Note: Even though it’s cooler, the West is not getting much rain so below still applies.

For those of us in the West particularly, our trees need extra care during this hot time of year. In California, 100+ degrees (up into the 110s for us in SoCA) became the uncomfortable norm this past week. Luckily, we’re headed for temps in the 90s — better for giving trees the water they crave. Except for several unexpected drizzles, we’ve had no appreciable rain since April. 

Even a couple deep waterings can make the difference between a thriving tree, or a dead or diseased one.

A Review of Why? Benefits Outweigh Costs

Trees, of course, play a vital role in our community’s scenic beauty and the character of our local landscape. They also benefit the environment, helping reduce city temperatures, absorbing CO2 and cutting cooling and heating costs. (Click here for more info on benefits.)

And while rain this season locally was slightly above normal at 14-15 inches, our City of Redlands’ arborist, Erik Reeves, notes that our past droughts have caused stress to our urban forest and can result in trees becoming more vulnerable to diseases.

The cost to water a tree is small. In our city, providing adequate water to the largest of trees (approximately 160 gallons of water a month) will cost less than $1.45 a month.

Is my Tree Drought-stressed?

Signs of drought stress include:

• wilting, curling of leaves
• browning of leaf edges or dieback of twigs or branches
• leaves may be smaller or drop off
• evergreen needles may discolor
• trees become more susceptible to disease and insect damage

Supplemental water is especially important if your trees haven’t received any water since our spring rains, or if you’ve taken out lawn or reduced watering where your trees are located. 

Deep, Infrequent Watering is Best

Because of evaporation, the best time to water is early morning, or evening. These times allow the roots to absorb most of the water. 

While your tree species and soil type play roles in water needs, occasional deep watering is the most important. Too little water, such as that provided by a lawn irrigation system, can result in too shallow roots. According to a Riverside-Corona Resource Conservation District (RCRCD) publication on Waterwise Tree Care, the feeder roots that take up water on many mature trees are two to three feet deep (native trees like oaks and sycamores go considerably deeper) and are located under the leaf canopy of the tree, with some feeder roots extending beyond the canopy.  See diagram above.

There’s little chance of watering incorrectly. You can: 1) run a garden hose with a low flow of water and move it around the perimeter of the tree. Or 2) use a soaker hose. Or 3) if you have a smaller tree, water bags purchased at a garden store can be very effective. 

Remember, you want the water to soak down several feet. For a large tree, the ‘Tree Watering Guidelines’ on our City website recommends running a soaker hose with a low flow of water for 15 to 20 minutes (equivalent to four 5-gallon buckets) two times a week. 

But even less frequent will work.  During the non-rainy months, RCRCD recommends watering weekly every one to four weeks. Native trees require less, and even a deep watering monthly or several times during the dry season can greatly help a tree survive until the rains begin.

Give your trees a good soak. They will reward you with their numerous benefits in future years. 

For more info:

Southern CA Residents – Waterwise Tree Care: Help Trees Survive Drought, Tips for inland Southern California

Since I’ve written on this subject before, check this previous article for other ways to protect your trees. and below is one on native oaks.