Head-changing (also called head-changing): Any method of cutting off the extended branches of branches or the leading branches of branches and replacing the cut parts with branches under the cut mouth is called head-changing.

The branch at the next level must be cut at the head, which is called cutting branch.

The change of head mainly plays a role in regulating the growth potential and changing the growth direction of branches (or branches).

Changing heads can turn weak into strong or strong into weak.

Replacing the weak with the strong is called "retraction" or "atrophy", and replacing the strong with the weak is called "rejuvenation" or "renewal".

It is more common to change the head for retraction.

Both dormancy pruning and growth pruning will use retraction, but different seasons, different objects and different degrees have different retraction effects, but they all have the effect of inhibiting growth, so we should pay attention to moderation. According to the object, season and degree of retraction, retraction can be divided into the following three categories.

① Retraction of annual and biennial branches.

It is mainly used to inhibit the growth potential or change the growth direction of annual and biennial branches.

Among them, the annual branches must be retracted by secondary branches, and both dormant and growing periods can be carried out. Select qualified secondary branches as cutting branches, and cut off annual branches above the secondary branches. For the retraction of biennial branches, if they are in dormancy, choose annual branches as cutting branches and cut off the extension branches of biennial branches above them; If new branches begin to sprout on the annual branches in the early growth stage, the new branches are selected as cutting branches, and the biennial new branches are cut off above them, which is mainly used for post-flowering pruning of flowers and trees. ② Branch retraction.

Branches in a branch group are usually dominated by their own extended branches or main branches. When retracting, select the weaker branches as cutting branches, and cut off the extended branches or leading branches.

This kind of head change has the effect of compressing the growth potential of this part, and is often used in plastic surgery, especially pruning branches.

③ Perennial branches retract.

If a tree is not pruned for many years, or it is not pruned properly for many years, it will cause problems in the whole tree, especially the uneven growth potential.

And it is often "the stronger the strong, the weaker the weak."

At this time, it is very difficult to retract only one or two-year-old branches. Some big branches must be retracted, that is, perennial strong branches can be cut off above a weak branch, so it is called "strong branch strong cutting (re-contraction) and weak branch weak cutting (light contraction or no contraction)". Relatively speaking, head changing is less used for rejuvenation and renewal.

The method of local rejuvenation and regeneration is to cut off the dominant branches in weak extension branches or branches, and choose strong branches as cutting branches to restore the growth potential of this part; The whole tree should be updated for perennial branches belonging to skeleton branches. At this time, if there are no strong branches left under the kerf, it is better not to leave weak branches, thus stimulating the germination of adventitious buds.

For the retraction and renewal of perennial branches, the cross-sectional area is relatively large. Therefore, in addition to the dormant period, we should pay attention to the smoothness of the cut surface as much as possible and apply preservatives on the cut surface.