In hot weather you need to water in the mornings when it is cooler. This will allow more water to reach the root system before it evaporates in the heat. There may be times when you cannot schedule watering in the morning. In this case, water the plants in the late evening before bed.
And most importantly, plants absorb water more readily when they're not under heat stress—a condition that's more likely to occur when the sun is at its peak. So while it's perfectly okay to water plants while they're in full mid-day sun, it's not the most efficient way to go about it.
Watering deeply BEFORE high temperatures arrive is ideal. For most plants, watering in the morning or evening is best. Getting water on leaves will not cause burning. It can abet fungal diseases in some plants (roses, squashes), so watering most plants in the morning is ideal..
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.
In hot weather you need to water in the mornings when it is cooler. This will allow more water to reach the root system before it evaporates in the heat. There may be times when you cannot schedule watering in the morning. In this case, water the plants in the late evening before bed.
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.
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.
If the soil feels dry, it's time to water. In the spring and fall and in cooler climates, it might be sufficient to water container plants every two to three days. In the summer and in warm climates, container plants usually require daily watering, unless they are succulents or other drought-tolerant xeriscape plants.
If you forget or are too busy to water your plants on some summer mornings, you can water them at night. However, this should not be your ordinary watering time. Morning is the proper time for watering plants, though you should keep in mind that not all plants need daily watering.
When To Stop Watering Plants in Fall. When the air and soil temperatures consistently fall below 40 F, it's time to stop watering. The ground can't absorb water once the top few inches freeze. Continue to water your plants up until this point so they're as well-hydrated as possible going into winter.
Avoid watering when temperatures are below 40°F or when sustained freezing temperatures are expected within 24 hours as this water will freeze and not be available to the plants.
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.
The best time to water plants is in the morning or 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.
Check Moisture Levels
Before watering a container, be sure that the plants need water. Over-watering is just as harmful as under-watering. The soil at surface of the container might look and feel dry to the touch, but the soil might be moist just an inch or two below the surface.
If it's 70-80 degrees outside try watering 2-3 times a week. During the spring your lawn will be fairly easy to manage so you don't have to water all the time. In the blazing summer, when temperatures are between 90-100+, try watering 3-4 times a week.
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!
Mulch, mulch, and mulch some more!
Cover your soil with a blanket of organic material such as straw, leaves, shredded paper or cardboard, or bark. This will moderate soil temperature, prevent runoff and evaporation, and hold moisture in the for longer periods between waterings.
Most plants slow down their growth and production in temperatures above 90 degrees.
As a general rule, midday and evening are the worst times to water plants. The day's temperature peaks at noon, evaporating any water given to the plant before the roots are adequately soaked. In the evening, prolonged wet foliage and stems become susceptible to pathogens that can cause diseases.
During spring and summer in Southern California, she suggests drip watering three times a week for 18 minutes, then adjusting from there if the soil is too wet or dry. Don't know how to tell? Stick your finger in the soil. If it's consistently moist 2 inches down, your plants are fine.
Fall. The end of the growing season usually won't require as much watering, since temperatures start cooling and precipitation often increases. Also, most hardy plants will start slowing down their growth and losing leaves in preparation for winter, so they need less hydrating.
Browning leaves are typically caused by under watering, sunburn, or overwatering. If the leaf tips are turning brown and crunchy, the soil likely became too dry for too long in between waterings. This can also cause the plant to drop leaves.