In the first place, to secure successful results it is necessary to understand clearly what the dynamiting is to accomplish. Some orchardists and farmers have the idea that the purpose of the dynamite is to excavate the hole for the tree and save them the trouble of shoveling out the soil. This is a wrong theory.
The object of dynamiting for tree planting is to break up the subsoil at a depth of from three to five feet so as to create a soil sponge or water-absorbing area twelve or twenty feet in diameter around and underneath the spot where the tree is to stand, so that the heavy rainfalls and melting snow of spring may be conserved in the subsoil to take care of the tree during the long dry summer.
If the force of the dynamite is used merely to blow out the soil and make digging unnecessary, it is unreasonable to expect the dynamite to do this underground work. On the other hand, when the charge is properly placed at a depth of about three feet and tamped in just enough to confine most of the force of the explosion in the subsoil, the blast will not only crack and pulverize the subsoil, but will also break up the ground around the bore hole clear to the surface, and throw it into the air, possibly a foot. It is then a very easy matter to excavate the hole for planting.
Necessary Soil Conditions:
There is no economy nor advantage in using dynamite in a soil that is loose and sandy to a depth of three or four feet. The weakness of this soil is that it allows water to percolate through it too rapidly, hence dynamite would be harmful rather than helpful under such conditions, but no matter how loose the top soil or plowed soil may be, if it is underlaid by more or less impervious clay, or even a heavy loam, dynamiting under proper conditions will certainly increase its water-storing capacity, and also make it easier for the roots to grow downward and deep.
The proper conditions referred to are that the blasting must be done when the subsoil is relatively dry, otherwise it will not crack or pulverize. Every farmer knows the disadvantage of plowing wet top soil. It is equally disadvantageous to blast a wet subsoil. Of course, some subsoils are always in a more or less damp condition and never get thoroughly dried out, but they may be safely and advantageously blasted when they are in their dryest condition.
Water-logged soil should never be blasted except for the purpose of ditching it or tiling it so as to get it into a proper condition for blasting. The ditching may be done economically and quickly with dynamite, and in many cases this will answer just as well as the more expensive tiling. When the ditching or tiling has drained this subsoil, it may then be safely blasted.
Filling the Pot-Holes:
In any heavy soil the explosion of the dynamite tends to form a cavity in the immediate vicinity of the cartridge, varying from one to two feet in diameter. The heavier or the wetter the subsoil, the larger this cavity is likely to be. After the blast the top soil should be shoveled out and laid to one side; next shovel out the subsoil and lay it on the other side of the hole; continue this excavation until the pot-hole is reached, then be careful to fill this hole reasonably tight with subsoil, the object being to prevent the possibility of soil falling away from the roots of a tree after planting, and leaving it suspended in the air. This is the cause of the death of trees planted in dynamited holes which some unsuccessful experimenters report. It takes a little time to fill this pot-hole, but the many advantages of planting trees properly in dynamited holes more than offset this extra time and trouble required to properly prepare the hole.
Planting the Trees: