Tuesday, June 15, 2021 11:29 AM
If the recent period of extreme heat left you feeling less than enthusiastic about gardening, you’re not alone. Around here, the excitement that usually accompanies the filling of planters and windowboxes and setting transplants out into the vegetable garden was replaced with an overwhelming desire to sit on a screened porch out of the sun with a tall glass of iced tea at hand. Part of the problem was lack of preparation. In the dog days of August, we know enough to pace ourselves, and we accept that we won’t work as fast or get as much done as we would in cooler weather, but the pressure during the early days of the garden to get things into the ground and take advantage of the June warmth and sunshine drove us on.
Days of ninety-degree temperatures in early June are unusual in Maine, but these periods of extreme heat can easily become our new normal. If you look at the heat zone map, which is the companion piece to the hardiness zone map, it would suggest that we garden in Zone Three, which averages seven to 14 days above 86 degrees each year. Given the recent hot spell, we could already have used up a few of those allotted days, and it’s only June. So it behooves us to bear in mind that even in cooler coastal zones we need to be aware of the effects of elevated temperatures. For instance, if the air temperature is 90 degrees, and the relative humidity is 80%, as it was recently, your body feels like it’s 112 degrees, or as if you were suddenly transported to Joshua Tree National Park. Plus, you’re busy, you don’t have a water bottle with you, and you’re rushing around. Under these conditions it’s easy to reach 1% to 2% dehydration. That level of dehydration is very mild, almost imperceptible when it comes to feeling thirsty, but even that slight amount of dehydration negatively affects cognitive function, mood, and vigor — all needed for planting and planning. Hydrating yourself when you first start to feel the effects of dehydration is important — don’t wait until you feel thirsty to drink. If you are doing heavy work like digging or hauling around bags of garden supplements in the heat, you may need two to four glass of cool fluids per hour.
Even in northern New England it makes sense on hot days to emulate Southern gardeners and schedule strenuous activities for cooler times of the day, in the morning or late afternoon. Try to wear lightweight, light-colored, loose-fitting clothing, a wide-brimmed hat and sunscreen. Keep a damp bandana in a plastic bag in with your garden tools for face wiping, so you don’t smear dirt and insect repellent all over your face and in your eyes. If you find yourself getting too hot, or breathing heavily, head for some shade, an inside air-conditioned area, or a cooling shower, or even join the kids in an outdoor session under the sprinkler.
Extreme hot weather is even tougher on plants than it is on people. It’s easy to understand why, when you realize that while our bodies contain about 60% water, most plants are 85% to 90% water. So when we get thirsty, plants get even thirstier. Heat-loving plants like tomatoes, peppers, and eggplant, corn, melons and all kinds of squash need at least a month of 80-to-90-degree weather to develop an abundant crop. On hot days they conserve energy and moisture by slowing down, their foliage wilting during the day but perking up again in the cool of the evening. As long as they have abundant water they’ll survive, but when temperatures rise above 95 degrees for more than a day or two, most warm-weather crops will stop growing and setting fruit. The same happens to cool-weather crops at about 80 degrees. Crops like lettuce, spinach, peas, broccoli, and cauliflower suffer in hot weather. Even with an abundant and consistent supply of water, when temperatures rise over 80 degrees, these plants tend to stop growing, go to seed, or just poop out. If high temperatures persist, you can keep direct sun off foliage and lower the temperature of plants with shade covers, which can lower plant and soil temperatures by as much as 10 degrees.
Perennials that bloom in mid- and late summer, such as asters, echinacea, rudbeckia, sedum and daylilies, are usually unfazed by heat. They may need extra water when the thermometer hits 90 degrees, but the heat itself doesn’t bother them vey much. If you’re still tucking annual transplants into your gardens, choose heat-loving varieties, including zinnias and portulaca, cosmos, salvias, sunflowers (of course), celosia, the new sun-tolerant impatiens, known as SunPatiens, angelonia, also known as summer snapdragons, lantana, and petunia-like calibrachoas. Again, a good drink of water at the end of a hot day is still appreciated by these varieties, especially if they’re in planters or pots.
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