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Cluster Flood

Water where there shouldn't be water

Does anyone need a drink? We have plenty of surface water for you at Wellfield if you want to stop in for a visit. Wellfield Botanic Gardens took a decent hit from flood waters, like other properties along Christiana Creek, the Elkhart River, and the St. Joe River in downtown Elkhart. Thankfully, there is little to no structural damage to be seen thus far, but what about ornamental plants and turf grass? How will they handle this record breaking event? What is the likely damage to garden plants and what to do about it? The answer, as always, is: it depends. Flood damage and your subsequent plan of action depends on time of year, duration of submergence, and species.

When flood waters move through, besides the obvious threat of erosion, a second threat is water saturation of the root zone. Roots need oxygen when actively growing (just like every other organism), and the average plant root pulls oxygen from the surrounding air spaces in soil macropores. As water percolates through the soil, it fills every available space, large and small, pushing out any gases ahead of it. It also pulls fresh air in behind it, acting as a vacuum, after a nice normal rain event. This does not occur when flood water moves through. Lack of oxygen results in the death of precious root hairs. Systemic root tissue necrosis results if the negative trend is prolonged even twenty-four hours in some cases.

This brings us to what time of year the flooding occurs, and what species are affected. If flooding occurs when the ground is still largely frozen or soil temperatures are still cool, there is much less chance of root damage. If roots are not actively growing, as they do in early spring and late fall, they are not consuming much oxygen and cell death is less likely. Warm up that soil, however, and the ball game changes. This is where the type of plant you are looking at factors in. Some garden plants could be obligatory or facultative wetland species, thus they can handle flooded conditions with relative ease. Your mesic and upland plants, however, might not do so well.

Are you biting your fingernails now? Sitting on the edge of your seat? Shall I give you a watered-down version of what to do, or can you concentrate on what comes next? The first step is to check the landscape once the waters recede. Look for exposed roots from erosion, any silt deposited, and signs for dead plants. Turf and perennials will show similar signs: leaf discoloration and nastiness below ground. If you suspect an herbaceous perennial, lacking leaves in early spring, has died, there are several simple tests you can do.

Small trees and shrubs can be subjected to the same tests, but for mature canopy trees such as oaks, I would recommend contacting your extension agent or a qualified arborist. As for Wellfield’s damage, time will tell, as the flood waters recede.

Josh Steffen
Horticulture Manager

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