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 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.
Newly planted trees or shrubs require more frequent watering than established trees and shrubs. They should be watered at planting time and at these intervals: 1-2 weeks after planting, water daily. 3-12 weeks after planting, water every 2 to 3 days.
As the weather heats up and plants reach full size, you may need to water containers (and especially hanging baskets) twice a day. When you water containers (or plants in the ground), check that the soil is actually dry before you 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.
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.
When plants have too little water, leaves turn brown and wilt. This also occurs when plants have too much water. The biggest difference between the two is that too little water will result in your plant's leaves feeling dry and crispy to the touch while too much water results in soft and limp leaves.
Most outdoor plants can go without water for about a week. Container plants are the thirstiest. Most need to be watered daily.
The best time to water a tree or shrub is when the top 6 to 9 inches of soil in the root zone are dry. Using a spade or hand trowel, dig a small hole under the plant canopy and feel the soil. If the soil is cool and moist 6 to 9 inches below the surface, no water is needed. If the soil is dry, it is time to water.
During the growing season, do not over-water. When you water, soak the soil approximately 12 inches deep. Wet the entire root area, which extends out to as much as three times the limb spread. Newly transplanted trees and shrubs need water more often than established ones.
The best time to water outdoor plants is in the morning when temperatures are usually cooler. This gives the plants time to absorb the water so they can get through a long, hot day. The second-best time is late in the afternoon or early in the evening. Try not to water at night.
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.
So, how hot IS too hot for plants? The general answer is around 90 degrees F, with some exceptions to the rule.
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.
Be careful not to overwater.
Water should soak in quickly; your plants should never sit in a puddle of water for an extended period of time. This can lead to root damage.
If the soil is wet, it's overwatered - if it's dry, it's underwatered. Browning edges: Another symptom that can go both ways. Determine which by feeling the leaf showing browning: if it feels crispy and light, it is underwatered. If it feels soft and limp, it is overwatered.
The first step in saving your overwatered plants is to determine how badly they have been affected. If your plants are showing some yellowing but have not yet started to wilt, you can save them by beginning to water them properly. If wilting has started to occur, you will need to work harder in order to save them.
Signs of Underwatering:
Drooping leaves that look completely lifeless can be a sign of underwatering. Soil pulling away from the outsides of the pot is another indicator that your plant may be underwatered. If you notice this happening, try shortening the length of time between waterings.
Stop Watering the Plant
But stopping your watering is always the first step. If you're overwatering, you'll likely notice that the soil is wet, so you want to make sure that soil is bone dry before you're ready to break out the watering can again.
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.
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.
When. Hands down, the best time of day to water is early in the morning. Watering during the day can increase risk of disease. If you can't water early in the morning, water late in the evening, especially before days forecasted to have dangerously high temps.