44 BULLETIN 816, U. S. DEPARTMENT OF AGRICULTURE. 
varieties used for street purposes. With such varieties as elms 
sycamores, and some southern oaks, somewhat larger trees can be 
used equally well, while smaller trees would be better in the regions 
of limited rainfall both east and west of the Rocky Mountains and 
for tulip trees and sweet gums, especially in the northern portion of 
their range of usefulness. 
PREPARATION OF HOLES. 
Next to the selection of a proper variety, the preparation of the hole 
is the most important detail of street-tree planting. Because of the 
restricted area available for the spread of the tree roots, and owing to 
the artificial conditions imposed by the improvement of city streets, 
the soil provided for the feeding ground of the roots of the young tree 
must be liberal in quantity and of the best quality. From 2 to 3 
cubic yards of soil should be provided for each tree. It is desirable to 
have at least 18 square feet of opening in the sidewalk, especially if 
it is of concrete or other impervious material. Trees will grow with 
smaller sidewalk openings, but they are not likely to thrive so well, 
and it is impossible properly to prepare a hole for planting a tree with- 
out disturbing at least this much surface soil. The proper depth of 
soil is from 24 to 3 feet. A hole 3 feet deep large enough to hold 2 
cubic yards of soil has a surface area of 18 square feet. A hole 
6 feet long, 3 feet wide, and 3 feet deep will hold 2 cubic yards of soil, 
will have the smallest desirable surface area, and will be of such 
dimensions as will best conform to the usual sidewalk and roadway 
widths and thus not interfere with traffic. 
The tree hole must be so drained that water will not stand in it. 
If the soil is so impervious as to hold water some artificial drainage 
must be provided. That portion of the depth of a hole that acts as a 
cistern for holding water is valueless as a feeding ground for roots. 
For every cubic foot of soil in the bottom of a hole that might thus 
be made valueless by standing water, 14 cubic feet of soil should be 
added by increasing the length or width of it. Under no circum- 
stances, however, should the depth of available feeding ground be 
less than 2 feet. The deeper the roots may be encouraged to grow, 
the less injury is likely to be experienced from drought. 
The soil used should be topsoil from land that has been producing 
good crops. This should be well enriched with rotted manure, one 
part of manure to four of soil. The addition of such fertilizers as 
ground bone, tankage, fish scrap, or cottonseed meal at the rate of 
1 pound to the cubic yard of soil is also helpful Commercial ferti- 
lizers containing mostly phosphoric acid obtained from other sub- 
stances than ground bone are not to be recommended for use in the 
soil about the roots at planting time. When used they should form 
a surface application, worked into the soil after planting. 
