Tree branches splitting

Question:

I'm writing to you regarding a white mulberry tree I have in front of my house. It's more than 50 years old and a few days ago I notice that the main two branches are separating (they have the shape of the letter V). They are more than 10 inches in diameter. If we cut the branch which will soon fall down, then we will have a large wound in the area where it separated. I know that sap will be dripping from the wound and that we can't stop it. What we should do?

Answer:

The recent snows have caused damage to a lot of tree branches. However, branch separation doesn't require snow; it may be the result of wind, natural poorly formed branch angles, or improper pruning. There are several options to manage the problem.

One option is to cut the branch from the tree before it separates further from the other branch. This will minimize the damage, but will leave a large wound which will be very slow to heal. The sap will flow as you described, but it will stop flowing eventually. A plant's vascular system is different from an animal's vascular system and the plant won't "bleed to death". Our vascular system is a closed loop system so loss of blood volume can be very harmful. Plants have an open vascular system. That is, they are constantly absorbing water from the soil and then transpiring it into the atmosphere. A change in the sap volume is not as catastrophic to the plant as is a change in an animal's blood volume. Besides, animal blood contains hemoglobin to carry oxygen to all the cells in an animal's body. Plants do not use sap to carry oxygen through the plant. Oxygen diffuses to the cells from the atmosphere. Don't worry about the dripping sap, it is not bleeding. This means a pruning paint may not be necessary.

You may also be able to reinforce the branch by cabling or bolting. To cable the branch you must drill a hole through the branch and insert a large eye-bolt to the branch and an opposite anchorage point on the trunk or other branch. Attach the eye-bolt with a large washer or metal plate on the side opposite the eye. Attach a strong cable to each eye-bolt and tension the cable with a turnbuckle to draw the branches back together.

Bolting is similar except that the cable and eye-bolts are replaced by a threaded rod. This threaded rod is inserted through the branch and the supporting trunk or other branch. Large washers or metal plates on the opposing sides of the branches allow nuts to draw the branches back together.

Cabling and bolting should be done by professionals who are familiar with the procedure. Look for an International Society of Arborists (ISA) certified arborist if you need to hire someone to repair or prune large branches from your trees.

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For more gardening information, visit the NMSU Extension publications World Wide Web site at https://pubs.nmsu.edu/_h/index.html

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

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