Q. I am planting a 15-gallon ‘Wonderful’ pomegranate and
suspicious if the plant would benefit from a deeper hole amended with washed
sand to help with drainage.
A. Unless there is a drainage problem, 99% of the time
there is no benefit from digging a hole deeper. There is even less benefit when
adding sand to the hole in any form and this practice is likely to make drainage worse! When drainage
is a problem, the simplest method is to plant on mounds.
The
majority of small tree or la
rge shrub roots are about 18 inches deep. That’s
all. But the soil they are planted in must drain water or the roots will
suffocate or “drown”. To check for drainage, dig a hole to the same depth as
the 15-gallon planting container. Fill the hole with water and let it drain. Fill
the hole a second time and watch how fast it drains. Filling this whole a
second time is very important because the first filling only measures how fast
water enters the soil or its “infiltration rate”. Filling the same hole a
second time, when the soil is still wet, measures true drainage or its
“percolation rate”.
If the
water in the hole drains overnight, its drainage is acceptable. Only very
shallow rooted plants like lawns, vegetables and annual flowers are watered
daily during the summer months. When watering trees and shrubs the soil should
be drained for at least one day between irrigations. This gives they soil and
roots a chance to “breathe” before the next irrigation.
Take my
word on this but adding sand to a planting hole, either as a layer or mixed
with the existing soil, is a recipe for disaster. Adobe bricks are made from a
mixture of soil, sand and organics. Keep that in mind.