Sudden Leaf Drop in Local Trees

Last week, we reported on the burn damage to leaves of local trees and plants caused by the excessive heat.  Descano Gardens’ forest of Camelias was heavily damaged by the heat, according to the Pasadena Star News:

“The temperature reached 115 degrees at Descanso Gardens Friday, a record. Staff at Descanso are still tallying the damage, but an early estimate is that about 70 percent of the gardens’ roughly 10,000 camellia plants have sunburn,”

Now we are starting to see another form of damage, “sudden leaf drop,”  where a significant percentage of leaves are suddenly dropping from local trees.

The phenomenon is particularly bad among our California Sycamore street trees which have also been plagued by infestations of the polyphagous shot hole borer beetle.

But local experts say we may be able to help our trees by deep watering them  to get them through this stress period of extra heat.  You can also add mulch at the base of the tree. Also, don’t remove the leaf litter that falls to the ground because mulch and leaf litter will help preserve the moisture the trees desperately need.

“Mulch is vital!” advised arborist Nick Mook. “One of the most important things that can be done for our local landscape is to instruct gardeners not to blow away leaf litter or mulch. Let that stay on the soil around the base of a tree so it will hold the moisture.”

Mook also recommends deep and frequent irrigation for trees that are stressed.  He says watering in the morning is best,  but if you are deep watering it can be done any time of day. Watering with spray heads in the evening is generally a bad idea because it can promote the growth of fungus and mold. Watering during the heat of the day should be avoided because it’s wasteful as much of the water evaporates.

The best way to water trees is with soaker hoses wrapped around the tree at the drip line and left on for several hours. After a session with the soaker hose, wait one day then test the soil again to make sure the water penetrated to 12-16.”  

For trees in your yard, if you have emitter sprinklers, you can add more time to station that serves the tree.

Garden Designer Judy Horton recommends the following best practices for gardening for you trees:

• Check with a soil probe during times of drought, if the soil is bone dry, irrigate with a soaker hose to the depth of at least 16” during the tree’s growing season.
• The root crown (base of trunk) is a vulnerable area. Never leave dirt, debris or mulch piled against the trunk and do not allow water to collect on or near the root crown.
• Do not till soil or plant anything other than ground cover under the drip line.
• Keep lawn and groundcover well away from the trunk.
• Tree roots are in the top 12-24” of soil and extend well beyond the drip line (the outermost area of the tree canopy (foliage).