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The Greener View: Landscape Flooding

Jeff Rugg on

Landscape Flooding

Before we go into today's topic, the effects of flooding on the landscape, we need to thank some people and count our blessings. The real heroes in our society are not the free-agent athletes making millions but the people who were out at 2 a.m. in Houston, Texas, helping those in need, whether it was their job or not. They are the ones who deserve our adoration.

Few dryland plants do well when submerged for more than a few days. Due to Hurricane Harvey, the plants in many landscapes in the Texas and Louisiana flood zones will be killed by floodwaters. A simple rule of thumb is if a plant does not normally grow on the edge of a lake or in a swamp, it will not do well being flooded. And the longer it is flooded, the worse it will do.

Floodwaters do several things to harm plants. Fast-moving water smashes down plants, and breaks or cracks their stems and branches, so they cannot straighten. This is especially true of plants without wooden stems. Perennials can be propped up for now and grow new stems next year. Shrubs and trees can be propped up until they regain their strength.

When the top of a plant is underwater, the plant has a hard time maintaining the proper level of moisture in the leaves and stems. When the waters recede, the leaves may die off. The longer the plant was underwater, the worse it will be. Mud and silt that coat the leaves will slow the plant's ability to photosynthesize, so wash off the leaves. Slow growers or already-weak plants will have a harder time recovering.

Water over the root system drowns plants slowly. For some big trees, the damage may not be apparent for several weeks, or even months. For most terrestrial plant roots to survive, the soil must have oxygen. Some plants that only grow on upland dry hill areas in nature need lots of loose soil with plenty of air. Plants as diverse as oaks and junipers are in this category. Some plants grow along stream banks and near lake shores and can take low levels of oxygen in the soil around their roots. Some maples are especially good at tolerating periodic flooding.

For most trees and shrubs, if the water is gone from the soil surface in just a few days, there should be no harm. A week or two of water over the root area will stress a plant, and it will have to be watched for other signs of problems for the next year or more. Water covering non-flood-tolerant plants for a longer time will kill them. New plants in these low areas should only be flood-tolerant.

Many parking lots are designed to hold floodwater for a while. As they release the water to the retention ponds, the water levels at the retention ponds may be kept artificially high. Trees around the edges of the ponds should be flood-tolerant, and floods will weed out dryland trees.

Most lawn grasses cannot tolerate being underwater for more than a few days without dying. Often, grasses growing in low areas are not particularly strong. Because of high humidity, they often have fungal disease problems. Many city subdivisions use park spaces and open areas as flood detention areas. These areas are not intended to stay continuously wet like a retention area; they are only supposed to hold water for several days.

The grass on a soccer field or baseball diamond will have already been weakened from the wear and tear of summer activities. If played on while the soil is wet, the ground will become compacted. These lawn areas will need lots of remedial care to come back to full strength. For the safety of the participants, a good lawn care program should be implemented before play is resumed.

People with water gardens and backyard ponds will have lost some fish and plants, as the water flooded over the ponds and caused the inhabitants to float away.

Overall, if local flooding doesn't last for more than a few days and occurs once in a while, there won't be much long-lasting effect on the landscape. Unfortunately, areas flooded longer will see many plant problems.

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Email questions to Jeff Rugg at info@greenerview.com. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

 

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