Thursday, February 11, 2016

Drought Has Culver City Resident Singing the Redwood Blues

Q. I live in the Culver City 90230.  We have a small grove of coastal redwoods, three trees about 50' tall and two saplings about 10' tall.  They evidenced considerable twig die-back, I assume in response to prolonged drought and reduced irrigation in the name of water conservation. However now all but one seem to be recovering with the help of winter rainstorms, with new foliage appearing on most branches and some stump sprouts.  Last summer we received an arborist's opinion that the trees were a lost cause and should be replaced, but now we see signs of new growth that inspire a certain optimism.  Can you give a prognosis?  If we are more generous with water, will these trees continue to recover or is this a lost cause so that we should have them removed and replaced with less thirsty trees?

A. It is normal for Redwoods to die back under drought stress and then re-foliate later once the drought is over in their native habitat, however Southern California is not their native habitat. When they recover from drought here they may not recover completely and you might have some top die-back -keep an eye out for it. Also their reaction to drought, which is to die back until conditions are better, becomes more amplified the larger the trees get. Several things can help your redwoods deal with not only drought stress, but the stress they receive being trees that are growing in an area that rarely provides their ideal conditions (foggy mornings, cool nights).

1.       Restrict traffic underneath the trees. Redwoods have shallow, sensitive roots that are damaged by human activity underneath them.
2.       Do not trim their 'skirts'. The apron of branches that occurs if you do not prune them acts as a buffer to the dry, sunny conditions that cause the soil harboring the trees' roots to dry out to rapidly and place great stress on the tree.
3.       Place a 6" layer of bark mulch under the canopy of the trees. This helps keep weeds out, and, most importantly, helps the buffer the drying out of the soil. The decomposition of the bark provides nutrients essential to the health of the redwoods.
4.       Water regularly. Although actions #2 and #3 will help keep your tree hydrated, they do need regular watering. About once a week for 20-40 minutes should be more than enough for most systems.

Also you might want to consider starting over again with the 'Aptos Blue' variety of Redwood. 'Aptos Blue' is more drought tolerant, having been collected from a grove of redwoods far inland from the central California coast. Staring over would allow you to keep the skirts on and restrict traffic underneath the trees.

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