We recommend watering your plants twice daily -- early morning and late afternoon.
Watering container plants.
Pots absorb heat, which can stress plant roots, and the soil in them dries out much faster than soil in the ground. Container plants generally need to be watered daily. During really hot weather, you may need to even water twice a day, especially smaller containers.
Usually when the first inch (2.5 cm.) or so of soil is dry, it's a good indication that watering is needed. In summer, watering outdoor potted plants is necessary daily (and even twice a day) for most species, especially when temperatures reach over 85 degrees F. (29 C.).
Watering every day is not advised. It should be done 2 to 3 times per week only to prevent a shallow root system. If possible, water during the early morning hours to ensure that the lawn dries entirely before nightfall. However, watering at any time of the day is better than not watering at all.
Plants don't need daily watering. Instead, water deeply but less frequently. Deep waterings allow the water to seep beneath the roots, which encourages the roots to grow downward.
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 your garden in summer is from 6 am to 10 am—before the heat of the day sets in, giving your plants plenty of time to drink up and any moisture on the leaves to dry off before nightfall. What is this? If watering in the morning isn't possible, the next best time is from 4 pm to 7 pm.
Stunted slow growth accompanied by yellowing leaves is also a symptom. Leaves falling off often accompanies this symptom. If your plants have yellowing leaves and old leaves, as well as new leaves that are falling at the same accelerated rate, you are overwatering.
On the other hand, watering longer but less frequently, “deep watering,” produces deep roots that mean lawns can better survive periods of drought. The ideal watering schedule is once or twice per week, for about 25 to 30 minutes each time.
Provide Slow, Deep Watering
If you are unsure how long to water new plants, aim for 30-60 seconds for small plants – longer for larger plants while moving the hose to a few locations around the plant. Avoid watering when the soil feels moist. The earth must be allowed to dry out between watering.
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.
Overwatering is one of the more common causes of plant problem. Heavy and poorly drained soils are susceptible to becoming waterlogged. Roots growing in waterlogged soil may die because they cannot absorb the oxygen needed to function normally. The longer the air is cut off, the greater the root damage.
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.
Vegetables and fruits that are developing fruit during a heat spell need regular watering to ensure good production. Vegetables typically require daily watering during summer weather, but may need a second watering when temperatures are extremely high.
Soaking the soil to a depth of 5 to 6 inches encourages plants to grow deeper roots, which in the long run will make for a healthier garden. DON'T water lightly and often, which promotes shallow root growth.
There is no hard-and-fast definition for watering deeply, but it generally means that the water can soak at least eight inches below the soil surface.
Sprinklers should be set to run for about 30 to 35 minutes at a time twice a week. Your goal is at least 1″ of water a week for your lawn. When it's hot and dry, double the water times while still trying to water just 2 or 3 days a week.
There's no cut-and-dry definition of a deep watering. Most gardeners generally refer to it as when water has soaked at least eight inches into the soil.
If a plant is overwatered, it will likely develop yellow or brown limp, droopy leaves as opposed to dry, crispy leaves (which are a sign of too little water). Wilting leaves combined with wet soil usually mean that root rot has set in and the roots can no longer absorb water.
One of the quickest, first signs of overwatering your plants is to observe occurs at the tip of the leaf. If the tip of the leaf is turning brown this is a sign of overwatering. 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.
Underwatering your plants will result in limp and wilting leaves. Your plants must have enough water to pass through the cells for turgor. If there isn't enough water, the plant will not only wilt but also close its stoma to prevent evaporation.
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.
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.
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.