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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Flooding Stress on Plants FAQ's

This article was published originally on 6/16/2008

This year has certainly made the record books for snow and ice this winter and water this spring. Many of our landscape plants were slow to emerge due to the long winter and the cool weather this spring. And those that did fully leaf out are now under several inches (or feet) of water in some locations. This "one-two punch" will certainly have a negative effect on some of the plants in your landscape. What can you do? Unfortunately there is nothing you can do to change the weather. There is not even a lot you can do if your garden or landscape was flooded. At least, not until the water recedes. While many landscape plants will survive short periods of flooding, extended periods of standing water are often detrimental because of declining levels of oxygen in the soil. As soon as possible, remove flood debris, such as plastic containers, wood, and plant debris, from the landscape. If additional soil or sediment has been deposited on lawns or over tree root systems, removal may be necessary. One inch of silt or soil is sufficient to kill a lawn. Silt deposits of 3 inches or more can be injurious to trees. What about damage to a vegetable garden? If a garden was destroyed in the flood, there is still time to plant some replacement vegetables. Vegetables like snap beans, cucumbers, summer squash, sweet corn, and several other crops will still have time in the remainder of the season to produce normal yields. It may be possible to salvage some vegetables in the garden if the plants survive the flooding. Leafy vegetables, such as lettuce and spinach, should be pulled and discarded. Flood waters likely contain potentially harmful microorganisms and leafy vegetables are difficult to wash completely. Vegetables that produce fruit (tomatoes, peppers, eggplant, cucumbers, etc.) should be safe to eat by the time they are mature. For additional safety wash the fruits thoroughly before eating. When will I know if my plants are okay…or not? You should know if vegetable and flowering annuals survive within one to two weeks. These plants do not have large storage reserves, therefore, they will show damage first. With woody plants, the wait may be much longer. After the floods of 1993, it took a couple of years for some trees to either fully recover from the floods or die. Survivability depends greatly on the species and the site. Symptoms of stress for trees and/or shrubs can seem relatively minor with leaf yellowing, reduced leaf size and shoot growth, and sprouts along the stem or trunk, to fairly obvious stress symptoms such as crown dieback, early fall coloration and/or leaf drop, and large seed crops in years to come. Are there any plants that are more likely to survive flooded or wet soils? Certainly, there are even plants that will tolerate standing water…all the time. Bald Cypress (Taxodium distichum), Alders (Alnus species), Willow (Salix species), and River Birch (Betula nigra), will easily survive standing water and are often planted along edges of ponds. Other trees that should tolerate brief periods of saturated or flooded soils without injury are Red Maple (Acer rubrum), Boxelder (Acer negundo), Sycamore (Platanus occidentalis), and Cottonwood (Populus deltoides). A few herbaceous perennials that prefer moist or wet soils include: Yellow Flag (Iris pseudocorus), Joe-Pye Weed (Eupatorium purpureum), Spiderwort (Tradescantia species), Cardinal flower (Lobelia cardinalis), Ligularia (Ligularia species), Hardy Hibiscus (Hibiscus species), and tender perennials like Canna (Canna xgeneralis) and Calla Lily (Zantedeschia hybrids). Plants that are most likely to be damaged by flooding are: many species of evergreens such as Pine (Pinus), Spruce (Picea), and Fir (Abies), many Oak (Quercus) species, Sugar Maple (Acer saccarhum), Crabapples (Malus species), Redbud (Ceris canadensis) and Magnolias (Magnolia species). A few herbaceous perennials that do not tolerate wet soils include: Lamb’s ear (Stachys byzantina), Butterfly weed (Asclepias tuberosa), Russian Sage (Physostegia atriplicifolia), Stonecrop (Sedum species), and many spring flowering bulbs like Daffodils (Narcissus), Tulips (Tulipa), Crocus (Crocus), and Hyacinth (Hyacinthus). For more information on flooding resources, including flooding effects on plants, check with your local county extension office. 

Year of Publication: 
2008
Issue: 
IC-499(11) -- June 16, 2008