SUGGESTIONS ON GRAFTING METHODS
Grafting, including budding, may be defined as inserting a piece of wood
which carries buds of a desired variety, on a root stock sufficiently
compatible to accept it, for the purpose of propagation. Methods vary,
each nurseryman having one or more which he prefers, but the principle
is always the same.
Scionwood may be cut the fall before grafting is to be done, after the
growing season has ended, but some prefer to cut the scions in early
spring. This means that the scions must be stored until time to graft,
and correct storage is so important that nurserymen make elaborate
provision for it. I have found that keeping scions underground in a
Harrington graft storage box is the safest method. An illustration of
this box is given, with directions for its construction and location. A
small quantity of scions may be kept in an icebox (not a mechanical
refrigerator), by cutting them into convenient lengths of one or two
feet, dipping them in melted beeswax, wrapping them in tar or asphalt
paper and placing them close to the ice. They will remain in good
condition for several months if there is always a good supply of ice.
Care must be taken in dipping the scions in melted wax, for if the wax
is too hot it will injure the buds. It should never become so hot that
it smokes. I find it advisable to keep an unmelted piece of wax in the
liquid wax to hold the temperature down.
Another method of storing scions, after they have been dipped in
beeswax, is to place them on the earth of a cellar floor and cover them
with a few burlap sacks. They should never be allowed to become wet or
they will start to mold. If they are to be stored in this way, a watch
must be kept for mice which will molest them and destroy them if they
have an opportunity.
Although bud wood may be stored in any of the three ways mentioned, it
should not be waxed. Because of this, it is more likely to deteriorate.
It must be examined frequently and if mold is found, the wood should be
dipped in a Bordeaux solution. After drying, it may be placed in storage
again. It is a good plan to wrap bud wood in tar or asphalt paper when
storing it. However, I have found that the best storage conditions for
all scionwood that I have yet discovered is in the use of peat moss.
Peat moss must be on the distinctly acid side in order to perform the
function of storing scionwood. Most peat moss is generally acid; however
the simple litmus paper test with which every high school pupil is
familiar, can be made. Having acquired good acid peat moss, dampen a
sufficient quantity to pack the scions in to give them liberal
protection. Do not make the bundles of scionwood too large, from 10 to
20 scions in a bundle is better than a large number and much easier to
handle. The moss should be prepared exactly the same as advised in
storing chestnuts (see chapter for storing seeds). In this case it is
not necessary to wax the scions at all. The moss should be applied by
sifting it into the open spaces between the scions and a larger wad at
the base of the cuttings, not at the terminal or bud ends as these would
be better left unpacked. The package is now rolled into a cylinder,
using tar paper or asphalt treated paper, and both ends left open. Do
not use ordinary paper or wax paper as it will turn moldy. Cylinders of
tar paper containing the packed scions should be placed in a damp room
like a cellar with a dirt floor which is cold enough to keep potatoes
and other roots in good condition throughout the winter. If the cellar
is not a good storage cellar for roots and herbs it will not be good
enough for the scionwood as it will be too warm generally. Neither
should they be frozen solid, therefore if a good root cellar is not
obtainable then these should be put in the Harrington graft box already
described or placed under the sawdust in an icehouse and close to the
ice. An old-fashioned ice refrigerator will also make a good storage
bin, placing them close to the ice at all times.
[Illustration: Drwg by Wm. Kuehn. _Making a scarf with a plane
preparatory to grafting._]
Selection of good scionwood and bud wood, a very important matter, is
made according to definite standards. Some plants graft better if wood
is used that has two seasons' growth, but, in general, wood of the
current season's growth is used. It must have reached its maximum
possible maturity before it is cut. Also, some attention should be paid
to the vigor of the growth which it has made during the season. For
instance, in choosing between wood which has made only two or three
inches' growth and that which has made a foot or more of growth, both
being equally sound and mature, the more vigorous should be chosen.
Attention should be paid to the development of the buds, which should be
plump and never immature.
It is advisable to label scions before they are stored to avoid the
confusion that will result if they are mixed. I find that the best
method of doing this is to get a sheet of zinc, from 20 to 30 gauge
thick, and cut it into strips one inch wide by one and three-quarters
inches long. I bore a small hole in one corner of each tag, through
which I thread 18-gauge copper wire, doubled and with the bottom loop
folded over (see page 40). In preparing these tags, it is important to
remember that both wires must pass through the hole in the metal tag,
otherwise, the slight movement due to winds will cause the metal to wear
through. Two wires prevent this action indefinitely. Since a small wire
cuts through a zinc tag in one or two years, heavy wire must be used.
Wire such as I have indicated is satisfactory. I print the necessary
information on each tag with a small, steel awl, and such labels are
still legible after twenty-five years. Copper, brass or aluminum would
also make good tags, but these metals are more expensive. Of course,
these tags may be used for small trees as well as grafts and scionwood
and it is always well to do a good job of labeling all work, since many
errors may result from disregard to this important detail.
In the north, the time to graft nut trees is when the cambium layer of
the host, or stock, is active, which is usually during the entire month
of May. This cambium layer consists of those cells lying just inside of
the outer bark, between it and the woody part of the tree. When these
cells are active, the inner side of the bark feels slippery and a
jelly-like substance can be scraped from it. Although this is the state
in which the stock should be for grafting, the condition of the scions
should be almost the opposite, rather dry and showing no signs of
cambium activity. The bark should cling firmly to the woody part of the
scions, whereas the bark of the stock should slip off readily. Another
good and fairly satisfactory rule is never to graft the stocks of nut
trees until after the young leaves appear.
In grafting young nursery trees not more than an inch in diameter, the
whole tree is cut off at any distance from the ground convenient to the
nurseryman. Sometimes they are cut within a few inches of the ground,
sometimes two or three feet. In my work, I like to keep the scions as
high above the ground as I can. When the top of a stock is cut off,
there is a great deal of sap pressure and the tree bleeds. It is a poor
policy to attempt grafting while this is happening. Rather, one should
cut the tops off, then wait for several days before inserting any
grafts. Tools must be kept very sharp. A good grafting knife is
sharpened on one side only, so that the blade is flat along the side
which lies next to the cut made on the scion when it is trimmed. If
unaccustomed to handling a knife, one can obtain more accurate results
by using a small plane. I do this by holding the scion firmly in my
right hand and pulling it toward me, against the cutting edge of the
plane which is held in the left hand. Illustrations show how this is
done.
The only disadvantage in using a plane is that one must exchange it for
a knife to make the receiving cut in the stock before inserting the
graft. This necessitates exposing the graft to the air for a longer time
than does using a single instrument.
Spring budding is done during the same period as grafting. Bud wood is
usually much larger in diameter than scionwood, for it is easier to
remove buds from big branches than from wood only one-quarter inch in
diameter. When budding is to be done, take along only enough wood for
half a day's work, leaving the rest safely stored. A piece of wood
having a bud is prepared as shown in the illustrations "A" and "B" (next
page). A T-shaped slot is made in the stock to receive the bud, a
process called "shield budding." This is tied in place with either
string, raffia or gummed tape, as shown in "C" and "D" (next page). The
bud must be free to grow, and although it may be covered completely with
wax, no part of the binding material should be close to it. Since it is
not necessary to cut off all the tree in budding, enough of it may
remain above the bud to brace the shoot that develops. Later, it may be
necessary to cut back the tree to the bud so that a callus will form and
cause the wound to heal properly.
[Illustration: Drwg by Wm. Kuehn _Shield Budding._]
Best results are obtained when a graft union is coated with melted
beeswax. Another and cheaper wax may be made by combining four parts of
rosin, one part of beeswax and one-sixteenth part of raw linseed oil. To
this is sometimes added a little lampblack to color the mixture so that
it can be seen on the graft. Again, care must be taken to prevent
injuring the cells with wax that is too hot.
I have used many kinds of tying materials, but the one which gives me
best results is gummed tape, which preparation I describe in another
chapter. By wrapping it in spirals around a graft union, I have a
material which holds the graft in place and at the same time excludes
air. The rubber also seems to encourage the formation of that tissue
which unites the stock and scion. In addition to tape, melted wax should
be brushed into those crevices and cracks which always occur in making a
graft.
It is usually advisable, although not necessary, to shade new grafts. To
do this, cover them with light-colored or white paper sacks. Never use
glassine alone for it causes the grafts to overheat and so destroys
them. Whatever tying material is used, either to fasten on these bags or
to support the grafts, it should be inspected at intervals during the
summer, as it may constrict the graft or stock and injure or cut off the
cambium.
After a scion begins to grow, it must be firmly braced against the force
of the wind, for a heavy gale can rip out grafts made years before.
Laths make good braces for growing shoots. They may be attached to the
main branch by stout waterproof twine such as binder twine, and the
growing graft tied with soft muslin strips to the lath. As the graft
grows more muslin strips should be used to keep the excessive growth
anchored to the lath. Grafts will often make three or more feet in
growth in one season.
It is important to remember that sprouts or buds which start from the
stock must be rubbed off. If they are allowed to flourish, they may
prevent the scion from growing. When working over a tree several inches
in diameter, it becomes an art to keep the tree stock satisfied, yet to
encourage the growth of the scions. In large trees, a few sprouts must
grow to nourish the root system, but this is not necessary if the stock
is one inch, or less, in diameter.