OSU Linn County Master Gardener.
Are some of your plants still looking fried from the recent heat wave?
OSU Extension Ask An Expert service (https://extension.oregonstate.edu/ask-expert) is answering high numbers of inquiries about how to save stressed plants. Some of their knowledgeable staff have written helpful articles we can access for free at the above website (drop down ask-expert then search for “plant heat”).
Here are some high points from the horticulture specialists:
Most plants grow best between 60 and 90 degrees. Extreme air and soil temperatures (hot and cold) slow down growth in plants. To protect themselves plants may roll or cup their leaves, wilt, dry edges of leaves to save the centers, drop blossoms or fruit, flower (bolt) early, or get scald spots where overexposed to the sun.
Some plants have dried, some have partially fried. They may come back to normal with some care, cooler temperatures and moisture, but with fewer good leaves.
Some root systems may be in a slowed semi-dormant state waiting for better conditions.
If we keep the crispy leaves for now they can provide shade for undamaged leaves. If the burned leaves are removed, the new growth may suffer from sun damage as hot days continue.
Pruning some plants may even remove next year’s flower buds. It is recommended to cut off only dead flowers and wait to see if the plant can recover on its own. Pruning only during the normal time for fruits and berries will be the best way to avoid further weakness that can invite disease or dehydration.
Mature trees show heat stress by dropping needles or leaves some time after the heat event. It’s a mess, but they are self-healing as well as they can.
Scorched plants should be watered deeply to hydrate the roots at 6″ or more. Adding a couple of inches of organic mulch may help insulate the soil and provide better water-holding capacity. Water the soil in the morning so plants can suck up the moisture into the stems and leaves as needed during the day. Keep the soil evenly moist if possible. Drip and soaker hose systems are efficient during hot summer months. If the plants are wilted they need water as soon as possible because they aren’t getting enough to sustain their strength. Light overhead watering in late afternoon with a mist nozzle can ease plant stress but saturating leaves in warm weather can encourage some diseases to develop.
Weeding in the morning can remove competition for water and nutrients in the soil. Planting, transplanting, pruning, fertilizing or treating with chemicals at temperatures over 80 degrees will increase stress in plants that are trying to heal or put on new growth.
Providing shade with shadecloth, old sheets, old screens, lattice or almost anything will help plants tolerate hot, dry days. Move planted containers out of the sun to keep them from cooking.
It’s time to start fall/winter cool season crops but they may refuse to germinate in hot weather. They can be started indoors, like early spring sowing. Providing shade for a few days when transplanted outside will increase their chance of survival.
Soaking seeds overnight before planting and planting a little deeper than recommended on the packet in late summer may help germination. Newly planted seeds may need to be watered morning and evening to keep the soil evenly moist until they grow good root systems.
If it is evident some plants will need to be replaced, get lists of drought-tolerant plants, shrubs and trees at
http://extension.oregonstate.edu/droughttolerance.
Diane Hyde
OSU Linn County Master Gardener
