In the summer, tree leaves often turn brown and fall off primarily due to stress, with the three most common reasons being not enough water, too much salt, or incorrect fertilization. These issues are largely preventable and impact the tree's ability to absorb or retain water necessary for survival during hot weather.
Understanding Summer Tree Stress
Trees losing leaves in summer is a significant warning sign. Unlike deciduous trees naturally shedding leaves in the fall, summer leaf drop indicates that the tree is under stress and trying to conserve resources, typically moisture. When leaves turn brown, they are often dying tissue (sometimes called leaf scorch), which can no longer perform photosynthesis effectively.
Here are the main culprits behind this common issue:
1. Not Enough Water (Drought Stress)
This is perhaps the most frequent cause, especially during hot, dry summer periods. Trees require substantial water, particularly established ones, to keep their leaves hydrated.
- Why it happens: When the soil dries out, the roots cannot supply enough water to the leaves. The tree attempts to conserve its limited water supply by shutting down or shedding leaves. Browning often starts at the leaf edges and progresses inward.
- Signs: Wilting, curling leaves before browning; leaf edges turning crispy brown; premature leaf drop. The soil around the tree is likely dry several inches deep.
- Solutions:
- Deep Watering: Water slowly and deeply around the tree's drip line (the area directly under the outer edge of the branches), not just at the base of the trunk. Aim to moisten the soil to a depth of at least 6-12 inches.
- Frequency: Water less frequently but more thoroughly. This encourages roots to grow deeper, making the tree more drought-tolerant. Watering frequency depends on temperature, soil type, and rainfall but might be weekly or bi-weekly during dry spells.
- Mulching: Apply a 2–4 inch layer of organic mulch (like wood chips or shredded bark) around the base of the tree, keeping it a few inches away from the trunk. Mulch helps retain soil moisture and regulate soil temperature.
2. Too Much Salt
Excess salts in the soil or irrigation water can interfere with a tree's ability to absorb water, essentially causing drought stress even if water is present.
- Why it happens: High salt concentrations outside the roots draw water out of the roots or prevent water from entering them. This osmotic effect is similar to how salty soil affects plants near coastal areas or roads treated with de-icing salts. Sources can include road salt runoff, softened irrigation water, or certain fertilizers.
- Signs: Similar to drought stress – browning leaf edges (scorch), stunted growth, smaller-than-normal leaves, and premature leaf drop. Symptoms may be more severe on sides of the tree exposed to salt sources.
- Solutions:
- Flush the Soil: If feasible, heavy watering can help leach excess salts deeper into the soil profile, away from the roots.
- Improve Drainage: Good soil drainage is crucial for preventing salt buildup.
- Avoid Salt Sources: Divert runoff from salted surfaces away from trees. Be mindful of using softened water for irrigation if possible, or check salt levels. Choose appropriate fertilizers.
3. Incorrect Fertilization (Often, Too Much)
While fertilization is meant to help trees, applying too much or the wrong type can burn the roots and cause leaves to turn brown and fall off.
- Why it happens: High concentrations of fertilizer salts can damage root tissues, impairing their ability to absorb water and nutrients. This root damage leads to dehydration and browning in the leaves, similar to drought or salt stress.
- Signs: Yellowing or browning leaf tips and edges (fertilizer burn), wilting, stunted growth, and root damage (though this is harder to see). Symptoms often appear relatively quickly after application.
- Solutions:
- Soil Testing: Test your soil before applying fertilizer to understand nutrient levels and pH. This helps determine if fertilization is even necessary and what type is appropriate.
- Follow Instructions: Always follow fertilizer application rates and methods carefully. More is not always better.
- Water After Application: Watering thoroughly after applying granular fertilizer can help disperse the salts and prevent root burn.
- Avoid Over-fertilizing: Established trees in healthy soil often need minimal or no regular fertilization.
Summary of Causes & Solutions
| Cause | Why Leaves Turn Brown & Fall Off | Common Signs | Solutions |
|---|---|---|---|
| Not Enough Water | Tree conserves moisture due to lack of root uptake. | Browning edges, wilting, crispy leaves, dry soil. | Deep watering, proper frequency, mulching. |
| Too Much Salt | Salt prevents water uptake by roots. | Similar to drought (browning edges), stunted growth. | Flush soil, improve drainage, avoid salt sources, choose fertilizers wisely. |
| Incorrect Fert. | Fertilizer salts burn roots, hindering water uptake. | Brown tips/edges, wilting, stunted growth post-app. | Soil testing, follow instructions, water after, avoid over-fertilizing. |
These three most common reasons—insufficient water, excessive salt, or improper fertilization—are often at the root of tree leaf browning and dropping during the summer. Addressing these issues promptly can help your tree recover and thrive.
For more information on tree care, consider resources like Reputable Extension Service Website.
