While this varies depending on weather and your local conditions, frequently usually means once or twice a day. As the plants grow bigger and become established, water less frequently but deeper. Eventually work towards watering every other day or two, giving the roots time to dry out in between waterings.
Container Plants
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.
One of the most frequently asked questions we get is how much water to use and how frequently do you water the plants. We recommend watering your plants twice daily -- early morning and late afternoon. To be more specific, early morning means 7-10am; and late afternoon means 3-5pm.
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.
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.
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.
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.
DON'T overwater.
Overwatering, however, increases the risk of root rot and fungal disease. If you see droopy stems, wilting leaves, a whitish coating (fungus), or fungus gnats in the home—pests that thrive on consistently wet soil—it's a good bet that you're watering plants too much.
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.
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 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.
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.
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.
Allowing the soil to dry out in between waterings (while not stressing the plant) is really important for preventing disease, mold, and growing stronger and healthier plants. Less frequent but deeper watering is better than frequent shallow waterings (once plants are established).
You cannot overwater with one watering. You could apply a gallon of water to the pot, and the excess would just drain out of the drainage holes. This is a waste of time and water, and can leach out nutrients, but it doesn't hurt the plant as long as the soil drains well.
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.
If, however, you apply a pint of water every day, and the soil stays constantly wet, that is over watering. This can lead to unhealthy roots or even root rot. Soil that stays constantly wet from frequent watering deprives the roots of the oxygen they need.
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.
Container plants generally need to be watered daily. During really hot weather, you may need to even water twice a day, especially smaller containers. Do the finger test to see if the potting mix feels dry two inches down.
Signs of root rot are slow growth, mushy stems, and wilting, yellow, distorted leaves (especially when the plant has been well watered, as wilting leaves can also be a sign of a dry plant).
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 heat of summer can be a death sentence for your plants, but over watering can as well. The best thing you can do is keep the soil moist by watering when the top 1 inch (tip of your finger) feels dry to the touch and to be aware of the symptoms listed above.
The notion that wet leaves on sunny days cause scorch in plants was disproved nearly ten years ago. But there is no doubt that watering in full sun is not water efficient – as much of it will evaporate before entering the soil. In the current hot breezy weather it is probably best to water in the early evening.