Summer yellowing usually comes from heat and drought stress, which yellows leaves and drops some early as the tree cuts its water demand, but spider mites in hot weather, iron chlorosis on new growth, and late season leaf rust can also be behind it. The pattern on the leaves and the soil moisture around the roots tell which.

Why does hot, dry weather turn leaves yellow?

Because leaves lose water faster in heat than the roots can replace it from dry soil. A stressed tree responds by yellowing and shedding leaves early, thinning its canopy to reduce water loss.

What are the usual summer causes of yellowing?

Each one leaves a different pattern:

• Heat and drought: yellowing, wilting, and early leaf drop across the canopy, often in July and August
• Spider mites: yellowing with fine pale stippling on the leaves
• Iron chlorosis: yellow new leaves with green veins, often in alkaline soil
• Leaf rust: yellowing with small reddish or yellow bumps on leaf undersides, late in the season

How is summer heat stress eased?

With deep watering, mulch, and less leaf moisture loss. Soil is watered deeply but infrequently, mulch 2 to 3 inches deep is kept off the trunk, and heavy pruning waits until the heat breaks. A clear, flexible coating that slows moisture loss from the leaves is what Wilt Pruf Plant Protector adds, diluted at 1 part concentrate to 10 parts water for summer protection.

Frequently Asked Questions

Is some summer leaf yellowing normal?

Some can be. A tree may shed a few older inner leaves during a dry spell, but yellowing that spreads or comes with wilting needs a closer look.

How can watering be stretched in a hot summer?

With a soil moisture manager. Spraying Hydretain Root Zone Moisture Manager from a hose end sprayer, rinsing it into the soil, and watering it down through the root zone reduces watering frequency for up to 3 months.

Should a yellowing tree be fertilized in summer?

Not with a high nitrogen feed. Formulas high in nitrogen in mid to late summer only push weak new growth.

Can summer yellowing come from root damage?

Yes. Roots damaged by construction, compaction, or trenching can show stress as wilting, early fall color, and leaves dropping ahead of schedule.