Flooded gardens and wet soil can cause even more problems than a drought. Unless our plants are in moveable containers, there is little we can do except wait for the weather to change. After that, it is time to take stock of how your garden held up.
Effects of Flooding
If your soil is waterlogged, chances are good your plants are showing signs of stress or soon will be, because flooded soils contain insufficient amounts of oxygen. This means that plant roots cannot take up and release water or release excess carbon dioxide, which they must do to survive. Plants may paradoxically look like they are wilting, but it is not because of too little water, it is because they can no longer access the available water. This leads to root rot and death.
A short-term period of soggy soil probably won't cause much damage. Rather, it is prolonged periods of flooded soil that cause problems. Although some plants, like willows, bald cypress, flag iris, and other bog plants, can adapt to long periods of floodwaters, most plants cannot; some can handle as little as a few days.
Symptoms of Water Damage
Symptoms of water damage can be hard to identify because they can look just like many other plant problems. Symptoms will generally first appear on the leaves. In trees and shrubs, however, symptoms may not manifest for a year or more, so keep watching especially if other nearby plants are exhibiting symptoms of damage. Signs your plants have been damaged by waterlogged soil include:
- Yellowing leaves
- Twisting leaves
- Dropping leaves
- Soft, spongy areas at the base of the leaf
- Wilting despite plenty of water
- Roots turning dark, often with a rotting odor.
- Lack of flowers or fruits
- Shoot dieback
Several factors determine how much damage is done to plants by flooding, including how long the soil is waterlogged, whether it is fresh or saltwater, the time of year and the type and age of the plant. Flooding during warm weather is more damaging to plants because they are actively respiring and need more oxygen than during cold weather.
What to Do
Unfortunately, once the soil is flooded, there is not much you can do but be patient. Many plants that show signs of distress during a flood may eventually recover. In the meantime:
- Don't walk on the waterlogged soil. You will just compact it and cause more damage to distressed roots.
- If the plants were underwater, clean them off with a hose, to remove any sludge and other residues.
- Keep an eye out for diseases that will take advantage of stressed plants. Fungal diseases, in particular, favor damp weather.
You can purchase a relatively inexpensive soil moisture meter at most hardware stores. A meter will tell you the percentage of water remaining in your soil. If you still have mud, you won't need a meter to tell you the soil is waterlogged. However, if you are wondering if it is dry enough for the roots to get the necessary oxygen, a meter will tell you when the soil has reached that level (usually between 40 percent and 70 percent).
Fortunately, you have more options for protecting and supporting your container plants.
- If the waterlogged plant is in a container and you can't move the container somewhere sheltered, take the plants out of the container and let them sit and drain on newspaper or cardboard overnight. Once they have dried enough to see the roots, prune off any that feel slimy, before repotting in dry soil.
- Potted plants that have been contaminated with sludge are best disposed of.
- Empty and clean pots, water trays and saucers, then wash them in warm soapy water.
- The soil in flooded containers will have lost most of its nutrients and will need a new dose of fertilizer. Use a slow-release organic fertilizer, to release the nutrients over time, as the plants recover.
Protecting Your Plants
If you live in a flood-prone area, it's wisest to design your gardens to withstand flooding. There are a number of ways to do this; some are easier and less expensive than others.
- Raised beds: Your plants will still be susceptible to flooding, but will drain and warm faster.
- Permeable hardscaping: Instead of impermeable surfaces like concrete, consider hardscaping with gravel, sand, and other permeable surfaces. These will allow more drainage on driveways and patios, limiting runoff.
- Green roofs and rain gardens: While these can take some time and money to set up, they are environmentally-friendly solutions that slow runoff and filter impurities.
- Dig a pond: While this is probably the most labor-intensive option, it can also be very effective. A pond, along with a graded landscape, can divert the runoff to a holding area where you can welcome water-tolerant plants.
- Choose water-tolerant plants: If you live in a flood zone, why keep fighting it? Consider planting your garden with plants that love the water!
Managing a Garden after a Flood. West Virginia University Extension