How Often to Water Walnut Trees

Water a young walnut tree every 7–10 days depending on heat and rain – every 3–5 days in very hot weather – giving about 15–20 litres (4–5 gallons) each time. Water needs rise with age: a tree over 8 years old may need 80–160 litres (20–40 gallons) every 5 days in summer. The most critical period is kernel fill in mid to late summer; a tree that runs short of water then produces nuts that look normal but contain small, dark kernels. In cold regions, reduce and stop watering in late summer so shoots harden off before winter.

How Much Water Do Walnut Trees Need?

The idea that walnuts are deep-rooted and need no water applies to old village trees left to themselves. A productive orchard needs irrigation. A cropping walnut needs around 1,100–1,350 mm (43–53 in) of water a year, rainfall included. In many regions rainfall supplies less than half of that, and most of it falls outside summer.

How much a tree needs depends on its age and canopy size, the summer heat, the soil's water-holding capacity, and whether the ground is mulched or covered.

Watering a Young Walnut Tree

• At planting: 30–50 litres (8–13 gallons).
• Regular watering: 15–20 litres (4–5 gallons) every 7–10 days; every 3–5 days in very hot weather. University of California guidance for home trees is up to 3–5 gallons (11–19 litres) a week for young trees.
• Soil type: sandy soils may need water every 3–5 days; heavy soils every 1.5–2 weeks.
• Check the soil: if the top 15–20 cm (6–8 in) is dry in hot weather, water again.
• Do not water little and often – daily sprinkling keeps roots shallow and weak.

Watering Mature Trees

Start irrigating mature trees after flowering. Water deeply and infrequently so the soil is wetted 1–2 m (3–6 ft) down: with flood or soaker methods, every 2–3 weeks for 12–24 hours; with drip, more continuously. Water around and beyond the drip line, where the feeding roots are, not against the trunk.

The Critical Period: Kernel Fill

A walnut first completes its shell and size, then fills the kernel. Nut growth and kernel fill fall in early to late summer (June to August in the Northern Hemisphere). Never let the tree go dry during these months. Water needs are lower in late spring and rise as kernel filling speeds up.

A tree short of water during kernel fill usually keeps its nuts but cannot fill them:

• kernels do not fill the shell and leave gaps;
• kernels shrivel;
• kernels darken and stain;
• exposed nuts suffer sunburn on the husk, darkening the kernel beneath.

Because the shell is already formed, these nuts look normal until cracked.

Drip Irrigation and Micro-Sprinklers

Drip, micro-sprinkler or subsurface drip systems suit walnuts better than flood irrigation:

• Water reaches the feeding roots under the canopy evenly, with less waste.
• Leaves and nuts stay dry, reducing anthracnose and walnut blight.
• Fewer weeds grow.
• Fertilizer can be applied through the water.

A single ring of drippers around a young tree is enough at first; widen the system as the canopy grows.

Too Much Water Is Also Harmful

• Roots starve of oxygen and fine roots rot.
• Water pooling around the trunk invites crown rot (Phytophthora).
• Waterlogged, heavy soils increase iron deficiency (yellow leaves).
• Watering young trees every 1–2 days slows their growth.

Keep water away from the trunk and lower branches of established trees, and avoid prolonged saturation.

When to Stop Watering

• Cold regions: reduce and stop watering large trees from late summer, young trees by mid-autumn. Late watering keeps shoots growing; they enter winter soft and are damaged by early frost, which reduces next year's crop.
• Mild regions: cropping trees need the most water in late summer; stop about two weeks before harvest so husks split cleanly, then give a final watering after harvest.

Common Watering Mistakes

• Leaving the orchard to rainfall in the belief that walnuts need no water.
• Skipping irrigation during kernel fill in mid to late summer.
• Watering young trees a little every day.
• Keeping drippers right against the trunk and not moving them out as the tree grows.
• Watering into autumn in cold regions.
• Wetting leaves and trunks with flood or overhead irrigation.

Related Walnut Guides

• How to grow walnut trees: complete guide
• Walnut tree fertilizer
• Why is my walnut tree dropping nuts?
• Walnut tree yield and years to bear

Frequently Asked Questions

How often should I water a newly planted walnut tree?

About every 7–10 days, 15–20 litres (4–5 gallons) each time; every 3–5 days in hot weather. Avoid daily light watering.

How much water does a mature walnut tree need?

A cropping walnut needs around 1,100–1,350 mm (43–53 in) of water a year including rain; in summer a large tree may use 80–160 litres (20–40 gallons) every few days.

Are walnut trees drought tolerant?

Established trees survive drought, but they do not crop well without water – drought during kernel fill leaves kernels small and dark.

When should you stop watering walnut trees?

In cold regions, reduce watering from late summer so shoots harden off. In mild regions, stop about two weeks before harvest and water again afterwards.

What are signs of overwatering a walnut tree?

Yellowing leaves, wilting despite wet soil, slow growth and dark, soft bark at the soil line (a sign of crown rot).