When should you water your plants — in the morning or in the evening? How much does it matter? Discover what the experts have to say about the best time of day to water your desert landscape plants.
One of the most common questions gardeners have about watering is, “What time of day should I water my plants?” The answer to this question is critical during the summer, especially during a heat wave, when every drop of water that makes it to your plants’ roots counts.
The experts agree that early morning is the best time of day to water. Here’s a look at why.
#1 Plants Take Up Water Most Efficiently in the Morning
There’s no doubt about it — mornings in the desert are cooler than the evenings. The coolest time of the day is around dawn, while the temperature peaks in the late afternoon. If you water around dusk, it will have cooled off some, but not much.
And this matters because plants take up water more efficiently when it’s cool. According to the Pima County Master Gardening program, plants dramatically reduce their water uptake when the temperature gets above 90℉.
Extreme heat interferes with a plant’s ability to take up water. Early morning watering allows the plants to take up water when they do it most efficiently.
The Arizona Department of Water Resources recommends running your irrigation between 3:00 a.m. and 8:00 a.m. It’s not only cooler then, but is usually less windy and more humid, as well. This means less water is wasted due to evaporation.
Watering midday increases
evaporation by up to 40%.
#2 Plants Need Optimal Hydration to Stay Cool
If you’ve lived in the desert for any length of time, you’re aware of how important it is to stay hydrated. Most of us never leave home without a water bottle. You would never consider going all day without drinking, figuring you’ll catch up in the evening. So why would you do that to your plants?
When day breaks, plants “wake up.” They start to photosynthesize and draw water from the soil. Water vapor is emitted through small pores on their leaves called stomata. This process is called transpiration, which, among other things, keeps plants cool.
Watering in the morning gets your plants optimally hydrated so they have enough water to transpire to keep themselves cool the rest of the day.
#3 Watering at Night Can Increase Pests & Diseases
Watering at night can increase the likelihood of pests and diseases if leaves don’t get a chance to dry off at night. This is not a big problem for landscape plants. But powdery mildew can affect some plants you might grow in the desert such as vegetable crops, penstemon, zinnias, grape vines, and roses.
#4 Mornings Are Cooler for You
No matter how much you love your plants, they are not worth risking your health over. Since mornings are cooler than evenings, watering in the morning can be the safer, more comfortable option during summer heat. Provided you can get out early enough, which is not that easy for “night owls”.
When to Water in the Evening
If some or all of your plants are hand watered and your schedule makes morning watering impractical, go ahead and water in the evening. It might not be the best time, but it is the second best time, and that’s good enough. It’s much better than watering midday or not at all. Water when it best works for you — gardening should bring you joy, not stress you out.
Also, there are a few times when you should water in the evening.
If you’ve got a plant that wilted during the day or is showing obvious signs of stress, water it as soon as you can, regardless of the time of day, provided the water you’re using isn’t too hot. If the water coming out of your spigot is too hot, you can use tap water from inside, which hopefully will be somewhat cooler.
Giving your plants a quick shower in the evening is a strategy you can use to cool stressed plants during a heat wave. If the water coming out of your hose is too hot, use the “mist” setting of your hose nozzle. The fine water droplets will cool down before hitting your plants.
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for over 15 years.
