High temperatures mean a high potential for water to evaporate before it ever reaches the roots. Avoid sprinklers and instead use spot watering at the base of the plant, soaker hoses, or drip irrigation systems to provide water efficiently. Plants in containers and hanging baskets may need water twice a day.
Take it slow. Deep soak your landscape so that moisture reaches the roots of your plants. Water slowly and deeply and watch for signs of plant heat stress. Use soaker hoses or drip irrigation if you can or hand water at the base of the plant below the leaves.
So, how hot IS too hot for plants? The general answer is around 90 degrees F, with some exceptions to the rule.
If temperatures are above 70, please water well every other day. Frequency of watering is dependent on daily temperatures: 80 degrees + - requires daily watering (slowly soak, wait, and soak again during high temp days. Morning watering is ideal, but watering in general is key.
It is so hot out there!
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.
Misting can be especially helpful on warm days when temperatures may get too high for plants and they may lose a lot of water. If you mist your plants in the morning, the water will evaporate off the surface of the leaf during the day.
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.
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.
Morning watering is actually preferable to evening watering as the plant has time to dry before the sun goes down. At night, water tends to rest in the soil, around the roots, and on the foliage, which encourages rot, fungal growth, and insects.
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.
The time needed to recover from stress is proportional to the severity of the damage. Plant heat stress recovery may take months for crops that have been ignored for too long during a heatwave; in extreme cases, it may be impossible to bring them back to life.
Avoid creating a routine of watering at the same time every day or every week. Instead, get in the habit of paying attention to the soil and the weather so you can water when the plants really need it. Containers need frequent watering.
Water on the leaves of your plants is not going to help them during hot weather. The water on the surface of a plant is the first to evaporate. You need to make sure you are getting water to the base of the plant where it can reach the root system.
Foliage will grow back unless the plant is too far gone. Water deeply. Use drip or soaker hoses for more efficient water use; water is lost to evaporation when using an overhead sprinkler. Roots extend beyond the plant, so be sure to cover an area wider than just under the plant.
Turn your hose on a slow trickle and place it 4-6” from the base of the plant. Let the hose run between 10-30 minutes, depending on the size of the root ball. Deep soaking is the best way to water your new plants. Deep soaking of a plant in its first year can be broken down into 5 phases.
In the summer and in warm climates, container plants usually require daily watering, unless they are succulents or other drought-tolerant xeriscape plants. Water deeply and slowly until water runs out of the drainage holes. Plants in hanging baskets are another step up in terms of watering needs.
If the soil surface is dry, water may puddle or run off and not be absorbed. The solution is to start slowly and gradually build up to a thorough soak. Once the top few inches are moist, the water will be absorbed more easily. Use a watering wand, drip irrigation or soaker hoses to direct water right to the root zone.
Even in a heat wave, don't overwater your plants. During the growing season, water deeply to ensure that the moisture penetrates deeply into the root growth below. Once or twice a week is enough for most plants, but it is best to check the soil for when to water.
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.
WATER BEFORE DAWN
It is often recommended that you water your lawn early in the morning, as early as 4 am and no later than 10 am. During extreme heat, watering should be done no later than 7 am.
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!
Even if the air is hot your plants will be happier without the hot sun frying them to a crisp. Plant early in the morning or at night just before or after the sun comes up. The air tends to be cooler and the sun less intense. Whatever you do, avoid the midday sun, which is the hottest and highest in the sky.
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.
When temperatures are exceptionally high and prolonged, plants can lose water through evaporation much faster than the roots can absorb it. Wilted, drooping leaves, resulting from a combination of excess water loss and high internal temperatures, are often the first signs of heat stress.