Q. With the temps averaging 110 F, how much and often should I be watering my shrubs and trees?
A. I would normally not increase the number of minutes on an irrigation clock but add one more watering day each week as it gets hotter. I would not recommend changing the number of minutes under normal circumstances but the number of watering days in the week. You seldom change the number of minutes on an irrigation clock after you are satisfied with your landscape irrigations.
The number of minutes on an irrigation clock delivers a set volume of water during a cycle and it does it the same every time it comes on. This set volume of water fills the same volume of soil every time for every plant on that valve or station.
This set volume of water wets the soil to the same soil depth and same spread every time it comes on. It’s like filling a gas tank on a car.
This wetted soil supplies water to plant roots. Each time after an irrigation, that specific volume of water fills the soil to the same depth and width every time. Roots grow into these areas to get the water they need. Plant roots dominate the wetted soil where there is irrigation water. They do not grow into areas where there is little to no water.
As temperatures increase, the amount of water needed by plants also increases and they consume water in the soil more quickly. Relating back to a gas tank of a car, we fill the soil with water again when the “gas tank” is about half empty. This means as temperatures get hotter we must fill the soil with water more often.
This jump from 100F to 110F (10° F change) seems big to us but it is not as big as the jump as the jump from February to June (30 to 40° F). Usually an increase of one day each week, or about 20 to 30%, is enough to handle a 10% increase F in temperature.