Friday, February 18, 2011

Permaculture Pruning: Lesson Two

If you are going to cut a tree it's best to know how to do it right. Improper cutting often results in tree infection and growth of rank, poorly attached wood that become a hazard as they get larger and heavier. It also results in ugly scars that lower the beauty of the tree, no matter who you are.

If you have any questions regarding definitions please refer to Permaculture Pruning: Lesson One. I will be updating a few terms that I missed, so don't worry if you didn't catch a phrase the first time around. Permaculture Pruning: Lesson Three will talk about what your tree structure should look like.

There are three basic branches that most trees will need cut:

Side Branches: These are smaller than the branch or trunk they grow off of. Side branches should be cut just outside the collar. If you can not see the collar, go to the branch bark ridge and follow it away from the tree just to where the curve ends. Cut at a 90 degree angle through the branch at that spot. This is only an approximate placing, so please look for the collar first on every cut.

This collar is big and easy to see.

It comes out an unusual distance on the limb,
though. If if becomes a problem, I will trim it back
more in the summer.

Main Branches: When a branch has to be cut, but doesn't need to be cut all the way to the base, a heading cut is used. A heading cut cuts a limb just above a side branch. The cut should be high enough that it does not cut into the side branch or encourage it to dry out, but low enough to not leave an ugly stub. The cut should be angled so that it is slightly lower on the limb on the side that is away from the side limb. 

The size of the side branch should be at least 30% the diameter of the limb that is being cut. This gives the plant enough leaves and potential energy to keep the reaming part of the branch healthy. If the side branch is not big enough or has been trimmed too heavily, the remaining part of the branch will die or a lot of weak water sprouts will form.

I cut this one a bit too far out. No pruner is
perfect, but by trying we get better.

Co-dominant Stems: These are two branches that are about equal in size and vigor. Having co-dominant stems is like having two bosses going different directions -- neither one is in charge and neither one wants to give up power. The best solution is to take out one of the branches while it is still young.

Start the cut just above the branch bark ridge, if it is visible. If not, start as low down as you can get inside the crotch. The cut on this is always a crap shoot because co-dominant stems are rarely text book. Sometimes you have a ridge on the opposite side of the limb, just a branch width lower, sometimes you don't. If you have that secondary ridge, cut to just above it. If you don't, try to make the cut the same way you do on a heading cut.

Co-dominant stems do not have the chemical and mechanical protections that other branch connections have, so when you cut out one of the branches you should expect to see a cavity form where the cut is. The smaller and younger the limb is when you cut it, the more likely it will wound over quickly and leave a smaller cavity.

Co-dominant stems occur many places on a tree. 

There is one type of branch cutting that gets used very infrequently on trees, but is very common on shrubs: the basil cut. To make this cut you go down to where the tree meets the ground and make a clean cut. Basal cuts are a common way to renew multi-leadered shrubs like shadbush, currants, and red twigged dogwood. 

Basil cuts should only be used on trees that have multiple stems or leaders. Most often it is used to coppice the tree. If you choose to establish a coppice, remember that tree leaders are often not well attached to the roots and that you are now responsible for the safety of the tree, even if you move away or are otherwise prevented from maintaining the tree.

Many nurseries try to sell tar or other treatments to go over fresh cuts in the theory that every wound needs a bandage. Whether it is to 'keep out water' or to 'help heal the tree', the science is simply not there to prove it. 

Oftentimes simple application of known tree science refutes the bandage idea. For instance, a dressing that is intended to keep water out of a cut, ignores the fact that water for the tree is being brought up through the wood that has the cut. Simple logic says that water is more likely to be trapped by the dressing.

Permaculture Pruning: Lesson Three will start showing how to make it all come together on real plants. I look forward to seeing you there!

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