ashes should be applied to ever- 

 greens that require an acid soil, for all these substances tend to 

 neutralize the necessary acidity. Cottonseed meal, ground 

 soybeans, and spent malt, all of which contain a large amount 

 of nitrogen in organic and acid form, are excellent fertilizers 



*For a more extended discussion of the decay of leaves and its relation to acid 

 soils, see "The formation of leafmold," Smithsonian Rept. for 1913, pages 333-343. 



