CONSTRUCTION NOTES 291 



the seed, nor too closely before or afterwards, because of the danger of the 

 strong solution of the fertilizer coming in contact with the newly germi- 

 nated seedling. It has been recommended that as much as thirty days should 

 elapse between the time of seeding and fertilizing with commercial fertilizers, 

 but that will not always be possible. 



Bone meal is not open to the objection just raised against chemical 

 fertilizers in regard to their scalding or other injurious effects upon young 

 grass plants. It may be applied at any time, either to new or old grass, 

 and is rapidly growing into such favor that it is becoming the most impor- 

 tant of the organic commercial fertilizers. The availability and, therefore, 

 food value of bone meal depends largely upon how finely it is ground, and 

 for immediate effects pulverized steamed bone should be used. As much 

 as 25 pounds to each 1,000 square feet of lawn or 1,000 pounds to the acre 

 of bone meal may be used when seeding a lawn, and since it contains from 

 three to five per cent of nitrogen and 1 8 to 20 per cent of phosphoric acid 

 it supplies all the phosphoric acid needed and a large part of the nitrogen. 

 It also contains a so-called bone phosphate of lime and tends to correct 

 soil acidity. Bone meal is considered to be most useful in sandy or gravelly 

 soil. It should be particularly noted that fertilizers cannot take the place of 

 humus or lime or underdrainage and they give their full value only when 

 these other three factors are properly adjusted. See also the discussion 

 under Types of Fertilizers for Lawns in Construction Notes XV (Landscape 

 Architecture, July 1925). 



Tillage and grading. Before the seeding is done the lawn surface must 

 be thoroughly tilled, and this should not be undertaken until the under- 

 drainage and grading is finished. If possible, this should be at such a season 

 that the grass seed may be sown in the spring before hot weather or in the 

 autumn at the usual season for seeding lawns, as discussed farther on. 

 When the grading is finished there should be a layer of topsoil over the 

 whole area of lawn, which is quite uniform in depth and in composition. 

 This will ensure the appearance of the lawn against spottiness due either 

 to patches of different grasses appearing on different soil types in a large 

 lawn, or to shallow patches of topsoil. A large saving in topsoil may often 

 be made by bringing the subgrade of a lawn to a uniform depth below the 

 proposed finished grade. This should be done by filling up the low spots 

 in the subgrade with soil of good composition. It is often expedient or 

 necessary to strip all the existing topsoil from the area to be made into 

 lawn, before starting any grading operations. This is advantageous for two 

 reasons: (i) it allows bringing the subgrade to a uniform depth below fin- 

 ished grade so as to secure economy in topsoil, and (2) it permits com- 

 posting the topsoil while it is in piles and thus gives an opportunity to 



