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  • Sean Dugan

Wait! Don't prune your stone fruit trees yet!

Updated: Feb 27

Some say people only prune stone fruits (peaches, nectarines, apricots, plums, cherries) in the winter. Some say only prune them in summer. So what gives?! When is the right time to prune stone fruits and what can happen if you prune at the wrong time?

Well, I'm going to do my best to explain it in a way that makes sense, so that hopefully you'll have a better idea of when to prune your trees.

The trouble with understanding and teaching pruning "rules" is that they are complex and nuanced. They aren't like straightforward math rules, they are like rules that follow a flow chart with many "except when" and "only if" situations. There are rules though, which tell us the expected response your tree will have based on when and how it is pruned.

Here's an example of the nuance of a rule about pruning stone fruits.

  1. Only prune stone fruits in summer, after harvest. Except when: a. the tree is young (1-3 years old) b. the tree needs structural cuts to remove dead wood, overlapping branches, shorten structurally weak branches that will break with fruit load, etc c. the tree needs renewal cuts to stimulate the growth of new fruit buds

  2. For a, b, and c - prune stone fruits at bloom or just after (early Spring).

The primary reason for the "only prune in summer" rule is that while stone fruits are typically vigorous growers, they are famously susceptible to disease like bacterial and fungal canker which can weaken or kill a tree. Stone fruits are also rather poor at wound healing, so this makes them susceptible to infection after pruning. Apple and pears are good at healing wounds when dormant, so winter pruning of pome fruits is rarely a problem. But stone fruits are the worst at wound healing when they are dormant. Once they wake up and start actively growing, they are much better at healing pruning wounds, and this decreases the likelihood of infection. In summer the tree is actively growing, and in many climates summer is less rainy - and therefore less of a disease spreading time of year.

These are the very valid reasons for the "only prune stone fruits in summer" rule that you hear about. But most trees cannot be managed with only summer pruning, especially young trees. Pruning in early life, especially the first 1-3 years after planting, is the most crucial for making structural cuts to form a good tree structure. It does not work well to only summer prune young trees for structure. Why not?

Pruning done in late winter/early spring is a growth invigorates growth. With heading cuts, we cut back first year growth and the more you cut back, the more the tree grows. Pruning done in summer is de-invigorating. Want your tree to be shorter? Prune it in summer. So for young trees that need a strong structure established, they need late winter/early spring pruning to stimulate strong growth and clarify structure. If you get years 1-3 on track, you have a good shot at having a mature that could be managed with only summer pruning.

But what about the risk of infection with dormant cuts? Where I cut my teeth pruning trees on the central coast of California, pruning stone fruits in winter was regarded as a non-issue. In other words, just do it, don't worry about it. And I think that's perfectly reasonable there. The longer growing season means that trees have more months of sun to gather resources, grow, and have more resilience to disease. They also aren't as deeply dormant. My experience here in Boise, Idaho, is that pruning stone fruits while dormant does lead to a higher incidence of dieback, canker, and disease.

Fortunately, there's an easy solution - which is to prune at bloom or just after. The tree is still dormant enough that pruning at this time is still invigorating, but the tree is starting to leaf out and it does a better job of wound healing. It varies year to year, but late March to early April is a good ballpark.

To think about it another way, here is a stone fruit pruning "key".

Stone fruit pruning key

  1. Is your tree young (planted within the last 1-3 years)? If yes, prune at bloom or just after. If no, proceed to 2.

  2. Does your tree have long, structurally weak branches that make break with fruit load? If yes, prune at bloom or just after. If no, proceed to 3.

  3. Does your mature tree have limited new fruitwood? If yes, prune with renewal cuts at bloom or just after. If no, proceed to 4.

  4. Does your mature tree have a good established structure? If yes, prune in summer.

This key helps determine when pruning in early spring is necessary. In all the situations where you should prune in early spring, you can also do additional summer pruning to help clarify structure.

Do you prune your stone fruit trees when dormant without any issues? I say more power to you! Stone fruit trees that are on more vigorous rootstocks will be less prone to disease and you can get away with more. Trees on semi-dwarf and dwarf rootstocks will be more sensitive to dieback, disease, and you have to take more care with timing.

In the Boise, Idaho climate one thing that I've noticed is even with waiting to prune until bloom, stone fruits have a tendency for the tissue to dry out before it completely heals over. When making cuts on 3/4 inch or thicker wood, I will use Doc Farwell's Seal and Heal to paint over the fresh cut. With using this I've had less problems with poor wound healing and with disease entering larger cuts. It's not always practical depending on the size of the tree, but I find it worthwhile to do on young trees and when making especially large cuts (2 inch thick wood or more) on mature trees

When making pruning cuts, making clean, sharp cuts is also essential to make it easier for your tree to heal the wound. I am a convert to ARS Pruners. Like many fine things made in Japan, the steel is high quality and stays very sharp. It's not clear what ARS stands for, but it would be reasonable to assume it might be "Always Really Sharp." I haven't had to sharpen my ARS tools going on 3 years now. I'm an average height man with average sized hands and I like prefer the 9 inch version. If you have hands on the smaller side, you may prefer the 8 inch ARS pruners. Last year I started using their 6 foot long reach pruners too, and while they're a little spendy, they are really nice for being able to prune lots of trees from the ground, and they make it easier to safely reach branches if you are up on a ladder for taller trees.

Stay tuned for more articles on pruning, planting, and other aspects of fruit tree care!

- Sean

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