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Tree Care Basics: Watering

During periods without rainfall, trees should be thoroughly watered on a regular schedule. Slow, deep watering provides a cool drink for thirsty trees and creates a water reserve, much like filling up a sponge. Tree roots draw from the reserve until the next watering session. This encourages development of deeper roots and helps sustain trees during hot dry summers. A thick layer of woody mulch around your tree is also valuable to help retain soil moisture.


Current science suggests deep, soaking irrigation applied every 3-4 weeks is best. Water your trees during summer months without significant rainfall, typically June - September, adding May and October as needed. Trees For Seattle recommends that newly planted young trees need 15-20 gallons of water twice per week. Mature trees need substantially more water, potentially 1-3 hours of soaking irrigation each month, depending on tree size.


Urban landscapes often have compacted soils which makes it difficult for water to penetrate top layer of soil. A lawn sprinkler is NOT adequate and can promote shallow tree roots. Trees do not receive sufficient water from lawn irrigation systems and schedules. We suggest using a deep root watering probe that connects to your garden hose to deliver water directly to the tree’s root zone.

deep root watering maple tree
Young maple tree, planted in spring of 2021

Start 3-6 feet from the base of the trunk and push the tool 6-12 inches into the ground to get below the surface compaction layer. Turn the water on low and let it run for 15-20 minutes. Then, move the probe to a second location (1-2 big steps) within the drip line of the tree - the area between the edge of the foliage and the tree trunk. For trees up to 12 inches diameter, water in 2-4 locations around the tree. Increase the number of locations for larger trees.


You can also water your trees with just a hose. Set to low flow (just above a trickle) and thoroughly saturate the soil. It is important to run the water long and slow to avoid run-off and evaporation. Move the hose every 15-20 minutes.



Do you have questions about when and how much to water your trees? Contact the Certified Arborists at Tree133.

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