Watering Mature Ash Trees in Arid Climates: Best Practices

Deep Watering for a 30-Year-Old Ash in Phoenix

A homeowner in Phoenix, Arizona, recently had dead branches removed from their mature ash tree and installed a soaker hose but is unsure of the correct watering schedule.

Key Principle: Deep, Infrequent Watering

Established trees need about 1 inch of water per week during the growing season, delivered slowly to penetrate 18–24 inches into the soil. This encourages deep root growth and drought resilience.

How to Measure

1. Place a shallow pan (e.g., a tuna can) under the canopy.
2. Run the sprinkler or soaker hose until the pan collects 1 inch of water.
3. Stop—this is one deep watering event.

Critical Warning for Mature Trees

Do not use a soaker hose continuously. Frequent, shallow watering draws roots to the surface, making the tree more vulnerable to heat, drought, and windthrow. Mature ash trees in desert climates often access deep groundwater and may need supplemental irrigation only during extended dry periods.

Seasonal Adjustment

• Spring/Fall: Water every 2–3 weeks if no rain.
• Summer: Weekly deep watering during extreme heat.
• Winter: Monthly if unusually dry.

Monitor tree response: Wilting, leaf scorch, or premature drop indicate under-watering; yellowing, mushrooms at base, or soggy soil suggest overwatering.