Heat stress in trees: signs and how to protect them
Asbury Park Tree Service · Updated
A few weeks of 90-degree days without rain is rough on trees, especially around Asbury Park, where a lot of yards sit on sandy soil that drains fast. Water you put down in the morning can be gone by afternoon.
Here’s what heat stress looks like and what you can do about it.
What heat stress is
Trees lose water through their leaves all day. It’s called transpiration, and it works a lot like sweating: the water evaporating off the leaves keeps the tree cool.
When it’s hot and dry, the tree loses water faster than its roots can pull it from the soil. That’s heat stress. A healthy tree can ride out a short hot spell. A long one, especially on a young tree or one already in rough shape, can do real damage.
Signs of heat stress
- Wilting or drooping leaves, usually the first sign. Leaves that wilt in the afternoon and perk back up overnight are a warning. Leaves that stay wilted in the morning mean the tree is in trouble.
- Brown, crispy leaf edges. This is called leaf scorch. It usually starts at the tips and edges and works inward.
- Yellowing leaves, often patchy rather than even.
- Leaves dropping early. Trees shed leaves in a drought to cut down on water loss. Some drop in August is normal. A lot is not.
- Thin or stunted new growth. The canopy looks sparse compared to last year.
Some of these look a lot like disease or insect damage. Rust-colored spots on leaves, for example, are usually a fungus, not heat. Sap oozing from the trunk can point to borers or an infection. If you’re seeing either, have someone take a look.
How to protect your trees in the heat
Water deeply, not often
A quick spray with the hose wets the surface and evaporates. What trees need is a long, slow soak that reaches the roots.
- Use a soaker hose or a hose on a slow trickle. Let it run long enough for the water to sink in deep.
- Cover the root zone. Most of a tree’s water-absorbing roots are in the top foot or so of soil, and they spread out past the edge of the canopy (the drip line). Water from a few feet off the trunk out to and beyond the drip line.
- Water once or twice a week during dry spells, rather than a little every day. Sandy soil may need it more often.
- Water in the early morning. Less evaporates, and the tree goes into the hot part of the day with full soil.
A common rule of thumb is about 10 gallons of water per inch of trunk diameter, per watering. Use it as a starting point and adjust based on your soil.
Give young trees extra attention
Trees planted in the last 2 to 3 years don’t have big root systems yet, so they dry out much faster. They need water more often in the heat. Stick a finger or a trowel a few inches into the soil near the roots. If it’s dry, water. If it’s still damp, wait. Overwatering can drown roots too.
Mulch the right way
A layer of mulch keeps the soil cooler and holds moisture in.
- Spread 2 to 4 inches of wood chips or shredded bark over the root zone, as wide as you can.
- Keep it a few inches away from the trunk. Mulch piled up against the bark (people call it a “mulch volcano”) traps moisture against the trunk and invites rot and pests.
Hold off on heavy pruning
Summer heat is a bad time for big pruning jobs. Every cut is a wound the tree has to close, and a heat-stressed tree has less energy to do it.
Removing dead, broken, or dangerous branches is fine any time. Save the larger pruning for late winter, when the tree is dormant. Learn more about tree pruning
Watch out for hot spots
Trees next to driveways, streets, parking lots, and the south or west side of a house take extra heat off the pavement and walls. Those are usually the first to show stress, so check them first and water them more.
When to call for help
Most heat-stressed trees bounce back once the weather breaks and they get some water. But call a tree company if:
- A large tree is dropping big branches or dead limbs
- Leaves stay wilted even after deep watering
- The tree didn’t leaf out properly the following spring
- You see signs of disease or insects on top of the heat damage
A tree that’s been badly weakened by drought is more likely to drop limbs in the next storm, so it’s worth having someone look at big trees near your house.
Asbury Park Tree Service handles tree pruning, tree trimming, and tree removal for homes and businesses in Asbury Park and nearby towns. Call 848-217-5320 for a free estimate.
FAQs
What causes heat stress in trees?
The tree loses water through its leaves faster than its roots can replace it. High temperatures, dry weather, wind, and fast-draining soil all make it worse.
How do I know if my tree is heat stressed?
Look for wilting leaves, brown and crispy leaf edges, patchy yellowing, early leaf drop, and thin new growth. Leaves that stay wilted overnight are the most serious sign.
When should I water trees in the summer?
Early morning is best. Water deeply once or twice a week during dry spells, rather than a little every day.
How much water does a tree need in the heat?
A common rule of thumb is about 10 gallons per inch of trunk diameter, per watering. Young trees and trees in sandy soil may need more frequent watering.
Should I prune my trees in the summer?
Only dead, broken, or dangerous branches. Save bigger pruning jobs for late winter, when the tree is dormant and under less stress.
Will a heat-stressed tree recover?
Usually, if the stress was short and the tree was healthy to begin with. Trees that go through several hot, dry summers in a row, or that were already struggling, may decline and need a professional look.