The Q&A Archives: chilean mesquite

Question: How and when do you prune a chilean mesquite in the desert southwest?

Also, how many limbs should there be on the tree?

Answer: Desert trees are best pruned in early summer (May/early June) because they are starting their major growth period, which allows them to come back vigorously after the "shock" of pruning. As for how to prune, here are some pointers below.

To make a proper pruning cut, do not cut the branch off flush with the trunk. Cut just beyond the branch collar, a slightly raised area where the branch and trunk meet. At this point, the tree's own meristematic tissue will seal the pruning wound. It's the tree's natural healing system.

For a large heavy branch, the proper way to prune is to make three separate cuts. The first two are to eliminate the weight of the branch and prevent it from tearing bark down the trunk of the tree, which is unsightly and also allows disease/pests an entry. 1. Start with an undercut (cutting from th underside of the branch upwards) about 8-10 inches from the trunk, but cut only about half way through the branch. This prevents splitting and stripping of bark down into the trunk. 2. About 2-4 inches further past the undercut, cut the branch off (from the top to bottom). 3. Now that the weight of the heavy branch is off, make a clean, smooth cut just past the branch collar.

Don't apply any sealants to pruning cuts. Research shows that sealants will not prevent decay and actually interfere with the tree's healing ability. If we prune properly, the tree can take care of itself.

First of all, determine why you are pruning. Are branches interfering with pathways, views, etc.? One should always have a specific goal in mind when pruning. Most landscape plants are pruned far more than they require; remember, in nature, nobody is doing any pruning! If the only reason you are pruning is to reduce the size of a plant, you have the wrong plant in that space. You may want to put it something else that will grow to its full size in the space you have available.

Begin by removing any dead, broken, diseased or crossing limbs. Remove the branch at its point of origin, which means where it attaches to the main branch or trunk. Or, prune back to a bud facing in the direction that you want future growth to expand. Never leave a stub. Stubs don't heal properly. Diseases that start in the stub can spread back into the main trunk. The tree's natural healing mechanisms are located in tissue where branches join the main stem, not further out on the branch.
When cutting back to a bud, make the cut at a 45-degree angle, one-quarter inch above the desired bud, angled toward the bud. If the cut is made too close or the angle too steep, the bud may be wounded. But don?t cut too far away, leaving a stub.

Often, removing the dead, diseased, crossed or broken branches will open up the plant and no further pruning is necessary. If you determine that more is required, follow any branch back to it's point of origin and try to visualize what the plant will look like without it. Always cut back to the point of origin, never leave stubs, and don't shear or top plants, where everything is cut off at the same level. This is unhealthy for the plant and requires constant maintenance. Pruning is a maintenance task that requires skill and experience, but it gets easier over time.

If your tree is newly planted, experts say don't prune for at least 1 year. Leave low branches on the tree, as they help the trunk attain girth. Mature shade trees can add significant value to the home, soit is worth hiring a certified arborist (not just somebody who says they can prune trees, as they often have no training and destroy the tree) to make careful selections of what branches need to be cut. Also, "Desert Landscaping for Beginners," 0-9651987-3-1, Arizona Master Gardener Press, has an excellent chapter on pruning for the low desert including illustrations. I hope this info helps!

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