Question: I have a very large mulberry tree that offers great shade on the west side of my house in the summer. Last spring, I hired someone to cut back the limbs over the house and carport where they were dragging on the roof and the electrical line. There is an area of branches that are thick and will be hanging over the driveway by midsummer this year. I have talked to a tree trimmer who is willing to do a minor trimming, but said that eventually I will need to cut the tree back significantly, down by about half. He said it will be healthy, leaf out, etc., and be better for the tree. He also said he would not cut it back once it begins to bud out. Does a mulberry tree this size need to be cut back by half now or in the future for its health or safety? I am thinking I may just not prune this year until I know more and am sure of what the tree needs. S. White, Doña Ana Cty.
Answer: I’m so glad you’re asking this question. I too had a huge non-fruiting mulberry in my yard when I lived in Las Cruces, and I remember wondering the same thing. At the time, we opted to trim the few branches that were touching the roof (and low enough to reach without a ladder). While our decision was largely based on having a limited budget, it turned out to be the right decision for the tree—and our precious shade.
I’m inclined to suggest waiting until the tree leafs out this spring to focus on whether or not there is any branch dieback, and then decide if the deadwood should be pruned out. Smaller dead branches within the canopy may not become a problem. If larger limbs are dead, hiring a professional tree pruner to remove them safely will be the best option. While all pruning cuts injure trees, the larger the diameter of a cut limb, the more energy is required to seal the wound.
Cutting the tree back by half sounds like a procedure known as “topping.” In addition to being detrimental to tree health, this practice has been proven to increase the chances of future limb breakage. As noted in the 2001 International Society of Arboriculture (ISA) Arborists’ Certification Study Guide, severe topping “causes branch dieback, decay, and sprout production from the cut ends, resulting in a potentially hazardous situation once the sprouts become large and heavy. Topping or heading back is not a recommended pruning practice.” If we know topping is so bad for trees, why is it still common practice? Well, there are several factors. For one, changing normalized behavior is difficult. When we see topped trees in our communities we tend to think that must be the way it should be. Also, large tree pruning is HARD. This line of work requires skill and is physically difficult—at times dangerous, and that’s why pruning services can be expensive. Selective, careful pruning also takes more time. Furthermore, many of our urban trees were topped decades ago, and corrective pruning (aka crown restoration), while possible, usually requires multiple years of successive prunings. Some tree species are more sensitive to topping than others. And an important distinction should also be made between proper care for ornamental landscape trees versus commercial tree crops. As management goals vary, so do management practices. For example, recommendations for pecan production in New Mexico include mechanical hedging of mature trees on a multi-year cycle to allow sunlight into the inner canopy to maximize yield potential (both quantity and quality). Selective, careful thinning to open the canopy of hundreds of pecan trees quickly becomes cost-prohibitive. Speaking of orchard management, NMSU Extension Fruit Specialist Dr. Shengrui Yao is hosting a virtual Fruit Grower Workshop on Wed. March 2, 2022 from 9 am to 2 pm. This is a free online event, but registration is required. Topics include orchard maintenance, irrigation, planting, and growing grapes! Visit https://rioarribaextension.nmsu.edu for more information.