Every winter I prune my fruit trees and as I do I think, 'uuhhh I don’t really know what I’m doing.' So this year I decided to reach out and get some help. I sat down with Russell Norton a horticulture and agriculture educator with the Cape Cod Cooperative Extension and started by asking him: why do we prune?
"The why’s a really good question. So we have like a make no cut without a reason type philosophy. And so when you're when you're thinking about pruning, you’ve got to think about why you're doing it. So definitely structural pruning is important and productivity."
When it comes to structural pruning, I was surprised to learn that there are different methods for different species.
"So for apples, we tend to go for the shape that’s called central leader shape," Russell explained. "So one of the first things we try to do is identify the central leader, which would be you know the main trunk from the base where it goes into the ground to the top of the tree. And then we want a system of scaffold branches that go up the tree and are kind of spaced around it."
With stone fruits, it’s different, you don’t want a central leader at all.
Instead of having that central leader, we’re often cutting it and forcing it to produce probably around four major scaffold limbs that go out in different directions.
The reason we prune these types of trees differently has to do with tree hormones. Trees that need a strong central leader, like apples and pears, exhibit what’s called apical dominance, a phenomenon where the main central trunk of the tree controls the growth of all the other stems below it.
"In the bud at the top of a vertical branch, there's a chemical produced by the plant called auxin, and that auxin flows down in that branch and suppresses the buds behind it from growing."
This happens with all fruit trees but is more pronounced in species that need a strong central leader. If you only have horizontal branches, the hormone auxin can’t flow down the tree as easily, and the tree panics and sends up lots of weak vertical stems shooting skyward. When Russell told me this, it explained a problem I’ve been having for years — I’d heard somewhere that horizontal branches produce more fruit, which is true by the way, and so I’d been cutting off any vertical branches on my apples and pears and in response, they’d been sending up dozens of the spindly, unproductive stems fruit growers call waterspouts.
"So you're in this constant battle of encouraging a habit that you don't necessarily want," he said.
The solution, Russell said, is to leave the central leader on the apples and pears and encourage a more gentle vase shape with peaches and plums. This satisfies the plants’ hormonal needs and allows for the growth of more horizontal branches below, which are both stronger and more productive than lots of little vertical branches.
"We generally want something that is at like a 60-to-70-degree angle, so something slightly above horizontal is ideal both for strength from that branch union to the tree but also as far as flower production goes."
Another reason to prune this way is to control disease — especially with stone fruits which tend to get all kinds of infections in our humid climate.
"There’s one particular disease that they get called brown rot, which having that open canopy definitely helps, but we also have another disease called black knot and that is a disease that causes cankerous and odd growth and the main way we actually manage that disease is by pruning it out."
This means cutting below the characteristic swollen black stems to encourage new, healthy growth. There’s a lot to remember with pruning but as I’ve learned the hard way, also a lot of good reasons to get it right. And the time, Russell reminded me, is upon us — so if you’re growing fruit trees the next couple months is when you want to pick up those shears:
"I think any time after the New Year is reasonable," Russell clarified. "Wounds that are created in late winter or early spring heal faster than wounds that are created in the fall, so we generally lean towards late winter as the ideal time."
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