Native Tree Maintenance: To Cut or Not to Cut? A Gardener's Guide

Native Tree Maintenance: To Cut or Not to Cut?

One of the most common questions for any gardener is how best to maintain their plants. This is especially true when it comes to trees, which can live for decades and become significant features in a landscape. Decisions about pruning, trimming, and shaping can feel daunting, and it’s always a good idea to do your research. We’ll delve into the specifics of a common concern: what to do when a tree’s main trunk splits into two (or more) branches.

Understanding Codominant Stems

The scenario described by our reader, where a tree’s main trunk divides into two or more significant branches, is a common one. These are often referred to as codominant stems. While not always a problem, they can create structural weaknesses that may compromise the tree’s health and longevity. Here’s why:

• Weak Branch Unions: Where codominant stems originate from the same point, the angle of attachment is often narrow. This creates a tight ‘V’ shape. As the stems grow in diameter, the bark becomes trapped between them, forming what’s called included bark. This included bark prevents the wood from properly fusing, making the union weak and prone to splitting under stress from wind, snow, or the weight of the branches.
• Increased Risk of Failure: Trees with codominant stems are more likely to experience branch failure, which can result in significant damage to the tree itself, nearby structures, or people.
• Competition for Resources: Multiple stems originating from a single point compete for sunlight, water, and nutrients, potentially weakening the overall health of the tree.

Identifying the Problem

Carefully examine your trees to identify any instances of codominant stems. Look for:

• Multiple main branches: Where the trunk splits into two or more branches of similar size and diameter, especially at a relatively low height.
• Narrow branch angles: These angles are a key indicator of a weak union. Ideally, you want a wide ‘U’ shape, but the ‘V’ shape is a warning sign.
• Included bark: Check for bark that’s growing inward at the point where the stems meet.
• Signs of stress: such as dead or dying branches, sparse foliage, or the presence of fungal growth on the branches or trunk.

If you observe these signs, it’s worth further investigation. If you are unsure, or are dealing with a large or mature tree, consulting a certified arborist is always recommended. They can assess the structural integrity of your tree and provide expert advice on the best course of action.

What to Do: The Pruning Decision

Once you’ve identified codominant stems, the next question is whether to prune. The decision depends on several factors, including the age and size of the tree, the severity of the problem, and your own comfort level with pruning.

When to Consider Pruning:

• Young Trees: Pruning to remove or reduce codominant stems is usually best done when the tree is young. Early intervention allows the tree to develop a stronger structure from the start. The earlier the intervention, the better the chances are for the tree to heal properly.
• Trees with Weak Unions: If the branch union is visibly weak, with a narrow angle and included bark, pruning is often recommended. This can prevent a future branch failure.
• Trees in High-Risk Areas: If the tree is located near buildings, power lines, or areas with high foot traffic, pruning may be necessary to minimize potential hazards.
• Tree Health: If the tree shows signs of stress, pruning can improve air circulation and light penetration, which can help to promote overall health.

When Pruning Might Not Be Necessary:

• Mature Trees: In some cases, pruning large, mature trees with codominant stems may not be advisable, especially if the tree is already stable and appears healthy. Extensive pruning can stress the tree, and in some cases, the risk of further damage might outweigh the potential benefits.
• Small codominant stems: Sometimes there’s a small split, but the branches are very thin and not very large in comparison to the tree size. In this case, it may not be worth pruning.
• Stable Trees: If the tree appears structurally sound and isn’t in a high-risk location, you might choose to monitor it instead of pruning.

The Pruning Process

If you decide to prune, follow these guidelines:

• Timing: The best time to prune most trees is during the dormant season, typically in late winter or early spring (late February to early March in the Virginia climate). However, you can prune to remove dead, damaged, or diseased branches any time of year. If the branches are an immediate hazard, you may need to prune them immediately.
• Tools: Use sharp, clean pruning tools. This includes hand pruners for small branches, loppers for larger branches, and a pruning saw for branches too thick for loppers. Sterilize your tools between cuts and between trees to prevent the spread of disease.
• The Three-Cut Method: This method helps prevent the tearing of bark. Here’s how it works:
  1. Make a small undercut a few inches from the branch collar (the swollen area where the branch joins the trunk).
  2. Make a second cut from above, further out on the branch, to remove the weight.
  3. Make a final cut just outside the branch collar, leaving the collar intact. The branch collar contains tissues that help the tree to heal. Never cut flush against the trunk!
• Which Stem to Remove: Usually, the goal is to remove one of the codominant stems, leaving the other to become the main trunk. Select the stem to remove based on its size, angle of attachment, and overall impact on the tree’s shape. As a general rule, the larger and more dominant stem should be the one to stay. Cut it off as close to the base as possible, avoiding damage to the branch collar.
• Don’t Over-Prune: Never remove more than 25% of the tree’s canopy at once. Excessive pruning can weaken the tree and make it more susceptible to pests and diseases.

Dogwoods and Codominant Stems

Dogwoods (Cornus spp.) are beautiful and popular native trees, and they are also prone to developing codominant stems. Here’s what you should know:

• Species Susceptibility: Some dogwood species, such as the flowering dogwood (Cornus florida), are more susceptible to codominant stems than others.
• Early Intervention: If you’re planting a new dogwood, inspect it regularly and prune away any codominant stems as soon as they appear. This will help the tree to develop a strong, healthy structure.
• Mature Trees: Pruning mature dogwoods with codominant stems can be more challenging, especially if the stems are large. It’s often best to consult with a certified arborist to determine the safest course of action.
• Other Considerations: Dogwoods are relatively shallow-rooted and sensitive to changes in their environment. When pruning dogwoods, avoid removing too much foliage, as this can stress the tree. Also, consider the overall shape and balance of the tree when making pruning decisions.

Alternative Approaches and Considerations

• Cabling and Bracing: In some cases, you can use cables and braces to support weak branch unions, but this is usually best left to professionals. Cables and braces can help to prevent the branches from splitting apart, but they won’t solve the underlying structural problem.
• Monitoring: If you are hesitant to prune or unsure of the best course of action, consider monitoring the tree for a period of time. Look for signs of stress or structural problems, such as cracking, splitting, or dead branches. Have a professional arborist visit on an annual basis to assess your tree’s condition.
• Planting for the Future: When planting new trees, consider their mature size and form. Choose species that are less likely to develop codominant stems. Give trees plenty of space to grow, and avoid planting them too close to buildings or power lines.
• Consult an Arborist: For all but the simplest pruning tasks, it’s a good idea to consult a certified arborist. They can provide expert advice and services to ensure your trees are healthy and safe.

Conclusion

Dealing with codominant stems in trees is a common challenge for gardeners. By understanding the problem, identifying the signs, and following the proper pruning techniques, you can help your trees to develop strong, healthy structures that will provide beauty and shade for many years to come. Remember to consider the age and health of your tree, the potential risks, and your own comfort level when making pruning decisions, and don’t hesitate to seek professional help when needed.