Though it’s not true everywhere — the forecast today for Bozeman includes a 40% chance of scattered showers — we’re fast approaching that time of the growing season when your garden, lawns and flower beds included, need to be closely monitored for moisture. How do we know when our plants aren’t getting enough water? They tell us.
Water stress is the term used to denote any moisture-related problems that plants might have. This includes too much water as well as too little. Water stress can also be caused by the quality of the water given to the plants. Water containing too many dissolved salts or grey (recycled) water that contains pollutants can also stress plants. (Phosphorus, found in many home detergents and soaps, can actually aid plant growth if proper amounts aren’t exceeded… Tip: use natural cleaning products.)
As every gardener knows, determining when plants need water is easy: their leaves wilt. But of course, you don’t want to get to this point. When you spot wilting, you’ve already stressed your plant.
How does it work? Plants draw moisture from the ground through their root and to the leaves. According to Montana State University, “The amount of force needed for a plant to remove water from the soil is known as the matric potential. When soil moisture is low, plants have to use more energy to remove water from the soil, thus the matric potential is greater. When the soil is dry and the matric potential is strong, plants show symptoms of stress. This is known as the matrix effect.” Got it?
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“Transpiration” is the process of evaporation or how plants give up moisture through their leaves and other surfaces. Almost 95% of the water a plant takes up is lost through transpiration. But that other 5% is crucial to photosynthesis and growth.
Plants have evolved to withstand drought and dry periods. How many times have we gone out to the garden at noon on a mid-summer’s day to see our leaf lettuce wilted only to return in early evening or the next morning to find it upright again? This wilting is a technique that some plants have developed to cope with hot dry conditions. It helps cut down on transpiration.
To avoid reaching the point where your plants are literally dying for water, we’ve learned to recognize the first clues. Wilting at the edges, sure; but leaves also often lose that healthy, glossy look or shine that they normally carry when they start to go through water withdrawal. Best is to use the technique we all know: stick you finger in the dirt. If you don’t come up with moisture at a depth of four inches, then it’s time to break out the watering can.
Water needs in your landscape may be less obvious. But they’re certainly observable. One of our favorite books, Gayle Weinstein’s Xeriscape Handbook: A How-to Guide To Natural, Resource-Wise Gardening suggests looking for these signs in your shrubs and trees:
- Changes in plant growth patterns over the past several years
- Continuous die-back of twigs and stems
- Yellowing of foliage especially on one side
- Unusual or early leaf and twig color
- Abnormal areas of damaged or loose bark
- Unhealthy roots–brown, dry-looking roots (can also indicate toxic chemicals in the soil)
When to water is always reason for debate. Everyone agrees that you should avoid mid-day evaporation as you water. Morning is best, some say, which gives the water time to settle into the soil. Other suggest nighttime allows for longer, less evaporation during soaking times. That’s when the arguing starts. Some gardeners feel that evening watering is a boon to insects and promotes fungal diseases. If you’d like to give your view on when to water (personally, I do it when I have time while trying to avoid times when I might be wasting water), we’d love to hear it.
One thing everyone agrees on: breaking up the soil, carefully, so as not to disturb your plant’s delicate roots, so that our precious water is better absorbed into the ground. Watering on dry hard pan? That water will run away like the gingerbread boy.
Stress from drying out will harm plants at any stage while reducing growth and harvests. Weinstein draws a distinction between acute and chronic stress. Both are to be avoided. But chronic stress, a long-term problem, is especially harmful. Acute stress happens quickly and can be just as quickly remedied. If you’re pouring water to a wilted plant and it doesn’t respond, you have exceeded acuteness. We all hate to lose plants because of oversight or carelessness.
Overwatering can be damaging as well. It result in shallow rooting which makes plants vulnerable to early drying out. It can also make plants limp and the tips of their leaves turn brown. It also invites ground-level disease, including various forms of rot. None of us would ever allow that to happen. Water is too precious to waste in this manner.
Irregular watering can also be a problem. We’ve all had ripening tomatoes split — well, at least I have — because we allowed our plant to go too long without water. Just like you, plants enjoy a degree of regularity. So don’t forget, when you’re working in the garden . . . hydrate yourself, regularly!
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