Keeping Plants Healthy in Summer Heat
As the temperatures rise and the dog days of summer begin, you might find your lawn and garden looking less than their best. Some of our natural instincts - giving that dry, dead-looking lawn lots of water; feeding those droopy plants plenty of fertilizer to help them make it through - will actually kill your plants rather than save them. Read on to find some ways to prevent and repair damage from the heat of the summer sun.
The most important key to keeping plants (both your lawn and your garden) strong and resilient is to water them correctly. Deep, infrequent watering will help all types of plants develop deep roots and give them the resources they need to withstand heat and drought. Frequent, shallow watering, on the other hand, will encourage the roots to grow near the surface, making them susceptible to heat, cold and drought.
One of the worst things you can do for your lawn or garden is fertilize in the middle of a heat wave. The ingredients in fertilizers will quickly burn your susceptible plants. Even if they make it through the heat, fertilizing in mid to late summer is usually not a good idea because it can encourage growth into the fall, especially if you use fertilizers containing high amounts of nitrogen. The new growth will then be damaged by the cold fall and winter weather.
When your lawn starts to grow more slowly in the heat waves of July and August, you have two choices. You can either stop watering and allow your lawn to go dormant, or you can dedicate yourself to watering deeply about twice per week to keep your lawn alive and growing. Whatever you do, don't start giving your lawn plenty of water and then miss a watering, or allow the lawn to go dormant and then give it water to try to bring it back. Once your lawn goes dormant, you need to wait until cooler temperatures return in early September, when your lawn will spring back and start growing again.
Flower and Plant Care
Keeping your annual and perennial garden plants healthy during summer heat means using plenty of mulch and the deep, infrequent watering methods described above. Mulch will help keep moisture from evaporating out of the earth before the plant can use it. Mulch should be about two to three inches thick in most garden beds (for more on mulching, see Mulching 101). Water early in the morning before the sun becomes intense. Watering in the middle of the day can magnify the sun's rays on leaves and cause water to evaporate before it soaks down to the roots. Watering in the evening can allow the moisture to sit too long and cause disease. Early morning watering will ensure that water reaches the roots and any excess is dispersed before night.
Even with proper watering and mulching, some ailments and diseases might still occur. Bolting is one of the most common heat-related ailments in flowering plants. Bolting is when a plant flowers too soon, causing weak, dull flowers and dropped buds. Move the plant to a cooler microclimate of your yard if possible, and choose a different variety that can withstand heat better in the future.
A common problem for plants that are treated with sulfur is called sulfur phytotoxicity, where the foliage of treated plants turns black. To prevent this from occurring, stop treating plants with sulfur prior to the middle of summer. If your plants experience this issue, the only solution is to wait for them to recover. You might see less growth in these plants, but they should be otherwise unharmed.
Sunscald is essentially sunburn on a plant. It affects tomato and pepper plants that receive too much sunlight, and creates light, dry, soft spots on the fruit's exterior. This can often occur if the foliage of the plant is not doing a sufficient job of shading the fruit. Provide additional shade to the plant until the foliage bounces back, or move the plant to a shadier area.
Pruning trees and shrubs during the heat of summer can be beneficial, as long as your goal is to thin out the plant. New growth that is usually encouraged by pruning will be inhibited first by the hot, dry conditions, then by the cold of autumn and winter. However, you should never prune on the very hottest days of the summer, as this might be more than the plant (or you) can endure. Pruning can put your plant into shock, so be careful to only prune up to one fourth of the plant's foliage.
Unlike plants in the ground, potted plants should continue to receive frequent watering through the hottest, driest part of summer, especially in clay or other porous pots. Water will evaporate very quickly and needs to be replenished immediately to keep your plants from shutting down, so check them every day (or even multiple times a day). Remember that overwatering can be just as deadly as under-watering.
The key to a low-maintenance garden is choosing the right plants. If you want a beautiful garden but simply don't have the time or the desire to water your plants often, consider growing heat- and drought-tolerant perennials. Once established, these plants will come back year after year and survive and even thrive in the drought conditions often present in mid to late summer. A few examples include black-eyed Susans, butterfly weed (1), daylilies, lamb's ear, creeping phlox (2), potentilla, Russian sage (3), and snow-in-summer.