Watering trees during the drought
You can protect your trees by giving supplemental water. Crawford says that, for most trees, 80 percent of their roots are concentrated in the top foot of soil, so make sure water penetrates the soil 6 to 12 inches deep below the tree’s canopy; irrigating more deeply than that doesn’t provide much of a benefit.
Water in the cool morning hours to minimize evaporation, using the methods below for landscape and street trees.
Note that the amount and frequency of watering varies depending on the size and species of the tree, so the following are general recommendations. Newly planted trees: These trees need 10 to 15 gallons of water two to three times a week for the first year whether there’s a drought or not. Mature landscape trees (more than 1 year old): Once a month, saturate the soil a foot deep under the canopy. It’s best to set up drip irrigation, a soaker hose or an oscillating sprinkler to run for 20 for 30 minutes. Mature street trees: Much of the root systems may be covered by concrete or other paving, so it can be hard to reach the area under the canopies. During drought, water these trees once a month using a hose at a very slow flow — so that water doesn’t run off — for 20 minutes. Or you can drill a hole in a 5gallon bucket, let it drain onto the exposed soil under the canopy, and refill enough times to give the tree 15 gallons of water. For smaller trees, you might opt to use a slow-release watering bag, such as a Treegator (www.treegator.com). Davey and other companies perform subsurface watering with a high-pressure soil probe, a tool attached to a hose that’s plunged into the soil so water reaches the root zone. This service costs about $165 for a large tree or a couple of smaller trees. While homeowners can buy soil probes to use on their own, Crawford says that residential water pressure is typically too weak to penetrate the soil in a useful way, especially if the soil is very compacted.