How to care for plants after a heat wave

CORVALLIS, Ore. — When extreme heat strikes, gardens often suffer. After a heat wave, it’s common for gardeners to see signs of stress or damage — scorched leaves, drooping stems, even plant loss.

Heather Stoven, horticulturist with the Oregon State University Extension Service, says the effects of high temperatures can look dramatic, but not all damaged plants are beyond saving.

Here are recommendations from Stoven and other Extension experts for helping plants recover after a heat wave:

• Hold off on pruning. It’s fine to remove dead flowers, but avoid cutting off partially scorched leaves or doing any hard pruning. Damaged leaves can still provide shade for healthy foliage, and those with green tissue can continue photosynthesizing. Pruning too soon can encourage tender new growth that may be vulnerable to future heat — and create openings for pests and disease. If you cut back spring-blooming shrubs like rhododendrons, you may also remove buds that would bloom next year.
• Water deeply and efficiently. Use drip irrigation or soaker hoses to minimize evaporation. Overhead sprinklers lose water to the air before it reaches the roots. Water early in the morning so plants can take up moisture during the day and excess water evaporates by evening. Avoid overwatering, which can lead to root rot. To test soil moisture, insert a screwdriver into the ground; if it slides in easily, the soil is adequately moist. Be sure to water beyond the base of the plant — roots often extend well past the drip line.
• Use mulch to regulate moisture and temperature. A 2- to 3-inch layer of organic mulch helps keep soil cool, conserves moisture and protects roots.
• Wait to prune berries. While light pruning is OK, hold off on removing fruiting canes until the typical pruning time for your crop.
• Know your plants. Some plants are more tolerant of heat than others. For example, bigleaf hydrangeas (Hydrangea macrophylla) are prized for their large, colorful blooms but are less resilient in extreme heat and drought. Other species — such as panicle hydrangeas (Hydrangea paniculata) and oakleaf hydrangeas (Hydrangea quercifolia) — are better suited to sunnier, drier conditions. While not fully drought-tolerant, they may perform more reliably as climate patterns shift.

For tips on preparing your garden for future high temperatures, refer to Oregon State University Extension’s resources on gardening in extreme heat.

Previously titled How to care for heat-damaged plants