How Often to Water During the Heat

Q. How often should I water my trees and shrubs with all this heat. The weather got hot so quickly, I’m not sure when to water. I have a California Pepper Tree, two big palm trees and five Japanese boxwood shrubs.

California pepper tree that was planted too close to cement and so lifted it with its roots.

A. First off, don’t violate your water purveyors watering directions. These policies are in place to coordinate community water use and lower the costs of supplying water to end users like you. If you live in Las Vegas you can see it here.

            All the plants you mentioned are called “mesic” plants and require more frequent irrigation compared to (xeric) desert plants. The amount of applied water depends on the size of the plant. As plants get larger, more water is applied to a larger area (even though the water wets the same depth of soil) under the plants canopy.

Watering cacti too often can contribute to fast growth and so much succulence it cant stand up against its own weight.

            Apply water to all the area under the plants canopy. This advice might be difficult to do with larger trees like your California Pepper, so apply water to at least half the area under a plants canopy when they are big. This way they won't blow over as easily during a windstorm.

Watering frequently near the base of a plant can cause it to lose support during a windstorm.

            Lawns, annual flowerbeds and raised beds for annual vegetables require daily, or near daily, applications of water. Sometimes they need water twice a day. These plants should receive water that wets the soil to a depth of about six to 10 inches with each watering.

A piece of rebar can be used to judge how many minutes to water. Rebar pushes easily into wet soil.

            Shrubs and patio trees should be watered to a depth of 18 inches. Medium sized trees around 30 feet tall should receive enough water to wet the soil to a depth of 24 inches. Large trees need the soil wet to a depth of 36 inches after an irrigation.

            How to know if the applied water went deep enough? Use a straight, 4-foot-long steel rebar and push it into the soil after an irrigation. It stops going deeper where the water stops.

            How to water deeper with the same number of minutes? Add more drip emitters under the plant.