As we clean up the fallen limbs and windswept debris from our yards left by the ‘derecho’ that stormed through here Friday night, we must be careful to drink plenty of water and try to avoid the hot sun. Better yet, do as little as possible until the heat wave passes.
This advice is good for the garden as well. Plants suffer from intense heat; that ‘wilted’ appearance gardeners are seeing today is a result of the effects of transpiration (a process similar to evaporation). Plants try to cope with intense heat by drawing up more water through the root system. This water is then released through stomata in the leaves of the plant. As the temperature rises, the rate of evaporation increases. When the soil is dry, plants can no longer absorb water and the leaves begin to ‘wilt’.
We have had at least one week now of extreme heat, and we are still seven inches below normal rainfall. Even my intrepid black-eyed Susans (rudbeckia) are curling up in protest.
Here are some garden tips I have used in combating the heat of Northern Virginia summers:
- Keep your plants mulched. Mulch will prevent water in the garden soil from drying out—think of it as sunblock for your soil. Renew the mulch in your garden beds where it has decomposed. I prefer to use leaf mold as mulch, but finely chopped wood mulch or compost will do as well. Shredded bark mulch tends to form a crust that will shed water rather than absorb it. If you use grass clippings as mulch, make sure they have dried for a few days before spreading.
- Water your plants deeply. Water deeply and infrequently rather than sprinkling every day. Clay soil needs about an inch of water per week. That’s about an hour of sprinkler time on average, but you will need to experiment with your own garden to see how long the sprinkler should run. Deep watering encourages deep roots, which will help plants to survive between watering.
- Don’t prune shrubs during hot weather. Pruning can stress a plant — and pruning in adverse weather conditions adds to the stress. If you must prune, be sure to water deeply.
- Don’t overwater the lawn. Most lawn grass in this area is “cool season grass” like fescue, bluegrass and rye grass. Those grasses like the cooler temperatures of spring and slow down or even stop growing when it gets hot. They may seem to dry up and go ‘dormant’. Just make sure your lawn receives no more than the 1 to 2 inches of water it needs per week — overwatering will make the problem worse as it produces shallow roots, making grass more vulnerable to heat or pests.
- Evaluate your garden. Take this time to look at your plants and see which plants look wilted or sunburned. Plants that look stressed may need to be moved to a less sunny spot. Don’t move them now, but plan to relocate them in the fall.
I have been studying plant recommendations from various university extension offices and botanical gardens to plan for new plant choices in case climate change continues to result in extremely hot (hotter than normal) summer temperatures. The following plants have been highly recommended: ornamental grasses, daylilies (hemerocallis), coreopsis, coneflower (echinacea), black-eyed Susan (rudbeckia), goldenrod (solidago) and succulents such as sedum.
Until the heat wave subsides, advice for gardeners and their gardens is simple: Use sunblock, water deeply and don’t work when the sun is hottest.
Hope your power is back on soon!
Eleni Silverman is a Master Gardener, Vice President of the Belle Haven GardenClub, Chair of the Landscape Committee at Thomas Jefferson High School for Science and Technology and author of the garden blog "Belle Haven Garden Maven." She admits to a fascination with all things gardening, believes even compost is engaging, and will eagerly discuss the relative merits of leaf mold versus hardwood mulch.