Gardens After Flooding

Why does it seem like our community floods more often than it used to?

Think about what your community was like 10, 20, 50, or even 75 years ago. In the past, forested or agricultural lands absorbed most of the rain. Impervious surfaces, like homes, businesses, parking lots, streets, and sidewalks, cover many of our communities. Our closely mowed lawns barely absorb heavy rains. Most heavy rain dashes downslope until it reaches a storm drain, stream, or river. Add to that an increased number of severe rainfall events each year, and floodwaters become more commonplace.

What can we do to manage stormwater on our properties?

There are many strategies to reduce the amount of stormwater in our communities. Do your best to reduce impervious surfaces and allow rainfall to soak into the earth. Start with several easy techniques. Use rain barrels to gather the rain for use another day when plants need it. Redirect downspouts to rain gardens. A rain garden is a depression where runoff collects and soaks into the ground in less than two days. It is not a pond! Many plants tolerate the wet-dry conditions in the lowest part of the rain garden. Think of it as a beautiful, shallow bowl-shaped flower bed that reduces runoff!  (See An Introduction to Rain Gardens; Rain Gardens - the Basics; and Rain Gardens - the Plants.)

Consider converting some of your closely mowed lawn to a meadow. These taller plants have deeper roots to hold the soil in place and slow down the runoff. If a stream or creek is nearby, avoid mowing to its edge. Planting trees and shrubs will stabilize the stream bank, slow runoff, and increase water infiltration to restore drinking water in the aquifer. Use live-staking to add shrubs, which is easy and economical.

How should I treat my flooded lawn?

If your lawn is flooded in the early spring, turfgrasses can withstand several days of submersion without serious damage. The damage is done by a lack of oxygen and light. However, later in the summer, when temperatures are high, ponding water can cause damage or even loss within a few hours, mostly due to high water temperature.

Once the floodwaters have receded, pick up any debris from the lawn. This is essential as the deposited debris is a safety hazard to persons operating equipment, like mowers.

As soon as the lawn is dry, and this can take many days or even weeks, aerate it. If the soil temperature remained below 60°F and the water remained for four days or fewer, the turfgrass will probably recover. If the lawn was submerged for longer, repeat aeration in the autumn, and the following spring. Break up the aeration cores and over-seed in the autumn. Pre- or post-emergent herbicides may be needed to treat weed seeds that have come in with silt deposits. (See also Repairing Lawns Following Flooding; Caring for Flooded Lawns)

What effect does flooding have on trees and shrubs?

It is very difficult to determine the long-term effect of being underwater on trees and shrubs. Some woody plants tolerate wet soils better than others. All will suffer from a lack of oxygen when the floodwaters fill all the air spaces between the particles of soil. Usually, landscape plants can withstand being submerged for about a week. Remember that the waterlogged root systems may be affected by floodwater, even though the soil surface has begun to dry. This makes them susceptible to root-rot diseases. (See After the Flood: Garden and Landscape Plants.)

There is not much that you can do about flooded trees and shrubs except wait and hope for the best. Watch for signs of dieback: yellowing and dropping leaves. But, again, be patient. Just because the leaves drop does not mean that the branch or plant is dead. Often, the dropped leaves are a sign of stress, and the plant will re-leaf later in the summer. Live stems and buds will have some green tissue – look under the branch bark. Remove limbs that are dead or physically damaged.

I have worked hard to grow my vegetables. Can I eat the produce after the garden has been flooded?

This is a very difficult question to answer. The simplest and safest answer is a resounding, "No! You cannot eat produce from your flooded garden." The floodwaters may have come from pastures, sewage treatment facilities, and other sources of disease-causing contamination. Produce has too many nooks and crannies to thoroughly clean and disinfect. Cooking or preservation does not render it safe to eat. Fresh produce that was submerged by floodwaters should be discarded.

Seeds and young plants are unlikely to survive being submerged by floodwater. You will observe discolored leaves and stunted growth, or plant death.

However, if a flood occurs early in the growing season, it may be possible to salvage at least some of the garden produce.

All produce that is consumed uncooked or raw, e.g., spinach, lettuce, cabbage, should be discarded. Soft fruits, such as strawberries and all melons must be discarded. Flood-damaged garden produce that is unfit for eating should not be preserved, including freezing, canning, or dehydrating. The recommended processing and cooking time may not be sufficient to kill pathogens.

Early-season crops that will not be harvested for 120 days and have not been touched by floodwaters may be safe to eat if cooked or peeled. It must be completely intact, with no cracks or bruises. If you are unsure if flood water contacted the produce, throw it out!

Late-season vegetables that come from flowers produced on growth that develops after floodwaters recede should be safe.

You can replant after the soil has fully drained and the top two to three inches of soil have completely dried. Plants that can be started later in the late gardening season after the flood should be safe after an early spring flood. Cover crops can be established on flooded gardens to remediate the soil for the next growing season, rather than letting it lie fallow.

When your landscape floods, be patient. Many plants will recover over time. Again, where edible plants are concerned, the safest response is also the simplest: "No! You cannot eat produce from your flooded garden."

Additional Resources

Food Safety Modernization Act - USDA

Food Safety for School and Community Gardens (PDF) - North Carolina State Extension

Food Safety for School and Community Gardens (PDF) - Virginia Cooperative Extension

Understand FSMA: The Produce Safety Rule - Penn State Extension