Irrigation – Thriving Yard

When people find out I have horticulture experience, they generally respond with, “I kill all my plants.” After hundreds of these interactions, I’ve discovered the number-one reason people believe they have a black thumb: Overwatering. What are the signs of overwatering plants? The signs of overwatering plants are almost identical to underwatering. Both cause wilting and dead or dying leaves. Overwatering is most common in potted plants, but it can also affect landscapes and lawns. The only way to diagnose overwatering is to check the soil. There are multiple factors that can exacerbate the problem, so it’s important to take a holistic approach to identifying and solving an overwatering issue. Why Is Too Much Water Bad For Plants? Healthy soil has a 1:1 ratio of water to air. The symptoms of overwatering are actually symptoms of a plant suffocating because they can’t breathe. Plants need oxygen and water for transpiration and photosynthesis. These processes create byproducts that must be expelled through pores in the leaves. As leaves expel excess water vapor and gasses, it creates a negative pressure in the plant’s circulatory system. This vacuum is what causes roots to pull new air and water from the soil. If the soil is waterlogged, then the roots can’t pull up oxygen. Photosynthesis and transpiration will slow down, and eventually stop if the water is unable to drain from the soil. The roots will rot from anaerobic conditions. The plant will be unable to create energy, growth will stop, and the plant will die. What Causes Overwatering Of Plants? The obvious answer is too much water. However, there are two other reasons a plant will suffer from large amounts of water: The plant is in the wrong placeThe soil is compacted clay Plants have specific requirements for sunlight, nutrition, and water. A cactus will quickly suffer from overwatering in a rainforest, while the ferns and vines thrive. If drought-tolerant plants are watered too often, they will show signs of overwatering, even in healthy soil. It’s important to become familiar with your lawn and landscape so you’re aware of the water requirements of each plant. Soil structure is the more common cause of overwatering. Even with a good irrigation schedule, compacted, clay soil will hold too much water. Clay soil textures are composed of fine particles. These particles pack tightly together and create small pore spaces. This porosity makes it hard for the soil to absorb water, but once it is saturated, it is incredibly difficult for water to drain. Plants will respond to poor drainage by growing surface-level roots in an attempt to absorb oxygen. This is especially apparent in lawns. Lawns grown in clay soil will respond to overwatering by growing a dense matt of shallow roots. When the soil is saturated, the grass will be green. However, as soon as the water drains below the first few inches of topsoil, the roots will be too shallow to access it. The grass will quickly suffer from a lack of water, and most homeowners decide to irrigate in response. This creates a cycle of shallow roots that experience extremes of moist and dry soil conditions. Potted plants and landscapes can experience the same cycle if they do not have proper drainage. Overwatered Potted Plants When potted plants die, it is almost always due to overwatering. Common signs of an overwatered potted plant are: Wilting when the soil is wetPale green or yellow foliageLeaf dropRot near the base of the plantFoul smell near the base of the plant If you have been watering a plant consistently, but it never perks up, pull it out of the pot. Roots should be white and firm. If they are yellow and mushy, the roots have rotted from overwatering. Wash the pot thoroughly with a mild bleach solution, and allow it to dry. Remove as much of the old, saturated soil as possible without damaging the roots. Pull out dead or dying roots and discard with the old soil. Make sure the pot has 3-5 drainage holes, and add some pebbles and rocks to the bottom for drainage. Have someone hold the plant in the pot while you add soil. The roots should start about 1” below the top edge of the pot. Gently tamp the plant into the soil, and place the pot up on a surface where it can drain freely. Water thoroughly, and place in indirect sunlight. Overwatered Landscapes When landscapes are overwatered, it’s usually due to poor drainage and poor placement. Common signs of overwatered landscapes are: Wilting when the soil is wetPale green or yellow foliageSoft, droopy leavesLeaf drop If only one or two plants are overwatered, while the rest look healthy, it is likely because the plant is in the wrong location. Plants that have needles, grey foliage, and hairy foliage tend to like dry conditions. Asters and succulents are also sensitive to overwatering. Try replacing the affected plants with something that tolerates more water. You can also replant the affected plants near the edges of your landscape beds. This will give them the most sunlight, and keep them away from leaky gutters. If the whole landscape looks overwatered, the problem is the soil. The first step is to examine the soil. Pull back the mulch and remove any weed barriers. If your landscape bed has a black plastic weed barrier, water will have a hard time evaporating, and it will be very difficult for organic matter and oxygen to enter the soil. Removing this black plastic will help the soil regulate water levels more efficiently. If your soil is compacted, wet, and holds shape like modeling clay, you need to add organic matter. Allow the soil to dry out until it is moist but you can’t squeeze any water from it. Next, break up the top layer of soil as much as possible without damaging established plants. Add a ½” layer of compost across the entire landscape bed, and gently rake it in. Spread a 3” layer of hardwood mulch on top to help regulate moisture and help prevent weeds. Avoid walking on your landscape bed as much as possible, because this will compact the soil and cause drainage problems. You may also want to check for leaky gutters and drain pipes that could be causing an excessive amount of water in your landscape bed. Ensure all rainwater is drained away from the house, and that you only plant water-loving plants in those areas. Overwatered Lawns Lawns are a naturally high-traffic area, and become compacted easily. Common signs of overwatering a lawn are: Pale green or yellow bladesExcessive weed growth (weeds grow faster than grass)Shallow rootsInsect damageMushrooms and ring spots (source)Spongy feel While it’s possible that you have the wrong grass for your climate, it is much more likely that an overwatered lawn is due to soil issues and watering too frequently. For lawns, it’s important to encourage deep root growth. This helps them develop some drought resistance, and enables them to handle stressful weather conditions. With compacted soil, roots grow shallow. So, to help overwatered lawns, start aerating once or twice per year, and topdressing with ½” of compost. This will incorporate oxygen into the soil, break up compaction, and add in organic matter. Click here to read the 5 step process for improving clay soil. How To Water Once you’ve diagnosed an overwatering issue, and solved any underlying placement and soil issues, it’s time to set up a healthy watering schedule. As a general rule, it is better for a plant to get too dry than too wet. Potted plants Allow the top 1/4 of potting soil to dry out before watering potted plants. Place the pot in a sink or on a well-drained surface. Water thoroughly, and wait until the water has finished running out the bottom before replacing into decorative pots or stands. Landscapes Irrigation needs for landscapes will change depending on the season, type of landscape, and age of the plants. Established shrubs and trees may not need any supplemental water. Landscapes with annuals will need significantly more water than native perennials. As a general rule, water once per week for a few hours. Pull back the mulch around plants and check the soil before watering in the spring and fall to avoid overwatering. Soil should be dry in the top inch before watering. Lawns The golden rule of lawn irrigation is deep and infrequent. Grass roots grow towards water, and for healthy lawns, we want roots to grow as deep as possible. To encourage this, water deeply, about 1”-1.5”, once per week, early in the morning. Allow the grass to show signs of water stress before watering again. This will force roots to grow down towards water held in the subsoil, as opposed to light, frequent watering, which enables roots to thrive in the top 2” of soil. After a few months of deep, infrequent watering, lawns build up a tolerance to drier conditions, and are able to utilize water more efficiently. Overwatering is the most common cause of plant death. It’s also easy to avoid if you know what signs to look for. The #1 sign of overwatering is wilting in wet soil. Fortunately, most plants can be rescued as long as you catch it early. Allow plants to wilt some before watering, and install plants with similar water needs in your landscape. For information on building a drip irrigation system or common DIY irrigation myths, please visit our irrigation articles. Related Questions How can I make my landscape more water-efficient? The best landscapes are full of native plants. Native landscapes are already adapted to the average rainfall in your area, and they will require only occasional supplemental water. Contact your local extension agency for information on native plant nurseries. Should I use sprinklers, hoses, or drip irrigation? This will depend on what you are watering. Sprinklers are the only practical way to water lawns, but they lose a lot of water to evaporation. To avoid this, water early in the morning. Landscape plants may burn or mold if the foliage is frequently damp from watering, so it’s better to install drip irrigation under a layer of mulch. You can also control how much water each plant gets. Hoses are a good way to water small areas or individual plants. For trees and shrubs, leave a hose trickling near the base of the trunk for a few hours whenever watering is required. For small gardens, watering by hand in the morning is better than attaching a sprinkler to a hose, because you can direct water to where it’s needed.