Nectarines can be grown in dwarf form in exactly the same manner employed for peaches.

THE PLUM

In all the old books it is said that dwarf plum trees are secured by working on Myrobalan stocks. This statement is hardly true according to our present standards, and is certainly far from satisfactory. This rule came into vogue at the time when only large growing Domestica plums were propagated in this country and the stocks used were mostly either "horse plums" or Myrobalan. The Myrobalan stock does give a somewhat smaller tree than the old fashioned horse plums; but this Myrobalan stock has been for many years the one princ.i.p.ally used for propagating all kinds of plums in America. It has come to be looked upon as a standard rather than a dwarf stock. When we think of dwarf trees, therefore, we expect to see something smaller than what will grow under ordinary circ.u.mstances on a Myrobalan root.

The Americana plum, already mentioned, is a first-rate stock in nearly all respects except that it can not be bought so cheaply as the Myrobalan. It is now grown to a considerable extent by nurserymen in Minnesota, Iowa and the neighboring States. If grafted, or budded early, all varieties of plums take well upon it. The trees on Americana roots make a good growth in the nursery and are easily transplanted. The tree produced on this stock is only moderately dwarf. Still this dwarfing effect is always well marked, this result being shown by the overgrowing of the cion. The top thus appears to outgrow the root, and such trees are apt to blow over during wind storms. Suitable precautions should be taken to guard against damage of this sort.

Prof. A. T. Erwin of Iowa writes on this subject as follows:

"Regarding the Americana as a plum stock, I would state that we are using it by the thousands out here; in fact, have about quit using anything else. As a stock for the European and j.a.panese sorts, it does dwarf them, and the cion tends to outgrow the stock at the point of union, causing an enlargement. The union is also not very congenial, and they frequently break off on account of high winds.

However, in my experience and observation, this is not the case when the Americana is used as a stock for Americana varieties. It does not dwarf the trees seriously and the union is splendid. It is by all odds the best stock we have for plums, and since we do not grow anything but Americana varieties, it works first rate. It does tend to sprout some, though there is little trouble in this regard after the trees come into bearing."

[Ill.u.s.tration: FIG. 8

THE WESTERN SAND CHERRY

_Prunus pumila besseyi_]

The sand cherry seems to be the dwarfing stock par excellence for the plum. This sand cherry is a heterogeneous species, or as some botanists think, is three species, ranging throughout the Northern States from Maine to Colorado. The narrow leaf upright form growing about five feet tall, known as _Prunus pumila_, is found along the Atlantic coast. The broad leafed dwarfer form known as _Prunus pumila besseyi_ or _P.

besseyi_, is found in the Western States. Another rarer form of more irregular growth known as _Prunus pumila cuneata_, or as _P. cuneata_, is found in the North Central States.

[Ill.u.s.tration: FIG. 9--UPRIGHT CORDON PLUM

With buds set into the naked trunk]

All of these different forms may be used for propagating plums or peaches. The western form (_P. besseyi_) (Fig. 8) is in some respects the best, producing the dwarfest and apparently the best trees. In our experience, however, nearly all varieties of plums and peaches give a better stand of trees when budded on _P. pumila_. _Prunus cuneata_ is inferior to the others.

The eastern form, _P. pumila_, has another advantage from the standpoint of the nurseryman in that it is more easily propagated from cuttings.

For the most part the western sand cherry is propagated from seed. Both forms can be propagated from layers.

NURSERY MANAGEMENT

Dwarf trees are managed in the nursery very much the same as standards of the same varieties. There are no special points to be observed except in the formation of the tops. Western New York nurserymen, who now grow the princ.i.p.al supply of dwarf apple and pear trees, have the custom of forming their nursery stock with high heads. That is, the heads are formed at a height of eighteen inches to three feet from the ground. In this matter the pattern is taken after the usual style of standard trees. This is quite wrong. Of course, some planters might like to have dwarf trees with trunks two or three feet tall, but the best form has a much shorter stem. At any rate the buyer of dwarf trees ought to be at liberty to form the head within three or four inches of the ground if he so desires. This becomes very difficult if the tree is once pruned up to a height of two or three feet.

In order that the planter may reach his own ideal perfectly in this matter, it is sometimes necessary to buy one year old trees, what the English nurserymen call maidens. This, of course, enables the tree planter to form the head wherever he desires.

IV

PRUNING DWARF FRUIT TREES

The pruning of dwarf fruit trees is a matter of the greatest consequence, for on proper pruning depend both the form and the productivity of the trees. Some of the details of management will be explained in the succeeding chapters, dealing with the particular kinds of fruits, but a few general statements should be set down here.

1. The trees are severely headed in. This applies more particularly to bush and pyramid forms. By the term "heading in" we refer to the shortening of the leaders. Such shortening is usually given at the spring pruning, while the trees are dormant. The leaders may be headed in at times, however, during the latter part of the growing season, in July. Such stopping of growing leaders will be practised more often on young trees just coming into bearing than on old trees. (Fig. 10).

Constant heading back of some sort, however, is required in nearly all cases, if the tree is to be retained in its dwarf form. The mistake has often been made of thinking that a tree propagated on a dwarf root would take care of itself.

2. Summer pruning is essential. In most American orchard practise one annual pruning (sometimes one pruning every five years!) is considered sufficient, and systematic summer pruning is seldom or never given. Now summer pruning tends much more to repress the growth of a tree than winter pruning does. In fact, heavy winter pruning leads rather to increased vegetative vigor. Aside from any special system of pruning, therefore, this rule is to be remembered, that summer pruning is desirable, on general principles, for dwarf fruit trees.

[Ill.u.s.tration: FIG. 10--BUSH APPLE, THREE YEARS OLD

Showing strong leaders formed during the summer]

3. Side shoots usually need pinching during the growing season. Leaders are more frequently allowed to grow unchecked throughout the season, or are stopped only late in their period of development. In the pomaceous fruits, which form distinct fruit spurs, the checking of these side shoots helps toward the production of fruit buds. As long as every bud is allowed to push out into a strong shoot no fruit spurs can become established. Thus the summer pinching of the side shoots on apples and pears has the purpose of encouraging the formation of fruit spurs. On peach and plum trees equally distinct fruit spurs do not form; but if the side shoots are allowed to push forth unrestricted they are apt to choke one another. There will be too many of them, they will not get light enough, their growth will be weak and sappy, and they will not form fruit buds. Good fruit buds on a peach tree, for example, form on strong, clean, healthy shoots of this year's growth for next year's crop of fruit. It is seen, therefore, that in nearly all sorts of dwarf fruit trees the summer pruning is especially directed to the suppression or regulation of the growth of side shoots.

This part of the treatment becomes of prime importance in dealing with cordons and espaliers.

4. The control of the fruit spurs or of the side shoots here contemplated requires that the trees be gone over more than once during the growing season. In fact, four successive examinations of the tree are usually required. Old trees can sometimes be managed with two or three, but young ones, on the other hand, will sometimes require six or more. Of course, there are usually only a few shoots that need attention at each succeeding visit, and the work can be very rapidly performed.

The first pruning, or pinching, falls about three weeks after the trees have started into growth. The next one comes ten days later, the next one ten days later again, and the fourth pruning two weeks after the third. From this time onward the intervals lengthen. These specifications, of course, are only approximate and suggestive. Some judgment is required to select just the proper moment for pinching back a shoot and even more to select the time for a general summer pruning.

Those trees which enjoy the sympathetic presence of the gardener every day are sure to fare best. The bulk of this pruning can be done with the thumb nail and forefinger, but I find a light pair of pruning scissors pleasanter to work with.

5. Root pruning is sometimes advisable. Since the whole program is arranged to check the growth of the dwarf tree, root pruning would naturally fit well with the other practises recommended. Root pruning checks the growth of a tree about as positively as any treatment that can be devised. When dwarf pear or apple trees seem to be making too much wood growth and not enough fruit, they can be taken up, as for transplanting, during the dormant season and set right back into place.

This digging up and replanting is always accompanied by some cutting of roots. The whole root system is disturbed and has to re-establish itself before the top vegetates very strongly once more. Such root pruning ought to be done late in the fall. It is a special practice, suited to refractory cases, and the gardener is not recommended to indulge in it too freely.

[Ill.u.s.tration: FIG. 11--BUSH APPLE

Three years old, before pruning]

[Ill.u.s.tration: FIG. 12--BUSH APPLE

Same tree after pruning]

6. A certain equilibrium between vegetative growth and fruit bearing should be established at the earliest possible moment, and should be maintained thereafter. Of course, some such equilibrium is sought in the management of a standard tree; but it is secured earlier in the life of the dwarf tree and should be much more accurately maintained. The tree must make a certain amount of growth each year, but this must be only enough to keep it in good health, and to furnish foliage enough to mature the fruit. Beyond this wood growth the tree should bear a certain amount of fruit every year, for annual bearing is not only an ideal but a rule in the management of dwarf trees. This equilibrium once established must be maintained not by haphazard pruning, but by some suitable system. If there is the proper balance between summer pruning and winter pruning, combined with proper control of cultivation and fertilization, then the balance between vegetation and fruitage can be kept up. It is a delicate business, like courting two girls at once, but it can be carried out successfully.

7. The training of trees into mathematical forms is largely a mechanical process. For the most part the trees are shaped while they are growing.

The young shoots are twisted and bent to the desired positions, and are tied into place until the stems become hardened. There are many clever little tricks for expediting this sort of work and for making the results more sure, but a rehearsal of them here would be tedious. The most important rule to remember is that constant attention must be given the shoots while they are growing. Mistakes are corrected with difficulty after an undesirable form has been allowed to harden.

[Ill.u.s.tration: FIG. 13--CORDON PEARS

Before pruning]

[Ill.u.s.tration: FIG. 14--CORDON PEARS

After pruning]

V

SPECIAL FORMS FOR TRAINED TREES

We have already explained the connection between dwarf trees and the practise of training them in special forms. It is true that this practise looks childish to American eyes. It seems to be only a kind of play, and a rather juvenile sport at that. Nevertheless we should understand that in some parts of the world it is a real and profitable commercial undertaking. We should consider also that in other places, where fruit of very high quality is better appreciated, perhaps, than it is in America, the extra trouble is thought to be worth while for the superior quality which it gives the fruit. As this matter is coming to be of more importance in America also, and as the interest in amateur fruit growing is enormously increasing, we may fairly begin to talk about these methods.