Tuesday, July 20, 2021 12:49 PM
As I write this, a true summer rain is falling. Not a blink-and-you’ll-miss-it shower or fast-moving thunderstorm, but what appears to be a rain capable of soaking fields and gardens, if it continued. But looks can be deceiving, and while we think we may not have to water the vegetable garden at the end of a day that received an hour or two of rain, according to the Maine drought monitor, our area is still experiencing moderate drought. So is it wet or dry? Should you water or wait? Sometimes it’s hard to know.
Summer storms are particularly deceptive because heavy downpours often run off more than soak in, leaving the root zone of your plants surprisingly dry. A rain gauge may tell you one thing, but a soil-moisture meter, a stick, or even a poke with a finger can indicate the true state of soil moisture. Not only do different plants have differing water needs, but different parts of your yard can have different water-holding capacities. Low-lying areas with clay-based soil may be damp for weeks after a rain, while a raised area with sandier soil is bone-dry two days later. Your grass might still be green, but that doesn’t mean your tree and shrub roots don’t need water. Frequent, shallow rains, which we seem to be having a lot of this season, may be enough to keep shallow-rooted grass green, but it’s possible your soil is dry deeper down.
Weather also makes a difference. Plants lose moisture much faster when it’s hot and dry than when it’s cooler and cloudy, and hot, dry and windy is a real killer. All of this means that you can’t go by generic advice on how much water a garden needs a week. Watering needs vary, based on such factors as the size of the plants, your soil type, and weather conditions. Your overall goal is to keep the soil damp all around and just under your plants’ roots: that might take five minutes of watering in a flower bed but 20 minutes around a young, newly planted tree.
Some people see wilted leaves as a cue for when to water, but that’s too late. Wilting means plants already are suffering drought stress and the best time to water was yesterday. Container plants are especially vulnerable to this stress. Even if you use the best potting mix, many garden containers, such as those made from terra cotta or coir hanging baskets, are very porous and notorious for drying out quickly. Metal containers can dramatically increase soil temperatures in containers, quickly drying soil and baking your plants. If you’re using containers made from these materials, you need to monitor them closely and water them more often than you would plastic or glazed ceramic containers. Larger containers hold more soil and moisture to provide roots with enough space to grow and absorb water and nutrients. The smaller the pot, the more diligent you need to be monitoring soil moisture levels. Before watering a container, be sure that the plants need water — over-watering is just as bad as under-watering. The soil surface of a container might look and feel dry to the touch, but the soil could be moist just an inch or two below the surface. To test, stick your finger into the soil as far as you can or at least to your second knuckle. If the soil feels dry at your fingertip, the plants need water. Moisture levels can change quickly on a hot, breezy summer day, so a container that feels quite moist in the morning might be dry by mid-afternoon and a late-day drink is in order. When you do need to water, do it until water runs out the bottom drainage holes. Remember, even a heavy rainstorm might not be enough to fully saturate a container’s soil from top to bottom. Plant foliage can act like an umbrella, preventing water from reaching the soil, and in containers filled with mature plants, soil might not even be visible so it’s impossible for rain to penetrate the thick growth. So keep an eye on container moisture even after a heavy rainfall.
That same umbrella effect also can mean plants under trees drying out quickly after a storm, not only because the tree canopy blocked rain, but also because big tree roots out-compete flower and shrub roots for moisture. You might have to water those plantings more than ones in a sunny, open area, which seems counter-intuitive, as they have protective shade.
Mulching your flower and vegetable beds with two to four inches of organic materials such as shredded bark, wood chips, pine straw or hay holds whatever moisture is available longer than bare soil. On the other hand, if you mulch deeply, it can take an inch or more of soaking rain just to get down to the soil surface. But you know what to do: just get that pointer finger out, test the soil and water accordingly.
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