Here are some tips provided by The Morton Arboretum’s Plant Clinic to help trees and garden plants survive waves of heat in the 90s and above.
1. Make sure plants have enough water. Water is necessary for all of a plant’s life processes. The only way plants can cool themselves is by allowing water to evaporate through pores in their leaves. In late summer, when vegetable and perennial plants have grown full, with many leaves, they use water faster than in early summer. Water must soak into the soil for plants to absorb it.
2. Check for soil moisture. Rather than watering on a set schedule, check the garden soil for moisture. This practice is better for the plants and helps conserve water. Since plants absorb water through their underground roots, the amount of water in the soil is what matters to them. Dig down a couple of inches, and if the soil feels dry, it’s time to water. Bear in mind that soil conditions may not be the same in all parts of a yard. Water each area deeply enough so the soil feels moist 3 to 4 inches below the surface.
3. Use proper watering techniques. Trees and plants can only absorb water through their roots. It’s important to apply water relatively slowly so they have time to absorb it. Soaker hoses, which are laid on the soil surface to slowly seep water, are more efficient than sprinklers, although a sprinkler can cover a wide area. Be aware that the spray from a sprinkler can be blocked or diverted by trees, shrubs or even the large leaves of some plants such as hostas. On a hot day, much of the water from a sprinkler’s spray will evaporate rather than soaking into the soil. When watering by hand with a hose nozzle or watering wand, direct the water toward the base of the plant, rather than the leaves.
4. Certain plants need more frequent watering. Containers, vegetable gardens and newly planted perennials may need watering every couple of days or even more often in hot weather.
5. Young trees need more help accessing water. It’s especially important to provide more water for young, newly planted trees, which don’t have many roots yet. Let the hose dribble slowly into the soil, moving it around to moisten the soil around the trunk. A good dose for a young tree a few feet tall is about 10 gallons—roughly the amount resulting from a hose running at medium pressure for five minutes.
6. Mature trees need watering too. Even mature trees need watering in hot, dry weather. If the hose won’t reach, pour several buckets of water slowly into the soil around the tree.
7. Mulch. A layer of mulch over the roots of plants helps in two ways: It insulates the soil against extremes of temperature, and it prevents moisture from evaporating. Mulch can be applied at any time. Make a layer 1 to 2 inches deep on perennial beds and 3 to 4 inches around trees and shrubs. Spread the mulch out evenly, rather than piling it up against the trunk or stems. Try to keep mulch clear of the bark of a tree or shrub.
Hot weather tips courtesy of The Morton Arboretum in Lisle, Illinois. More information about how to water trees and shrubs and keep plants healthy during periods of excessive heat is available on the mortonarb.org website .
