Like one or two other fruits, Plums produce growths intermediate between extension shoots and spurs, termed, from want of a better name, stubs. Anyone who examines an established tree is likely to find three distinct classes of growth, the first being extension shoots, the second stubs, and the third spurs. Extension or growth shoots, usually quite destitute of fruit buds, or at the most having one or two, are more prominent in young than in old trees. When the grower is making a start with young Plum trees he has plenty of shoots under his eye; in fact, the chances are that he sees a good deal too many, for the Plum is a gross tree. The remedy for excessive vigour is root pruning, which will be dealt with in a subsequent chapter. For the moment it will suffice to deal with the branches.
The exact method of dealing with growth shoots, like A in Fig. 15, depends on circumstances. If the tree is well furnished with them, they should be left untouched, and will then merely extend at the tip; but if the tree is quite young and unfurnished, they may be shortened so as to cause others to break. When a tree is well furnished with growths similar to B, much cutting back is a mistake, for it only multiplies shoots to such an extent that the tree is greatly overcrowded, and consequently fails to bear well. There is a good natural extension shoot at d, and fruiting growths at g, while stubby shoots like f will, if slightly shortened, or even left intact, quickly bear.
This shoot f being a typical Plum growth, may be followed up to a later stage, as at D. It has developed into a, long spur. Now such growths as these give a tree n somewhat tangled appearance when it is full of them, and many pruners with a great love of neatness might shorten them to the point indicated by the bars; but this at least may be said: A tree well furnished with them is a sure fruiter, while one without them is a very poor bearer. Cherish, therefore, in the Plum short, stubby growths which show no indication of extending into long branches, for sooner or later they will yield good fruit.
Growths like C are also eminently desirable. They are spurs that have formed as a natural consequence of keeping the tree open and allowing the moderate quantity of healthy wood retained to mature. Growth shoots pushing from these spurs are not likely to be very strong, and may be shortened to six good leaves in summer, and spurred back in winter.
In connection with Apples, Pears, and Plums alike - indeed, all the principal fruits - the following may be established as a leading point in pruning: That when once the framework of a tree has been formed, the treatment of extension shoots must be modified. Leading shoots need only be cut back when it is desired to originate more branches. If no more branches are wanted - if, indeed, there is a risk of getting too many - do not shorten the leaders. On the lower part of a leading shoot there are often growths which might be termed sub-leaders. Now if the leaders be shortened fresh growths will break in the immediate neighbourhood of these subleaders, and the consequence is that a tangle of shoots is created, which makes for barrenness rather than fruitfulness. If the leaders have to be shortened, then the sub-leaders ought to be cut close in, to prevent the overcrowding foreshadowed. The idea of pruning that prevails in many quarters is that every young extension shoot, whether it be pushing from the top or sides of the tree, and whether or not there be "sub-extensions" on the lower portion, must be cut back to a certain level. This is wrong, and frequently does great harm.
A, one year shoot: a, blossom buds; b, wood buds; c, point of shortening to originate growths.
B, one and two years wood: d, extension shoot left entire or shortened to originate growths; e, subsidiary shoots left entire for forming branches, or where not desired shortened to form spurs; f, short side shoot with fruit buds left entire to produce some fruit; g, very short side growths with blossom buds left intact; h, a natural spur.
C, portion of three years wood of fruitful tree: i, points where fruit has been produced; j, spurs.
D, part of a three years branch: k, short side growth after bearing fruit, marked for shortening to keep spurs close to branch; l, very short side shoot, marked for shortening to prevent elongated spur; m, portion of subsidiary shoot left entire, showing natural spur formation.