The leaves on a couple of my trees are starting to turn brown around the edges. Should I be concerned? RW

The problem you are describing is likely an environmental condition called leaf scorch. Leaf scorch is caused by the plant’s inability to take up enough water to meet its needs during harsh summer conditions. Harsh summer conditions would exist when there were high temperatures and very little rain. Does this sound familiar? It’s a classic definition of the summer of 2022.

In leaf scorch, the edges of the leaves start to turn brown first since the edges of the leaves are farthest away from the major veins in the leaf. If the growing environment is bad enough, the entire leaf can dry out and turn brown. Consequently, trees may even begin to drop their leaves as a defense mechanism.

Susceptibility to leaf scorch can actually be exacerbated by the placement of the tree. For example, trees on the west side of the house are more exposed to the cooking afternoon sun and therefore more susceptible to leaf scorch. In addition, trees that have restricted root growth due to being up against the house or pavement like a sidewalk are also more susceptible. The tree in the photo is both, so it’s not surprising to see it suffering a bit from leaf scorch.

While the primary cause of leaf scorch is a lack of water, leaf scorch can have additional causes such as damage to roots due to construction, over-watering, over-application of fertilizer, and a loss of roots due to a dry winter or spring.

Damage to roots due to construction is a pretty obvious cause. It makes sense that if the root system was compromised, it’s not going to have a sufficient root system to meet the needs of the tree.

Over-watering is a little counter-intuitive in that we would assume in dry conditions we couldn’t apply too much water. However, water-logged soils reduce the oxygen content of the soil, and oxygen must be present to enable roots to uptake water. Too much water also inhibits root development which again limits water uptake.

Excessive fertilizer can actually burn the root system leaving it unable to draw up water. This type of damage could become evident on only a portion of the tree or the entire tree, depending on how much fertilizer and where it was applied. For the most part, trees don’t need additional fertilizer if you are fertilizing your lawn.

Lastly, leaf scorch can get set up to happen when we have a dry winter and spring. So, if we have a dry winter this year, give your trees a good soaking once a month. In mature trees, the roots can extend outward several times the height of the tree so the entire area would need to be watered.

Even though your tree might not look great right now, keep it watered and it will likely bounce back next year. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: Tom Ingram