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Fresno Master Gardeners Helpline

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Helpline Hot Topic for October 2021

Tree Care During Drought

By Cynthia Zimmerman

“Love the trees until their leaves fall off, then encourage them to try again next year.” – Chad Sugg

In recent years many trees in the Fresno-Clovis area have been dying. Given our current drought conditions, it is a pretty safe bet that most trees are experiencing some stress. Leaf wilting, curling or browning of leaf edges, leaf scorch, a sparse canopy of off-color and undersized leaves, leaf yellowing and early leaf drop are all signs of drought stress. 

As homeowners it’s important to understand that during a drought trees require more care and attention than at any other time. To help your trees stay healthy and survive there are a number of steps you can take.

Water. Water is essential for healthy survival. Approximately 15-20 gallons of water should be applied by slow deep watering to at least a depth of 18 inches or more below the soil surface about once a week. Early in the morning is the optimal time. Remember that the roots go out past the drip line so be sure to water out there too.  

Test a day after watering with a soil probe, wooden dowel, or metal rod to see how far it can be easily pushed into the soil. Soil types will determine how quickly the water will be absorbed into the ground – sandy soil drains quickly from the surface while clay can cause puddling.

The best way to water is with a soaker hose or drip system. Leaves, branches, and particularly trunks should not be watered; just the roots.  A precise method of water delivery that can be used is a unique watering system called the Tree Ring Irrigation Contraption (TRIC) developed by the California Center for Urban Horticulture at UC Davis, UC Division of Agriculture and Natural Resources and Ewing Irrigation. Homeowners can put the kit together for about $100 for one large tree. For more information: https://ccuh.ucdavis.edu/tric

Avoid Pruning. Pruning a drought stressed tree can lead to problems. It not only wounds the tree which can lead to disease and insect attacks, the reserves of food stored in the branches are also removed. When a tree is already stressed it cannot restore those reserves, causing even more stress.

Go ahead and remove any branch that is broken, dead or insect-or-disease-infested and suckers at the base of the tree in order to keep the tree from being further weakened or  dangerous. Otherwise do minimal pruning; instead of the usual rule of removing 1/3, remove no more than ¼ of a trees mass, and only if necessary.

Avoid Fertilizing. Fertilization promotes tree growth which increases its need for water. If you feel you absolutely must fertilize, avoid quick-release fertilizer, never fertilize when it is hot, and do not use fertilizer with nitrogen greater than 10%.

Remove Competition. Plants compete for water, nutrients, light, and space. If turf is underneath a tree, more water will be needed because turf absorbs the greater part of the water applied to the surface. If possible, remove the turf.

Apply organic mulch in a circle around the tree base, 3-4 inches thick and at least 3 feet out. Leave a clear 6-8 inch circle at the base of the trunk in order to avoid rot. Avoid using rock as mulch since it absorbs heat and can stress the roots.

For information about specific trees:

Trees for small spaces              https://ucanr.edu/sites/mgfresno/files/42114.pdf

Ultra small trees for small spaces              https://ucanr.edu/sites/mgfresno/files/42258.pdf

Shopper’s Guide for Deciduous Trees              https://ucanr.edu/sites/mgfresno/files/174791.pdf

Shopper’s Guide for Evergreen Trees              https://ucanr.edu/sites/mgfresno/files/174792.pdf

Need a tree professional?  To find a local certified arborist go to the ISA website: https://www.isa-arbor.com/For-the-Public

For more information about drought and trees:  

FAQs for Helping Your Trees Survive during a  Drought  https://ucanr.edu/blogs/MBMG/blogfiles/20400.pdf

Pruning Drought Stressed Shade Trees  https://sacmg.ucanr.edu/files/183437.pdf

Drought Care for Trees  https://ccmg.ucanr.edu/files/219422.pdf

Trees Come First During a Drought  https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=46513