4 BULLETIN 479, U. S. DEPARTMENT OF AGRICULTURE. 



by capillarity. A subsoil of hardpan is to be avoided because it does 

 not allow good drainage and tbe moisture retained may cause sour- 

 ing of the soil and excessive freezing and heaving. 



AMOUNT OF LAND AVAILABLE. 



The future development of a nursery can seldom be forecasted. 

 After the nursery is established the location, soil, or some other fea- 

 ture may be found to make it especially suitable for the growing of 

 certain species of trees; the stock may have to be retained in the 

 nursery longer than was anticipated; wider spacing may prove 

 advisable ; longer rotations of crops may become necessary ; or a por- 

 tion of the area may have to lie fallow longer than was expected. 

 Any of these conditions will make extension of the nursery area 

 desirable. A location should be chosen, therefore, where there is an 

 additional contiguous area of good soil lying in such a position 

 that the watering system can be readily extended to it. 



SLOPE AND EXPOSURE OF SITE. 



The nursery site should be as level as possible, because of the 

 danger that the soil on a slope will wash during severe rains or arti- 

 ficial watering. Of course, grades can be lessened by terracing. This 

 is expensive, however, and on terraced areas plowing and harrowing 

 are carried on with difficulty, and protection ditches are almost in- 

 dispensable. Under no circumstances should the slope exceed 5 per 

 cent, and even such a slope is excessive where irrigation is to be 

 practiced. 



On slight slopes the exposure is of little import. There is but little 

 difference in the temperature, frost danger, or length of growing 

 season of the different aspects. On steeper slopes, north, northeast, 

 and northwest aspects are more suitable for nursery purposes than 

 south and west, because of the smaller range of temperature. Frost 

 danger is greater on the south and w^est slopes than on the others, 

 because the plants normally start growth sooner and continue it later. 

 Alternate freezing and thawing, which causes heaving, is more de- 

 cided on south and w 7 est slopes than on the other three. So-called 

 frost holes, or depressions in which the air drainage is poor, and 

 narrow valleys or canyons, should be avoided entirely because of 

 frost danger. In general, a higher location should be given prefer- 

 ence over a lower one. 



ACCESSIBILITY. 



The relative importance of accessibility to base of supplies and 

 labor or to planting sites depends upon whether the nursery is large 

 or small. If it is small and the amount of labor and supplies neces- 



