Landscaping: Help trees, shrubs survive dry heat

By Gary Jones

It’s one thing to let our lawns go brown when water is tight. They probably shouldn’t have been planted in the first place. A thoughtful reimagining will no doubt result in a reasonably easy-to-achieve and beautiful substitution.

Trees and shrubs are another matter, however. They are not easily replaced, nor should we be doing so. Most well-established trees and shrubs are quite waterwise with the exceptions being some tropical plants. Removing, replanting and establishing new trees and shrubs will likely require more water than what has been uprooted.

Nevertheless, these large-scale plants won’t survive long without at least some water and a minimal bit of care.

Here’s what to consider:

1. The unusually high humidity we are having this summer is helping. While it’s hard on people, it helps plants remain hydrated, lessening the effects desiccating, hot, dry air.
2. Rather than just giving up and hoping for the best, make a plan to take care of your garden during the torrid months of August, September and October.
3. An occasional deep watering is what trees and shrubs need to survive. Start by creating a basin or “well” around the trees and shrubs that are no longer being watered automatically. It should hold 3- to 4-inches of water.
4. Unlimited hand-watering with a hose-end shutoff valve is permitted in California. Fill your “wells” two or three times from any device with a shut-off valve every three to four weeks.
5. Mulch the soil around trees and shrubs. This will help retain whatever moisture is in the soil. You will want to apply a 2- to 3-inch layer of shredded or chunked bark, oak leaves, or any organic material that is very slow to break down. Keep the mulch about 6 inches away from trunks. Mulch out to the drip line — the outward limits of the plant’s leaves.
6. Don’t feed with a high-nitrogen fertilizer. This is the opposite of normal tree and shrub feeding. Usually you want the lush, new growth that nitrogen promotes. But during a drought, you want to avoid new growth that will require additional water support. Instead, feed with a high phosphorus fertilizer that will encourage new root growth, helping plants to access more of the available water.
7. Don’t give trees or shrubs a heavy trimming until late October when the weather cools. Trimming them now will only encourage new growth, which will require more water to support them.

Most of these suggestions are excellent practices for Mediterranean climates at all times, not just during droughts. If we get normal rain during our rainy season, return to typical tree and shrub fertilizers for feeding.

—Gary Jones is Chief Horticulturist at Armstrong Garden Centers. Email your drought and gardening questions to growingdialogue@armstronggarden.com.