Ask The Hort Agent: Flood-like Conditions & Plants

  • Posted: Friday, July 26, 2013 10:12 a.m.

Question: How are the flood-like conditions going to affect plants?

Answer: Newton’s third law of motion says, “For every action there is an equal and opposite reaction.” While Newton may have been talking about things that are moving, you can bet the excess water is going to cause a reaction. The type of reaction is going to depend on several factors. The first factor is the type of plant. Large perennial plants like trees and shrubs will suffer if their roots are immersed in water for long periods of time. Ironically, the symptoms they display will be similar to drought symptoms. Roots need water, but they also need air. Too much of either one is harmful. Poplar trees will be the first ones to start showing yellow leaves. Trees and large shrubs may also have delayed reactions that are not visible until weeks, months or even years later.


Standing water typically has a quicker effect on other plants. The result is excessive wilting. Prolonged water exposure will result in permanent wilting (death). Smaller shrubs and perennials will also suffer from increased disease potential. Diseases which are blown from Florida each year often rely on wind and humidity to thrive. The stalled low pressure system that delivered all the rain also carried diseases in the air straight up the east coast. Anthracnose and mildew diseases are thriving in these conditions.

In addition to foliar diseases, soil born diseases are worse during wet conditions. These problems didn’t ride the wind from Florida. They were already here. While wind doesn’t spread them, flooding does. Erosion and excessive water can spread soil born diseases around a field or landscape. People always blame hurricanes for bringing in insects, animals and weeds. While this is rarely true, wet systems can usher diseases into new areas.

Annuals, both ornamental and vegetable, are also being hit hard by diseases. In addition to disease problems, annuals are also suffering from fertilizer leaching. Squash, bean, cucumber and other vegetable plants will be smaller and paler if nitrogen has been washed away.

The next factor which will determine the effect of all this rain is the soil. People using raised beds will fare the best. This is especially true if the raised bed towers 6 or more inches over the soggy soil. Believe it or not, folks with raised beds may even have to irrigate if they get 4 or 5 days without rain.

If your property is perched on a well drained site, then the rainy weather will probably have little effect on your plants. The opposite is also true. Flat and low areas will be suffering. Soil type also plays a role. Clay soils will hold water tighter and longer. Sandy soils will not have any problems if there is a place for the water to be drained away.

For more info about flooding damage, check out http://tinyurl.com/mzgysha For some tips about helping flooded trees, visit http://www.uwex.edu/ces/ag/issues/effectsoffloodingonplants.html If you do not have internet access, then call me at 910-893-7530 or email me at gpierce@harnett.org

I’m no carpenter, but I feel the need to build a large boat. While I’m not sure how the trees will fare in the flood, my two dogs and two cats are going to have a tough time. Since they have been fixed, they probably won’t be allowed on the boat.

Gary Pierce

http://www.harnett.org/coop/horticulture-programs.asp

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