How Long After a Drenching Rain Do I Start Manually Watering?
Plants, like animals, need water to survive. Since plants manufacture their own energy from water, air and sunlight, watering garden crops and landscape plants is arguably even more important. There is no one-size-fits-all rule for when and how much to irrigate after a drenching rain. Instead, a gardener should understand the factors involved in the calculation, including soil type and climate.
Wait to water plants until the top few inches of soil have dried out.
When to Water
Many gardeners aren't certain how to determine if their plants need water. It's an important concern since veggies, flowers, trees and shrubs will die if they don't get enough water. And they may die if they get too much, as well.
But what is enough water, and what is too much? This depends on several factors, including the type of soil you have, according to the University of Arizona Cooperative Extension. Soil can be sandy, loam or clay, and each type holds different amounts of water. When there is 1 inch or less of water in a foot of sandy soil, plants growing in that soil require water or they will become stressed and eventually die. This is called the wilting point.
For loam, the wilting point is 2.2 inches of water per foot of soil, and for clay, it is 1.8 inches. While you can use a moisture meter if you like, you can learn what the soil feels like when it reaches the wilting point. For example, sandy soil that reaches the wilting point will not form a ball when squeezed.
Determining the Wilting Point
As a general rule, if the soil feels dry when you dig into it a few inches, it is time to water. If you check your garden dirt regularly, you will learn how fast it dries, which also depends on the weather. If a drenching rain is followed by foggy days, the soil is likely to stay moist for some time. If the weather turns hot and dry, the soil will dry out faster.
To make things more complicated, not all plants are the same when it comes to water requirements. Succulents, for example, are desert plants that have evolved to store water in their thick leaves and stalks. That means that they tolerate drought much better than other plants. Likewise, newly planted seedlings have not yet developed their root systems and can access moisture only in the top inches of soil. In hot weather, they need more frequent watering.
Watch for plant wilting which is another good way to time irrigation. According to the University of Florida IFAS Extension, it's okay to let your plants wilt a little, but it is essential to prevent severe water stress.
Watering Plants in Extreme Heat
Watering plants in the heat of the day – particularly on a day of extreme heat – is never a good idea since the moisture evaporates in the sun instead of getting to the roots. The best time to water plants in hot weather is early in the morning.
In fact, it's always better to water flowers, vegetables, shrubs and trees early in the morning, according to the University of Arkansas. Morning irrigation allows the water to drop down into the soil where the plant roots can access it. It also minimizes the risk of fungal diseases that are often triggered when plants spend the night with wet leaves.
Another good rule of thumb is to focus irrigation on the root area of plants. Soaker hoses help with this. And remember that it's better for your plants to give them a good soaking once or twice a week than a surface watering every day. This helps them to develop deeper roots that will make them more stable and drought-tolerant.
From Alaska to California, from France's Basque Country to Mexico's Pacific Coast, Teo Spengler has dug the soil, planted seeds and helped trees, flowers and veggies thrive. A professional writer and consummate gardener, Spengler has written about home and garden for Gardening Know How, San Francisco Chronicle, Gardening Guide and Go Banking Rates. She earned a BA from U.C. Santa Cruz, a law degree from U.C. Berkeley's Boalt Hall, and an MA and MFA from San Francisco State. She currently divides her life between San Francisco and southwestern France.