There are indeed some trees which are normally dwarf, so to speak. They never reach a considerable size. They are smaller than other better known and related species. For example, the species Prunus pumila besseyi is sometimes called the dwarf sand cherry, simply because it is always notably smaller than related species. The Paradise apple is spoken of as a dwarf because it never attains the stature which other apples attain.
But in the technical sense, as the term is used by nurserymen and pomologists, a dwarf tree is one which is made, by some artificial means, to grow smaller than normal trees of the same variety.
These artificial means used for making dwarf trees are chiefly three: (1) propagation on dwarfing stocks, (2) repressive pruning, and (3) training to some prescribed form.
DWARFING STOCKS
The most common and important means of securing dwarf trees is that of propagating them on dwarfing stocks. These are simply such roots as make a slower and weaker growth than the trees from which cions are taken. This will be understood better from a concrete example. The quince tree normally grows slower than the pear, and usually reaches about half the size at maturity. Now pear cions will unite readily with quince roots and will grow in good health for many years. But when a pear tree is thus dependent for daily food on a quince root it fares like Oliver Twist. It never gets enough. It is always starved. It makes considerably less annual growth, and never (or at least seldom) reaches the size which it might have reached if it had been growing on a pear root.
This is, somewhat roughly stated, the whole theory of dwarfing fruit trees by grafting them on slow-growing stocks. The tree top is always under-nourished and thus restrained in its ambitious growth of branches, as seen in Fig. 1.
While the tree is made thus smaller by being grafted on a restraining root, it is not affected in its other characteristics. At least theoretically it is not. It still bears the same kind of fruit and foliage. Bartlett pear trees budded on quince roots yield fruit true to name. The pears are still Bartletts, and can not be told from those grown on an ordinary tree. Sometimes the fruit from dwarf trees seems to be better colored or better flavored than that from standard trees; but such differences are very delicate and usually receive slight thought.
FIG. 1—DWARF APPLE TREES IN WESTERN NEW YORK