In recent summers, gardeners around the Northwest were distraught by the damage their plants suffered during heat waves.
There’s no denying damage was severe, says Heather Stoven, Oregon State University Extension horticulturist. Some plants died, and others were fried by record-breaking temperatures.
Burned leaves don’t necessarily equal a dead plant, so patience and observation are needed. Even some that look extremely bad, such as rhododendrons and hydrangeas, can bounce back.
Heather and other experts recommend the following:
Cut off dead flowers, but try to resist removing partially dead leaves. Don’t do any hard pruning. Leaves—dead or alive— will shade foliage that wasn’t burned, and those with some green remaining will continue to photosynthesize. Pruning forces new growth that will be damaged if there is another heat event, and creates a place where disease and pests can enter the plant.
Keep in mind, if you cut back springblooming plants, such as rhododendrons, you will be cutting off buds that would be flowers next year. Foliage will grow back unless the plant is too far gone.
Berries can be pruned lightly, but wait until the usual pruning time to remove this year’s fruiting canes.
Water deeply. Use drip or soaker hoses for more efficient water use; water is lost to evaporation when using an overhead sprinkler.
Roots extend beyond the plant, so be sure to cover an area wider than just under the plant. Don’t overwater, however. Stressed plants are more susceptible to pests and disease, and root rot could become a problem.
To test the moisture, stick a screwdriver in the soil. It will penetrate easily if the soil is moist. The best time is early morning so plants can use the water throughout the day when they need it. Residual water should evaporate before night.
Apply mulch 2 to 3 inches deep. Any organic matter helps retain soil moisture and evens out the temperature of the soil.
A few words about hydrangeas: There are multiple species of hydrangeas, some of which are more tolerant of heat and sun. The coveted bigleaf hydrangeas, with their large blue to pink blooms, are spectacular in the garden; however, they are going to be less tolerant of extreme drought and heat.
Other species, such as panicle (Hydrangea paniculata) and oak leaf hydrangeas (H. quercifolia), grow in sun and tolerate drier soil. While these should not be considered drought-tolerant plants, they may be better suited for our climate.