All gardens need water, but what do you do when we get too much of a good thing? Floods and long-standing water can be devastating to a garden. How much damage is done will depend on the duration of the flood, the types of plants, the type of soil they are growing in and whether there have been any contaminants in the flood water.
When plants are subjected to water-logged soils for long periods of time, roots are deprived of essential oxygen. Water fills all of the pore spaces in the soil and roots can begin to suffocate and die.
Native trees are fairly well adapted to temporary deluges. They will generally recover with little observable damage. Large shrubs may also bounce back well. Perennials will need to be observed for awhile to see how they fare. Annuals will be the first to show stress, and the least likely to recover.
Vegetables and fruits are more susceptible to periods of water-logged soils. Neither appreciates wet feet for any length of time. Herbs are also resentful of wet feet. Many of our favorite culinary herbs originated in the Mediterranean and thrive in drier climates.
If you have had heavy rain for an extended period, or have experienced a flood, there are things you can do to help your garden recover:
Don’t work wet soil
Working wet soil can do long term damage to the soil structure itself. Soil particles can become compressed, increasing compaction and exacerbating drainage issues in the future. This damage is not easily or quickly repaired.
Allow the soil to dry out for several days. Push a trowel into the soil and wiggle it back and forth. If visible water is in the hole, or if the soil at the sides of the trowel looks glossy, wait a few more days.
When you do start working, use hand tools such as a spading fork. Tilling with an implement has more risk of compaction than lightly cultivating with a fork. If you must till, save it for drier days ahead.
Don’t rush to replant
Soil biology is damaged when soils are water-logged for long periods of time. Soil microbes that require oxygen to live may die off and those that survive without oxygen may flourish. These anaerobic microbes cause soggy soil to have that foul, sour odor.
This imbalance affects the availability of nutrients for plant use. The soil food web needs a chance to recover. This can happen relatively quickly if the soil was healthy before the storm. If sufficient organic matter, nutrients and minerals are present, beneficial soil biology will re-establish itself once oxygen is available again.
If you must replant quickly in the vegetable garden, support the soil biology with added compost, dried molasses, and perhaps added mychorrhizae. Many seeds will have a tendency to rot in soggy soils. Even though you want to re-establish your veggies, you should wait until a ball of soil can be squeezed in your hand and no water drops can be wrung out. Like a damp sponge, moist but not wet.
Don’t rush to prune
Stress from water-logged soil may cause some leaves on fruit trees and herbs to yellow and drop off, but the branches are not necessarily dead. New leaf buds will begin to grow in a few days. Wait until you are sure there is die-back before you prune.
Clean up the fallen leaves and any foliage that is rotting. They can harbor harmful fungi and bacteria that could affect plants.
Heavy rainfall can leach nutrients out of the soil. A light fertilization will replace those nutrients. Don’t overdo it. It is better to fertilize lightly several times than to push plants that are recovering from stress. Foliar feeding with Ocean Harvest or seaweed extract can quickly boost needed minerals to reduce plant stress.
Use only slow-release, organic fertilizers that provide micronutrients and minerals in addition to the macro-nutrients, N-P-K. Epsom salts provide essential nutrients, magnesium and sulfur. In addition to aiding the uptake of other nutrients, these can help reduce plant stress. Broadcast over the new seedbed at a rate of 1 cup per 100 square feet.
Be prepared to deal with pests and disease
Water stress weakens plants. Weakened plants are susceptible to attacks. Fungal diseases are common after periods of heavy rain. Pull mulches back from the base of fruit tree, herbs, and vegetables until it dries out. This will decrease the opportunity of fungal disease spores to form and splash on leaves. It also helps the soil dry out faster.
Be prepared to take quick action with organic-approved fungicides and pesticides. It can be as simple as a baking soda and vinegar mix. Fire ants are likely to raise their nests out of the water-logged soil. Use the Organic Fire Ant Solution when they are observed.
Make an action plan
One of the best things you can do after a heavy rain is to assess your landscape. There is no better time to identify problem areas and form a plant to prevent future issues.
Get a clipboard and a camera or your cell phone. Walk the garden making notes and taking pictures of places where water stands for long periods of time. Use this information to help you make future decisions such as raising beds, improving soil texture, and making future plant selections.
You may find areas where all that is needed is increased drainage in your soil. Use a permanent material such as expanded shale. This material increases porosity, which makes a healthier soil as well as improving drainage at soil level.
You may decide that you need to seek the advice of a landscape professional if you find that drainage pathways are blocked by landscaping. They can often resolve these issues without destroying beds you have already established.
Make a list of plants that seem more sensitive to wet soils. Like it or not, storms and floods are likely in our area. If you have to replace plants, you may want to look for something better adapted to the possibility that it will happen again.
Dealing with contaminated storm water
If your garden has been inundated with city storm water, chances are you will have to deal with contamination issues. This water is often contaminated with raw sewage and hydrocarbons if the storm water infrastructure has been breached or if you live near a major highway.
If you have seen visibly contaminated water, such as a sheen of oil on the surface, consult a professional. You will need a professional soil test from a laboratory that can identify the contaminants and help you assess the situation and develop a remediation strategy.
Do not harvest and eat vegetables or fruits that are growing in the inundated garden. Washing and boiling may remove bacteria, but it will not remove industrial or roadway contaminants.
All is not lost in this case. There are natural bio-inoculants that digest hydrocarbons. Time and good soil biology will deal with sewage exposure. You can actually start with “washing” the garden. Hose down everything to remove mud and surface contaminants. You can follow this with a foliar feeding that includes compost tea in the solution. There are studies that show this helps colonize the leaf surfaces with beneficial microbes – a first line of defense against environmental pollutants.