Tree Care Tips from Tiana, Part 2: Disease and Stress

Certified arborist Tiana George discusses the importance of evaluating your tree’s health in part two of her interview on tree care. If you missed the first part, you can find it here: Tree Care Tips from Tiana, Part 1: Planting.

Tiana George is an ISA Certified Arborist and one of the primary consultants for Tree Shepherds. With ongoing education in horticulture, she is a huge advocate of organic gardening and tree care, and believes that urban renewal is not merely good for the environment, it’s good for our minds.

Why is it important to periodically evaluate your tree’s health?

While trees are hardy organisms that can handle prolonged stress, they are especially vulnerable in urban environments. Close proximity to buildings and driveways can interfere with a tree’s water supply. The presence of concrete over root systems especially will decrease a tree’s chances to thrive. Underground pools must be built far enough away to not interfere a tree’s root zone.

And while some tree species do better in urban settings, these factors must always be kept in mind when planting a tree and when maintaining a tree’s health. In the forest, there are no buildings, no driveways, no sprinkler systems.

Are there certain tree species, which you recommend, that are better suited to urban settings?

Mexican White Oaks: These are very hardy oaks that are very pest and disease resistant.

Cedar elm: These are tall, native, easy-going trees. Their more-upright form allows for better structure and less pruning. 

Chinese Pistache: While not native to Texas, Chinese Pistache trees have adapted well here. They are insect and disease resistant, have beautiful fall color, and are fairly fast-growing. Make sure, however, to check the roots. These trees can be notorious for girdling roots, so make sure to tease the root ball when planting, plant at the correct depth, and make sure to always keep the root flare cleared and unimpeded. 

Redbud: A great native, easy-going, sun-tolerate ornamental tree which provides good shade. 

What are some species which need special considerations when grown in urban settings?

Live Oaks: Very large, sprawling trees that require a lot of space. Therefore, Live Oaks are not typically an optimal size or shape for small yards or areas close to houses or building. I recommend choosing a more upright-growing tree if you are tree shopping.

Bald Cypress: Beautiful, swamp-dwelling trees. Surface roots can put out “knees” that end in knobs and can be damaging to turf, sidewalks, and sprinkler systems. Proper watering might help encourage the trees to not develop these knees, but this is not always the case. The trees can be sensitive to drought or under-watering. Otherwise, Bald Cypress trees are very self-sufficient, not requiring much pruning. 

Maples: While beautiful trees, Maple trees are not native to Texas. For this reason, they can be a little sensitive to things like sun scald, under watering, poor soil health, etc. It is possible for the correct care for them to thrive in North Texas. However, you must be extra diligent in creating and maintaining an ideal urban landscape for them.

Red Oaks: Great trees, but can be very sensitive to herbicides (weed killers) and poor soil health. They will “talk to you” to let you know if they are stressed. For example, if your red oak leaves look pale, yellow, or “burnt,” herbicides might have been sprayed on the grass near the root system.  

Post Oaks: These are some of our favorite trees. They are the ancient beauties of the Denton county urban landscape. However, their roots are very sensitive to disturbances like construction, soil grading, improper irrigation (over-watering), and root damage and/or removal. They are very slow growing and, therefore, may take a few seasons to show symptoms to the damage.

Bradford Pears: While these trees have a beautiful, round shape and pretty white flowers in the Spring, their branching structure makes them very prone to breakage. For this reason, we caution planting these trees too close to structures or high traffic areas. Normally, they only live about 30 to 40 years. 

How quickly with a tree show signs of stress, such as extreme heat, lack of water, root problems, etc.?

Depending on the tree species, it may take days, months, or sometimes years for a tree to show symptoms of stress. Prolonged stress factors are particularly damaging to trees, so make sure to assess your urban landscape and how it may be affecting your trees. However, even if a tree is showing symptoms of stress or it is in decline, treatments or landscape modifications may be able to preserve the tree. 

What are some common signs of stress?

• The canopy as a whole not looking well. This can manifest in die back, or lack of new growth where new leaves should be coming out.
• Thinning of the canopy.
• Excessive leaf drop during, during normal times of growth.
• Mushrooms growing on the tree could also be an indication that the tree is struggling.

If a tree is showing signs of extreme stress in the summer—no leaves, bare—is there a test a homeowner can perform to tell if their tree is still alive?

Yes, it’s called the scratch test. Just take a pocket knife or your finger nail and scratch away a section of the bark on the trunk. If you can see green underneath the bark, then there is still moisture and life in the tree. If there is no green and it’s dry, then it’s unlikely that the tree is alive.

Can you explain why exposed root flares are important to a tree’s health?

The base of the tree where the trunk meets the roots is called the root flare and it is one of the most important parts of the tree. It is the intersection of the transportation of materials in the tree. It is very important for the long-term health of the tree that the flare be exposed to oxygen. Trees that are buried too deeply can develop root problems that result in fungal diseases, rotted tissues and, in some cases, girdling roots that can cut off the circulation of materials throughout the tree. I highly encourage you to expose the root flares of all of your trees, removing any weed cloths or other barriers from that area, and pruning off any small roots that are growing over or circling around the trunk and main anchoring roots. You want the root flare completely cleared and unimpeded. You may have to go pretty deep until you are able to locate the flare. In this case, you can create a little “retaining wall” around the well with rocks or bricks in order to keep materials from re-burying the tree.

Are mushrooms always an indication of decay or soil problems which might be harmful to the tree?

Not always. There are mushrooms that form on mulch. Those mushrooms are just eating away organic matter. I’d be more concerned with any mushrooms growing on woody tissue. So, if the mushrooms are on the live part of your tree, then that might be something to be concerned about. If a mushroom is on the dead part of the tree—a branch, say— then that is not a big concern. The mushroom is eating the dead part.

What about holes or wounds—cuts on the roots or to the trunk?

If it’s a big enough wound and there is some concern that the tree is structurally unsound because of the wound, then have an arborist examine it. The structural integrity of the tree is the main concern in such a situation. There is nothing that can be done to heal a cut or a wound on a tree. Don’t put spray on it or put a filler in the hole. You want to keep the wound exposed to oxygen. That’s how the tree will get the energy it needs to close the wound. If a wound is constantly wet, the tissue will rot and introduce fungal problems. Just leave wounds alone, and follow good practices in caring for and nurturing your tree: correct watering, correct soil building, etc.