Soon the heat of summer will stress plants and gardens. Plants need more water when it is hot because of the process of evapotranspiration (ET).
As wind blows across leaves, or as the sun bakes them, plants pull water out of the ground via their roots. The water moves up the plant through the stems and into the leaves to keep cells hydrated. Moisture then transpires out of the plant through leaf openings called stomata. This moisture evaporates from the leaf surface and cools the plant. This process depletes soil moisture. Soil moisture is also lost as it evaporates from the soil surface with wind and sun exposure.
The drier the air around the plant, the greater the transpiration rate and the more water a plant loses. If there is not enough moisture in the soil to meet the transpiration need, the plant will wilt. It may also wilt if it cannot pull water out of the ground fast enough to meet the demand that drying winds and high temperatures create. We water to replenish soil moisture so it is available to plants.
When is the best time to water? During the heat of summer, the ideal time is to irrigate is when there is no wind, before the sun rises, or after it sets. In Carson City, water regulations (CC Municipal Code Ordinance #12.01.130) begin June 1 and continue through Sept. 30. The regulations allow irrigation 4-10 a.m. No watering is allowed 10 a.m.-6 p.m. Odd-numbered addresses water on Tuesday, Thursday, and Saturday. Even-numbered addresses water on Sunday, Wednesday, and Friday. No watering is allowed on Mondays to allow tanks to refill.
In May, lawns need, on average, 1.25 inches of water per week, depending on temperature, humidity, precipitation and wind. In June, they need about 1.5 inches per week. Although the average amount needed in July is about 1.6 inches per week, with the temperatures in the high 90s to 100s, I have often seen July lawn requirements of 2 inches per week. Lawns generally need about 1.5 inches in August and only 1.12 inches in September.
Applying more water than is recommended is wasteful and not good for the lawn. Plan to change the settings on the lawn irrigation timer each month to meet these changing evapotranspiration rates.
Trees need to be watered deeply. Water from the trunk to the dripline (tips of the branches) and soak the ground to a depth of 15 inches at each watering. Water again when the soil has dried out to a depth of 6 inches. Arrange your drip system so that emitters soak all the way around the tree. As trees mature, add more emitters farther from the trunk. And as they age, trees can go longer between waterings when watered deeply. Shrubs also need to be watered to their dripline, and depending on their size, will require less water than trees.
June 1 is less than one month away. Rather than waiting for the regulations to start, put your plants on the three-day-per-week watering cycle now. Three-day-per-week watering works very well for plant health and for the environment.
• JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension.