Soaking rains: too much of a good thing
By Dawn Pettinelli - UConn Home & Garden Education Center
Featured Article - posted Wed., Jun. 12, 2013
As I write this, it is raining – again! The soil in my lower vegetable and flower beds is saturated. Every footstep fills with water, so I need to wait until things dry out a bit but with more rain in the forecast, it’s hard to predict when that might be. I still have a few dozen annuals to stick into the ground, gladioli corms to put in, and the rest of my squash, zinnia and bean seeds to plant. The strawberries are beginning to rot and the slugs are starting to move in.
Plants can’t survive without water, but too much is just as bad as too little. Water is needed to hydrate the plant, to transport nutrients from the roots to the leaves, to move carbohydrates produced by photosynthesis to other parts of the plant, to regulate plant temperature, and for many other functions. Plants take in water through their roots. In this soil water, plant nutrients are dissolved, so when a plant takes up water it also takes up any nutrients present in the soil. The water moves up the stem through the xylem vessels and then into the leaves, flowers or fruits.
Plant roots also need oxygen to stay alive, and the oxygen is typically present in soils. When soils are saturated with water, the oxygen and other gases are squeezed out. Without oxygen, roots cannot take up water or nutrients, and basically the plant slowly suffocates.
Some symptoms of too much water that are now being observed include the yellowing of lower leaves, wilted plants, rotting or stunted roots, very little or no new growth, and the browning of new leaves or the tips of leaves. Tomatoes often exhibit leaves that are curled upwards when the soil becomes saturated. Usually, many of these symptoms will subside when the rains stop and the soil dries out.
Curiously, to many first-time gardeners, the symptoms of overwatering look quite similar to those of underwatering. This is because in both cases, the plants cannot take up water. In one instance, it is due to the limited availability of the liquid essence of life, and in the other, it is due to lack of oxygen which is necessary to facilitate the uptake of water.
Different species of plants require different amounts of water. With indoor plants, it is easy to control the amount of water they receive, but with outdoor garden plants, one obviously cannot control rainfall. The best a gardener can do is to provide good drainage. The texture of the soil is key to how much water can be held and stored. Soil texture refers to the relative amounts of sand, silt and clay present in the soil. Sandy loams and loamy sands would drain the fastest. Loams and silt loams hold water for longer periods of time which is great in drier conditions but problematic right now. While we gardeners can’t do much to change the texture of our soils, by at least being aware of what we have, we will have a better idea of the soil’s drainage capacities.
Soil structure, or the arrangement of soil particles, is also an important factor that determines the water drainage. Soils with good structure have plenty of pores through which water, air, plant roots and soil organisms can travel. Soil structure is enhanced by additions of organic matter and not working the soil when it is too wet. Grab a handful of soil and squeeze it. Then poke it with a finger. If it just stays in a ball with a finger imprint, it is too wet to work. If it gently crumbles, then it is friable, or of a good moisture consistency to work or cultivate. Keep in mind that compacted soils will also have reduced drainage and may prevent water from draining.
If the soil is too wet to work, try to stay out of the garden. This is especially difficult for many gardeners, like me, who still have much to do in the gardens. If you have to get things in the ground, then plan on going back when the soil dries out a bit and loosening areas that you have inadvertently compromised. Areas that are routinely moist might benefit from raised beds, permanent pathways, fall soil preparation, and/or selections of plants that tolerate poor drainage.
Seedlings and young transplants will develop symptoms of overwatering more quickly than larger, established plants because their root systems are so small. Plants grown in beds that have high amounts of organic matter (greater than 8 percent) also may become symptomatic because the organic matter acts like a giant sponge and absorbs much water. The water is held for a longer period of time and plants will look small, off-colored and stunted. The gardener may respond to this by adding fertilizer, but this would not be advisable as the plants’ root systems are already compromised and the fertilizer will not be beneficial and may actually be more detrimental.
Also, plants that are waterlogged are more susceptible to a variety of fungal organisms that cause root rots and other diseases. Lack of oxygen in the root zone causes plants to switch to anaerobic respiration. This may result in the accumulation of toxic end products like ethanol. Wet, moist areas are also the perfect habitat for slugs.
So what can a gardener do if the soils are waterlogged and plants are starting to decline? Unfortunately, for the most part we just have to wait until it dries out. You may be able to gently and lightly cultivate the top layer of soil to loosen it so that some air can get in and some drying can begin. Also there is still plenty of time to plant summer squash, beans, beets, chard, cucumbers and other vegetables, so a bountiful harvest is still in reach.
If your plants are having problems, whether due to waterlogging or other reasons, call the UConn Home & Garden Education Center (toll-free) at 877-486-6271, visit www.ladybug.uconn.edu, or get in touch with your local Cooperative Extension Center.