Which trees want less water, and which are thirsty

One hose timer for the whole yard is how a coast live oak gets root rot and a young redwood crisps in August. The species already in your yard, and anything you just planted, need different amounts.

Trees that want less

Established native oaks — coast live oak and valley oak — are built for a dry summer. Deep, infrequent water in a long drought can help a mature oak. Frequent shallow watering, especially against the trunk, keeps the root crown wet and invites decay. If the oak has lived on rainfall for years, do not suddenly park a lawn sprinkler on it every other day.

Pines and many eucalyptus on South Bay lots are the same story once they are established. They will drop interior needles or leaves in a hot spell. That is not automatically a removal. Constant irrigation under a pine also favors the damp soil bark beetles like when the tree is already stressed.

Trees that want more

Redwoods in a yard are outside the fog belt they prefer. They want cool soil and a wide, slow soak, not a five-minute mist that never reaches the roots. A redwood going brown from the top in July is usually water and heat, not a mystery disease. Check soil a few inches down before you call for a takedown.

Anything planted in the last two or three years is still on establishment water, even if the species is drought-tough as an adult. A new planted tree needs a basin, mulch kept off the trunk, and a deep soak on a schedule you can actually keep. Mulch is not a substitute for water the first summers.

Fruit trees and many ornamentals near a lawn sit in the middle. They want moisture through the growing season, delivered at the dripline, not as a pond at the trunk.

A simple check

• Push a screwdriver into the soil under the canopy, away from the trunk. If it slides in and the soil is cool and dark, you are probably fine.
• If it stops in dust in July, water slowly for a long time, then wait. Sprinkling the leaves does not count.
• If the soil smells sour and the trunk flare stays wet, you are overwatering. Pull mulch back. Move emitters off the bark.

Brown leaves on one side, a fresh lean, or mushrooms at the base are a different problem than thirst. That is when photos help us tell a water issue from a tree that needs trimming or removal.

Start Easy Estimate if you want eyes on a declining tree, or call 408-439-6975.