The long-needled pines like Ponderosa and Austrian Pine tend to grow large end shoots with many needles. Selectively trimming needles off can help balance shoots, weakening strong ones and strengthening the smaller ones.
Typical Ponderosa pine branch with a fat end bud on the main shoot (left) and 2 smaller shoots back down the branch (right). The needle production on the main shoot overwhelms the needles on the smaller shoots, which tends to perpetuate.
Trim some of the second year needles off in late summer or early fall. If Ponderosa needles are pulled, often a patch of cambium will come off. Pulling a single needle at a time can often prevent this, but I usually just cut them off one bundle at a time. The stub that remains browns and falls off.
Side view after needle trimming.
Top view. The trimming of old needles (second year needles, not this year’s) gives the smaller shoots (which receive no needle trimming) a leg up. The idea is that over time these shoots will be encouraged and their buds will get fatter, producing more needles. Eventually all shoots will make the same number of needles.
Overview of work. The circles show where needle bundles were cut. Several old needles were left to create possible needle buds, shown by arrows. These potential buds can become shoots and later branches. By trimming selectively we can choose where potential shoots arise, our future branching pattern. Notice the sheath color on the needle bundles. The old ones are white, this year’s are brownish. Many single flush pines, like Ponderosa, are stronger if at least some second year needles are left.
You may use this technique on any pine, though small-needled pine needles are often pulled rather than trimmed off.
Especially on species that grow few branches, pruning is often not an option and we need to use all the available branches. Needle trimming is a soft technique that over time may offer a path to reining in strong growth.
To sum up, selective needle trimming does two things:
- sets up the possibility of a needle bud between the needles where a bundle is left, which grows a new shoot
- balances the pine shoots, which if applied homogeneously over the whole tree can help correct top to bottom imbalances as well