What Causes Brown Leaves on Trees?
Drought is the most common cause of leaf scorch, but there are several other reasons why leaves will turn brown early on trees. These include the opposite problem of overwatering, as well as injury to the tree’s trunk or root system, improper planting, excessive fertilization, fungal and bacterial diseases, and herbicides. Sorting out exactly what’s going on is key to finding the right solution. First, take a closer look at the affected leaves. “Depending upon species, leaf scorch symptoms come in many variations,” says Jeff Iles, Professor and Chair of the Department of Horticulture at Iowa State University. “Sometimes only the leaf margin turns brown. Sometimes the browning follows leaf veins. Sometimes it’s blotchy. And sometimes the entire leaf turns brown.” Next, take into account not only the current foliage but also the appearance of the tree over the course of the growing season. Was the leaf browning slow or sudden? For example, too much water can cause leaf scorch or dead foliage, but Iles says that browning foliage on overwatered trees comes much later in the plant’s decline. The first symptom of overwatering is a long period of yellow leaves.
How to Fix Leaf Scorch
Regardless of the cause of your tree’s brown foliage, there’s hope. “Leaf scorch is not good, but its appearance is not a reliable predictor of plant death.” Iles says. Most trees are quite resilient, so with the right care and time, they will likely rebound the following year.
Cause: Dry soil and drought.
Check the soil around your tree by using a garden trowel to dig down 18 or so inches. If the soil is dusty and crumbly, the tree is drought stressed. If your soil is difficult to dig, use a moisture meter to gauge the situation and make sure dry conditions are indeed the problem.
Solution: Water the tree.
Water the tree deeply, letting the hose or sprinkler run long enough to soak the soil to a depth of 18 to 24 inches, every 10 to 14 days. Don’t be tempted to water for short periods of time more frequently because this won’t encourage the tree to grow a deep, healthy root system. Also, keeping the soil almost constantly wet with frequent watering can invert the problem, flooding the roots to the point where they can’t get oxygen.
Cause: Overly moist soil.
When you dig down 18 inches or so and the soil is soggy, the tree could be suffering from overwatering.
Solution: Assess your watering schedule.
Irrigation systems can become too much of a good thing for trees. Turn off irrigation zones around the affected tree. Remove mulch around the tree to encourage the soil to dry faster. Check the soil again in a few days to make sure it is no longer soggy.
Cause: Limited or damaged root system.
Young or newly planted trees dry out much faster than established plants due to their developing root system. Established trees that have had their roots disturbed or cut by a lot of digging also may struggle to get enough water to all their leaves.
Solution: Time and adequate watering.
Add a layer of mulch around the tree to help conserve soil moisture. Newly planted trees often look a little rough with a few dead leaves during the first year. Making sure to give them enough water will help them come back stronger the following year.
Cause: Fungal or bacterial diseases.
Symptoms can look a lot like weather-related leaf scorch.
Solution: Call in a professional.
If you suspect your tree has a disease, an arborist or tree care company can help you diagnose and treat the problem appropriately.
Choose Native Trees
Trees that are native to your region are better adapted to the growing conditions where you live so they often can tolerate a prolonged dry spell or excessively wet spring better than non-native trees. Even if affected by leaf scorch, natives tend to bounce back easier. When you have the opportunity to add a new tree to your landscape, choose a native species.
