If temperatures soar into the 90s, double the amount to 2 inches per week, and add more if a heat wave persists. How to keep track? —Set a day of the week that you prefer to water—say Saturday morning—and adjust the 1-inch rule according to the week's weather you (and your plants) have just experienced.
“Just keep watering to help them hang in there until days get a little cooler,” she said. Water containers often. Soil is a plant's moisture reservoir, and since pots don't hold much soil, they dry out quickly. “In really hot weather you may need to water containers more than once a day,” Yiesla said.
But “in the heat, everyone needs more water,” Karpinos says. If you're working, exercising, or are otherwise active in hot weather, a good rule of thumb is to drink eight ounces of water every 15 to 20 minutes during the physical parts of your day, Karpinos says.
The heat of summer can be a death sentence for your plants, but over watering can as well. The best thing you can do is keep the soil moist by watering when the top 1 inch (tip of your finger) feels dry to the touch and to be aware of the symptoms listed above.
So, how hot IS too hot for plants? The general answer is around 90 degrees F, with some exceptions to the rule. This means that when temps rise above 90 and remain there for a lengthy spell: Leaves wilt.
During extremely hot weather (daytime temperatures above 90F and nighttime temperatures above 70F), try to water daily or every other day. In a 10x10-foot garden, this would mean giving your plants 8 to 9 gallons of water each day.
Plants in containers and hanging baskets may need water twice a day - especially when weather is windy and hot, containers dry out very quickly. Check often, as most will need water at least once a day, and some may need water in the morning and the evening.
Deep watering entails watering at a slow pace for long enough that the water soaks deep into the soil, where the roots are. Often this means watering for 30-60 minutes at a time, 2-3 times each week, until plants are established.
Don't Water at Mid-Day in the Sun. "Don't Water Your Plants in the Middle of the Day!" How many times have you heard that? "Only water your plants in the early mornings or late evenings." THE CHALLENGE: That's easy to say, but not always easy to do.
Watering infrequently and deeply is best. Water no more than once or twice a week. This encourages a deeper root system, which is healthier for plants, including grass. Frequent sprinklings encourage shallow roots that struggle during stressful periods of drought or harsh winters.
When working in the heat, drink 1 cup (8 ounces) of water every 15–20 minutes. This translates to ¾–1 quart (24–32 ounces) per hour. Drinking at shorter intervals is more effective than drinking large amounts infrequently. Do not drink more than 48 oz (1½ quarts) per hour!
Watering at night is not the best for your plants' leaves or overall health. Here's why. After a night time soak, leaves can stay wet for a pretty long time since they don't have the sun to dry them off. Because of this, damp leaves become extra vulnerable to fungal development.
Most plants shut down during extreme heat, so if it is over 100 degrees, it may be best to wait to water even if your plant is stressed. Throw a damp sheet over it, or mist it lightly to bring the temperature down. Mist leaves with a spray nozzle to cool down plant and reduce transpiration.
The best time to water plants is in the morning or evening.
More importantly, watering at these times actually helps the plant retain water. If you water in the afternoon, especially during summer, the heat and sun are at their peak and the plant's water will evaporate instead of absorbing into the soil and roots.
Some signs of heat related stress on plants include: leaf scorch, leaf rolling, wilting, blossom/fruit drop, sunscald, blossom end rot, and other variable conditions that could be brought on by secondary pathogens. Heat stress adversely affects plant metabolism, disrupting their vital biochemical processes.
The ideal watering schedule is once or twice per week, for about 25 to 30 minutes each time. Taking care of a lawn doesn't have to be an overwhelming, all-consuming task. Once all the tips and tricks are in your back pocket, it will be easy to come up with a routine that results in a gorgeous green lawn.
During really hot weather, water your vegetables at least two to three times a week. Watering the garden deeply is critical. The water must go down, down, down to encourage deep roots and get away from the hot soil surface.
Put the pot (with a drainage hole, of course) into a sink or basin, then fill the basin with lukewarm water until the water almost reaches the top of the pot. Let your varieties soak for about 10 minutes to an hour. You might see a few air bubbles, which are normal.
Mornings and evenings are excellent times to water gardens when using a drip irrigation system or soaker hose. Watering in the evening isn't a problem as these methods don't wet plant foliage.
Most plants grow best in temperatures ranging from 59°–86°F. When temperatures above 90°F are sustained for long periods, plant growth is slowed, and some plants begin to show signs of stress.
WATERING SCHEDULE
Deep watering helps to encourage deep root growth. Deeper roots stay cooler and stronger to better protect your lawn and garden from heat stress. Allow a deep watering at least once per week, twice if the temperature exceeds 100 degrees or more for several days in a row.
Make some shade
You can also use old bedsheets, rigged-up cheesecloth or propped-up cardboard to give your plants a break from the scorching rays, especially in the afternoon when temps reach their peak. Make sure your shade covering allows air to circulate freely around the plants.
It can take anywhere from a couple of days to a couple of months for stressed plants to recover. Recovery time depends on the amount of damage that the heat caused to the plant. If a stressed plant is completely neglected during a heatwave, it can take several months or even be impossible to revive it.