"Heading back" is one of those terms that means something quite different in a horticultural context than it does in everyday life (where it indicates movement, as in returning to a particular location). When talking about plants (pruning, specifically), it means pruning off the terminal or "head" growth of a tree or shrub branch down to just above a lateral bud. "Lateral" means "side," and a lateral bud is one that grows from a node along the side of a branch.
You will typically use pruners to make this cut.
Here is an example of how the term is used in a sentence (from Floridata.com):
"Heading back the terminal shoot of a young tree will cause the leader (main trunk) to branch - but note that you may get more new leaders than you want, so be ready to thin out the extras."
Heading back is a type of pruning cut, but it is only one kind. To help beginners better understand the meaning of the word (and why it is important to know it), it will be helpful to take a look at the other types, so that differentiations can be made and reinforced.
Types of Pruning Cuts
Besides heading back, you will see the following kinds of pruning cuts referenced in books and on websites about landscaping and gardening:
Pinching requires no tools (such as pruners). Instead, you literally "pinch" off the growth at the top of a plant's stem, using your fingers.
As with heading back, thinning requires the use of pruners or some other cutting tool, such as a bow saw. But the similarity largely ends there; these two pruning operations are undertaken for very different reasons.
As an example, let's take a thinning cut to be made on a tree. When making such a cut, prune off the whole branch in question -- whether it be back to the trunk or back to a scaffold branch. Why would you prune off such a branch? Well, you may wish to open up the canopy of a tree (that is, create more space between the branches, just as when you "thin out" vegetable seedlings to increase the space between them), or perhaps the branch is rubbing up against another one (in which case it is best to determine which branch you would rather keep and remove the other one).
Thinning cuts are also commonly made on shrubs -- sometimes for the same reasons. In addition, sometimes you can reinvigorate a shrub by entirely pruning out some of the older branches, thereby "passing the baton," as it were, to the newer branches. The energy that would have gone into the older branches is better put to use in the younger, more vigorous ones, which thereby grow even more vigorously. For example, I often make thinning cuts on my forsythia shrubs for this reason. Homeowners who have a vague feeling that they should be pruning a specimen shrub (but who do not know precisely why, or how to go about it) will most often be better served by making a thinning cut on it rather than by heading it back.
Shearing is most commonly practiced on topiaries and hedges, such as those formed by boxwood shrubs. I like to use a cordless hedge trimmer for the procedure. The average homeowner who has not studied horticulture probably finds this type of pruning cut easiest to understand. Clearly, the purpose behind shearing a hedge is to:
- Keep its growth within the desired bounds
- Make the hedge as dense as possible by stimulating new growth
What Is the Purpose Behind Heading Back?
I have talked about the purposes behind pinching, thinning, and shearing; now it is time to reveal why one might wish to practice heading back. How is it similar to these other pruning operations? How is it different?
The critical contrast to comprehend here is that between a thinning cut and a heading cut. Heading back a branch on a shrub will produce side shoots, thereby making the shrub's growth denser (it is like pinching and shearing in this regard).
Remember those lateral buds I mentioned earlier? When you make a thinning cut, you are removing those buds, so they never have a chance to produce new branches. The result is an airier, more open branching pattern. By contrast, heading cuts preserve the lateral buds and generate new growth (side shoots), filling in the interior of the plant. Be careful: you can spoil the natural shape of a shrub through heading back. So what is an example of a legitimate use of a heading cut? Well, sometimes, we prune not because we want to, but because we have to. This is the case when, for example, a storm snaps the tip of a shrub's branch, leaving it hanging. In this instance, the branch is crying out for a heading cut.
Heading back can also be used to keep a shrub within bounds (as when you have exercised poor plant selection and located a shrub in a spot way too small for it) or alter its shape. Regarding the latter, you can sometimes cut above a bud facing away from the center of the shrub to generate growth in said direction. This knowledge can come in handy if you are trying to correct the shape of a bush that has suffered damage or that has not been properly cared for in the past.
In my photo, I show where I would make a heading cut on my Sky Pencil holly. The habit of this shrub is columnar, and heading back the plant will not spoil its natural shape -- it will simply keep it shorter and bushier. The area that I have circled in the photo is where the leaf node is. By pruning just above it, I will stimulate new growth. Because of Sky Pencil's rigidly upright growth habit, the new branch thus generated will stick straight up, rather than out to one side or the other. There is a node on each side of the branch, so I can cause two branches to grow with my cut where, before, there was just one branch (thus making the shrub bushier).
Where to Go From Here
Do you need more help with shrub care? Check out my resources on caring for garden shrubs.