Hungarian researchers studied sunlit water droplets on leaves with different types of surfaces, and they found that on leaves that have "plant hairs" (think tomatoes, cucumbers, pumpkins), water droplets essentially act like magnifying glasses, intensifying damage caused by the sun—basically it's easier for the plant to get sunburned when it's wet. Plants with smooth leaves, such as maple tree leaves or ginkgo tree leaves don't suffer the same fate.
If you put in a lot of time in the garden, it's important to understand when and how to water your plants to protect your crops from burn and disease. The same goes for indoor potted plants, which not only add visual interest to your home, but also can help clean your air and reduce stress. Here's what you need to know to water correctly to keep your plants happy and hydrated.
Avoid watering your garden in the afternoon
The threat of sunburn is not the only reason to avoid watering when the sun is high—midday is never an ideal time to water plants no matter what type of leaf structure they have. "During the hottest part of the day, plants are closed up tight to retain water when in direct sun, so you waste the most water," explains gardening expert Mike McGrath. The best time to water plants is in the morning, between dawn and mid-morning, before the sun gets to be too hot. Don't water after dark, though, since the overnight moisture could promote the growth of fungus.
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Don't overdo it
Water deeply and infrequently if you can. Watering plants for several hours with a soaker hose drip irrigation system once a week beats anything else. If you don't have that kind of set up, your garden hose will do the trick—just aim it directly at the soil, close to the roots, and make sure it gets good and soaked. Try to avoid getting the leaves wet as that can lead to fungal infections.Your goal is to create soil that's damp but not soggy down to five to six inches below the surface. To figure out if your garden needs watering, simply push your finger into the soil surrounding your plants. You want the top two or three inches of the soil to be dry, with the soil below that moist. Keep aware of local weather forecasts—no need to water if rain is on the way since your plants might end up with too much water. (A tip-off that you're overwatering? Your plant's leaves start to brown at the edges and fall from the plant.)
Ditto for indoor plants
Overwatering is one of the top reasons your houseplants keep dying. Like with outdoor plants, simply check the soil moisture with your finger before watering. If it's damp, leave it alone and check back in a few days. Choosing pots with drainage holes in the bottom can also help ensure that your houseplants don't become too waterlogged. Unlike with outdoor plants, you can water your indoor plants any time of day you like, even if they're sitting on a windowsill that gets full sun The glass window filters the light so that your plants won't get sunburned. "It doesn’t really count [as direct sun]," explains McGarth. "Indoor light is a pittance of outdoor."