The best time to water plants |

The best time to water plants

Jessica Walliser
On hot days, it's best to water before 10 a.m. Credit: Jessica Walliser

Question: My nephew and I have a $5 bet on this question. Is it safe to water your garden in full sun? He says he does it all the time; I water mine after the sun goes down because I was always told you can burn your plants. Who is right?

Neither of you are right — but not for the reasons you think. For many years, I and other “garden educators” advised folks not to water in the afternoon. It was believed that the water droplets on the foliage would behave like little magnifying glasses, magnify the sun and cause small burns on the leaf surface. However, research within the past few years has shown that such burns do not occur. However, your nephew still should not be watering in the afternoon. Here’s why:

During the hottest period of the day, much of the water your nephew is adding to his garden is lost to evaporation. It’s a very inefficient time to water. Through the remainder of the afternoon, much of the water he added is being pulled out of the soil and into the air, rather than being absorbed by the plant’s roots. When it is hot out, most plants close their stomates. These are the microscopic pores on a leaf’s surface that regulate the amount of moisture exiting the leaf. When the weather is hot, the stomates are closed and the capillary pressure within the plant is not always strong enough to pull moisture out of the soil. Even watering with a soaker hose, too much water is lost to evaporation by the end of the day.

That being said, you also should not be watering in the evening (though it’s not as bad as watering in the hot afternoon). Watering too late in the day does not allow the plants to dry before nightfall. Wet foliage promotes fungal diseases and slugs. The best time to water your garden is in the morning — preferably before 10 a.m. on hot days. Doing so prevents water stress and keeps your plants going strong.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.”

Send your gardening or landscaping questions to [email protected] or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.

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