Kym Pokorny
| Extension of Oregon State University

Gardeners in the northwest are disturbed by the damage their crops have suffered during the recent heat wave. Questions have come in to the Oregon State University Extension Service and experts are weighing what to do next.

There’s no denying the damage is severe, said Heather Stoven, a gardener at OSU Extension. Some plants died and others were fried from the record breaking temperatures. Even some that look extremely bad, like rhododendrons and hydrangeas, can recover. Burned leaves do not necessarily correspond to a dead plant, so patience and observation are required.

Here are some recommendations from Stoven and other experts:

Cut off dead flowers, but try to resist the urge to remove partially dead leaves, and especially don’t do a hard cut. Leaves, dead or alive, shade unburned foliage, and leaves that are still green will continue to photosynthesize. Pruning forces new growth that will be damaged in another heat event, creating a place for diseases and pests to invade the plant. Also, remember that if you prune back spring-flowering plants like rhododendrons, you are cutting off buds that will bloom next year. The foliage will grow back unless the plant is too far away.

Water deep. Use drip or soaking hoses for more efficient water use; When using an overhead sprinkler, water is lost through evaporation. The roots extend beyond the plant, so be sure to cover an area that is wider than directly under the plant. However, do not overwater. Stressed plants are more prone to pests and diseases and root rot could become a problem. To test the humidity, stick a screwdriver in the ground. It penetrates easily when the soil is damp. The best time is early morning so the plants can use the water all day when they need it and the remaining water evaporates before night.

Berries can be pruned easily, but wait until the usual cutting time to remove this year’s fruit stalks.

Apply mulch 2 to 3 inches deep. Any organic material helps maintain soil moisture and even out the temperature of the soil.

A word about hydrangeas: there are several types of hydrangeas, some of which are more heat and sun tolerant. The coveted large-leaved hydrangeas with their large blue to pink flowers are spectacular in the garden, but are less tolerant of extreme drought and heat. Other species such as panicles (Hydragea paniculata) and oak leaf hydrangeas (H. quercifolia) can be grown in the sun and can tolerate drier soils. While these plants are not considered drought tolerant plants, they may be better suited to our climate and have stunning blooms too.

About the OSU Extension Service: The Oregon State University Extension Service shares research-based knowledge with people and communities in Oregon’s 36 counties. OSU Extension addresses issues of concern to urban and rural Oregonians. OSU Extension’s partnerships and programs contribute to a healthy, prosperous, and sustainable future for Oregon.