Heat hurts plants, too

KENNEWICK -- Can you believe the sweltering weather our region has been enduring?

With predictions of continued intense heat, health experts have been warning us about the dangers of this weather and telling us what precautions to take: Drink plenty of water, don't overexert yourself and try to stay indoors.

Hot weather is not only stressful to us, but it's also stressful to our garden plants. Unfortunately, there's not a lot we can do to help our plants "beat the heat" other than checking the soil and making sure it stays moist.

You may think you're applying plenty of water to your plants, but the water may not be reaching deep enough. To check, I recommend about six hours after watering that you use a trowel or shovel to check the soil for moisture.

When checking the soil moisture, consider that soil should be moist to a depth of 24 to 36 inches for trees and large shrubs, 18 to 24 inches for moderate-sized shrubs, 12 to 18 inches for small shrubs, perennials, vegetables and annual flowers. Especially during this long spell of extreme heat, you're likely to find that you need to irrigate your lawn, landscape and garden for longer periods of time and more frequently to keep the soil moist.

Here are some other ways to help your plants cope with the hot weather:

1. Apply an organic mulch to decrease the evaporation of moisture from the soil surface. An adequate layer of organic mulch can reduce evaporation from the soil by as much as 70 percent.

Organic mulches, like bark and compost, protect plant roots from damaging temperatures by reducing soil temperatures below the surface as much as 10 degrees. Rock mulches absorb heat, raising soil temperatures in the root zone. In addition, rock mulches hold and then radiate heat at night, increasing plants' water needs. Light-colored rock mulches reflect light back onto plants, also causing additional water demands on a plant.

2. On a hot, dry summer day a mature tree can use as much 100 gallons of water per hour or 2,400 gallons per day. Because trees use more water during hot weather, you should apply more water. Trees and shrubs have deeper roots than your lawn and need deep watering. Short, frequent irrigation of the lawn can not provide adequate amounts of water to your trees. It's bothersome, but you should hook up a soaker hose and use it to give your trees and shrubs a deep watering once a week during the summer.

3. When you deep-water your trees, keep in mind that the water-absorbing feeder roots of established trees are not located at the base of the trunk. Instead, they're located from the drip-line of the canopy outward, extending as much as 1 1/2 times the diameter of the canopy past the drip-line.

4. Container gardens and raised bed plantings dry out more quickly than "in-ground" plantings because of the reduced soil volume and the soil mixes. Check the soil in these situations and water when needed. You may find you'll need to water more than once a day during the hottest times of the summer.

It looks like the hot weather is going to continue, so make sure both you and your plants have enough water to drink!

* Marianne C. Ophardt is a horticulturist for the Washington State University Benton County Extension Office.