Most good gardeners are aware of, and take into account, cold-hardiness when selecting plants, but few list summer hardiness at the top of their list of plant criteria.

Most good gardeners are aware of, and take into account, cold hardiness when selecting plants, but few list summer hardiness at the top of their list of plant criteria.

In July and August the Rogue Valley can have periods where temperatures exceed 100 degrees every day. While it is difficult for people to stay cool during those periods, it can be even harder on the plants in our landscapes. Plants showing the classic signs of heat-related stress could have leaves that are burned in the center section, or have yellowed foliage despite being well-fed or be stunted and lack vigor. For plants to thrive despite our torrid summer, we must take measures to help them through the hottest days.

The most important practice to decrease the effects of heat on plants is to keep plants hydrated during hot spells. While many plants thrive in direct sun, extremely high temperatures coupled with drought will stress all but the toughest. There are no absolute rules as to the best way to water. Knowing how to irrigate your garden is becoming increasingly complicated as technology struggles to deal with shortages of supply and proper application. Think of organic mulch as nature's climate control system for your soil. It insulates against cold in the winter, retains moisture in the summer, reduces heat, reduces light reflectivity, which keeps leaves and stems cool, and will improve the soil's moisture-holding capacity and texture as it breaks down. A thick mulch of up to 4 inches in depth will provide many degrees of cooling to a plant's root zone. Limiting a plant's exposure to drying winds will also keep the effects of heat in check. A protective windbreak may be necessary to prevent the wind from pulling moisture from soil and foliage, causing drought-like conditions. Planting on the leeward side of structures will help lessen the wind's ability to complicate hot weather, as long as walls are not reflecting additional heat back on the plant. Avoid planting where reflected heat increases the effects of hot weather. The south and west sides of buildings can be brutal environments. Use care in selecting street trees whose trunks will receive the glare and added heat of pavement. Too often we see these plantings fail where better plant selection could have made all the difference in the world. When setting out new plants, prune back any unnecessary or leggy growth. The pruning should eliminate unneeded foliage in order to reduce transpiration (the loss of moisture through the leaves). Do not overdo it or you may cause leaves and stems to sunburn! Over-fertilizing shrubs and trees with nitrogen will promote fast, soft, leafy growth that is susceptible to drought and high temperatures. Spring applications of plant food are all that is necessary. Mow your lawn at the higher wheel settings as temperatures increase. The greater height actually shades the crowns of the grass plants along with the soil, and will keep your lawn cooler. Do not feed until the weather cools down and the days get shorter in late summer.

We can't stop our valley from heating up every summer, but with wise decisions and a bit of a helping hand, we can enjoy a garden that stands up to our hottest conditions.