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.
Established Plantings
During normal summer temperatures, this type of watering can happen every 2-3 weeks. In times of extreme heat, 1-2 times each week may be necessary. Know your plants though!
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.
Both annual and perennial plants in the ground benefit from a good deep soaking up to three times a week. Allowing the water to penetrate slowly and fully into the soil (to a depth of at least 6 inches) encourages roots to grow deeper and stronger and protects them from the parched 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.
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.
Be Consistent
You should check the moisture level around the base of your plants. Determine the watering schedule you need to keep in order to maintain the right level of moisture. Watering every day or every two days doesn't matter nearly as much as consistent watering. Make a schedule and stick to it.
But don't overwater
Plants sometimes wilt from the severe sun, even when they have sufficient water. Test the soil before you water, Young said. If a pot feels heavy or the soil feels damp an inch or so under the ground, your plant probably doesn't need more moisture.
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.
Avoid full sun
In the current hot breezy weather it is probably best to water in the early evening. This gives the plants enough time to dry out, but there is still the chance for overnight water uptake by the roots. And if you want to water in the morning then start very early – before the sun is shining.
In times of extreme heat, it is vital to water your lawn for about 30 to 45 minutes daily. Once the temperatures drop below ninety, you can cut back to watering three to four times a week, until that blissful thunderstorm comes and quenches your lawn's thirst!
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. Water evaporates into the atmosphere more quickly in high heat, draining a plant's reserves.
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!
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.
In extreme heat, be sure to water the plants deep enough to keep the plants moist for as long as possible. A quick spray of your plants is not enough in extreme heat. Make sure to water deeply. Watering less often, but deeper, is far more effective than spraying the surface more often.
Use shade cloth or protective row covers.
Sensitive plants like salad greens may require a 50 – 60% shade factor, while more heat tolerant plants like squash and beans may benefit from a 30% shade cloth. A shade cloth is temporary but care should be taken to position it to block sunlight while not reducing aeration.
If your plants are in the ground (versus a pot), the general rule is that plants need one inch of water per week. However, this does NOT mean watering one time per week. That doesn't usually do the job. Plants do best when watered deeply about three times a week, factoring in the rain.
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.
Watering in the heat of the day shouldn't hurt the plants -- it actually cools them off -- but it's a far less efficient use of water as much of it will evaporate before reaching the roots.
Containers. Your containers need to be watered every day, especially when temperatures are so high. Sometimes you might even have to water in the morning and the late afternoon like we do in our Garden Center.
Signs Your Plants Are Too Hot
The leaves dry out. Excessively hot plants will dry out faster. The leaves turn yellow. One of the causes of yellow leaves is excessive heat, so this is one thing to consider!
Higher temperatures cause the plant cells which control the openings (stoma) where water is released to the atmosphere to open, whereas colder temperatures cause the openings to close. Wind & air movement: Increased movement of the air around a plant will result in a higher transpiration rate.
Containers dry out more quickly than garden beds, so it's best to increase watering in the summer. During heatwaves, water container plants twice a day, once in the morning to give plants a boost before the sun begins to bake down, and once in the evening to replenish what the day took away.
Most outdoor plants can go without water for about a week. Container plants are the thirstiest. Most need to be watered daily. If you're planning to be away, adding mulch around flower and vegetable beds helps keep moisture in longer — even if it doesn't rain during your absence.