There is much to learn yet regarding the behavior of the different
roots under varying conditions when used as stock for the almond, but
sufficient information has already been gathered to permit of certain
recommendations being made.
_Almond Root._—The greatest proportion of almonds in this state are
on almond roots. Where the most desirable soil, moisture and drainage
conditions exist it is best to select the almond root. It will live
in comparatively dry soils, but cannot be expected to make a tree of
large size or bear crops of nuts if the dry conditions continue. Where
irrigation is not available, and the soil is deep and of proper texture,
sufficient moisture may be retained in most years by cultivation to
enable the tree to grow and bear fruit. When extra dry years come, the
almond root may not enable the tree to grow or produce any better than
would another kind of root, but it will carry the tree over a few dry
seasons as well or better than any other. Then, when sufficient moisture
does come, the almond root is ready to start the tree off in its normal
course with the least loss of time.
[Illustration: Fig. 4.—Languedoc almond on peach[3] root; typical of
other trees in same orchard, near Davis. Planted about forty-seven years
before. Compare with trees in same orchard on Myrobalan root, as shown in
Fig. 5.]
The bitter almond is often recommended as being superior to the sweet
almond as a stock. This claim has never been proved. Experiments indicate
that there is fully as much variation between the bitter almond seedlings
grown from seed from different trees as there is between seedlings from
bitter and sweet almonds. Both are equally subject to attack by gophers.
The grower’s chief object, therefore, should be to secure as healthy,
vigorous trees as possible whether they be on sweet or bitter almond
roots.
_Peach Root._—Where the soil moisture is quite variable in different
portions of the soil, or variable from time to time during the growing
season, the peach root will probably be most satisfactory. Soils less
than six or eight feet deep, or where gravelly or hardpan layers occur
at less depths, are not satisfactory in most cases for the almond root,
and under these conditions the peach root is better. The peach root is
a little better where irrigation is practiced during the summer, and
especially so where there is danger of slow drainage of excess water
from the soil. The peach does not thrive with standing water around
its roots, but will better withstand fluctuating or temporary extremes
in water supply than the almond. Its union with the almond is entirely
satisfactory. See figure 4.
[Illustration: Fig. 5.—Languedoc almond on Myrobalan root, typical of
many other trees in same orchard, near Davis, planted about forty-seven
years ago. Compare with trees planted same time on peach root as shown in
Fig. 4.]
_Davidiana Root._—Within the last five or six years the United States
Department of Agriculture has introduced the seed of a Chinese peach,
_Prunus davidiana_, the root of which is more resistant to alkali than
the ordinary peach. This has been found to unite readily with the almond,
although experiments have not yet gone far enough to fully determine its
true value. It gives promise, however, of being a very desirable stock
for sections where alkali may be troublesome.
_Undesirable Roots._—The Myrobalan plum has frequently been recommended
as a stock for the almond on poorly drained soils. The two make a strong
union, but the plum root grows much slower than the almond top, as
indicated in figure 5. A comparison with figure 4, in which both trees
are 48-year-old Languedoc, shows that the trees on Myrobalan root are
pinched-in below the union while those on peach root are swollen at the
base. Even young trees show the same pinching-in below the union. Almond
trees on Myrobalan root do not make as large trees nor do they bear
satisfactory crops in any portion of the state where it has been possible
to compare them with the same varieties on other roots in similar
situations.
The apricot is occasionally recommended because of its strong, thrifty
growth, but it is a mistake to attempt to use it, as the union is not
satisfactory. The trees grow thriftily for awhile, but before they reach
full bearing they either break off at the union or are blown over above
the union by moderate winds.