Be wary of plants sitting in water for too long

Published 2:00 am Sunday, February 12, 2012

I dutifully chastised myself for last week’s reference to planting tree seedlings during two days of monsoon-like rain. I had overlooked one of my own column rules: never speculate about weather yet to come between Wednesday’s deadline and Sunday’s printing.

It’s all slowly coming back to me now.

Other than canceling tree planting and plans a group of us had to prune the rose garden at the ag museum in Jackson, two days of winter rain were mostly harmless. OK, rabbit hunters and winter golfers got messed over, too.

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Later in the year, when soybeans, tomato plants and petunias are under our care, too much rain can be as bad as not enough. That’s because plants growing in saturated soil have the same problem as plants in soil gone too dry: they can’t get enough water. That’s right. Other than species “designed” to grow full time in water or wet soil, plants cannot get water through the roots if the soil stays too wet.

The roots we see when we dig up or unpot a plant are the ones that transport water and its dissolved food to the rest of the plant. However, it is the tiny, nearly microscopic root hairs that actually absorb water from soil. Water moves into root hairs by the process known as osmosis. For osmosis to take place, oxygen must be available around root hairs. This oxygen exits in the air spaces, i.e., pores, in soil. In super wet soil, the pores are filled with water and all the oxygen has been pushed out.

I know, I know water contains oxygen. But only gaseous oxygen can “osmosize” water into root hairs and thus into roots and on up above ground. So soil too wet too long causes plant leaves to curl and wilt and turn yellow and die just like what happens when there is not enough water. And for the same reason — not enough water getting in.

Here amongst the Mississippi and Yazoo rivers, we all-too-often see wet soil killing crops. To me, backwater-flooded corn is the real educator. For sure, underwater corn is a goner. But what about shoulder-high corn standing tall in ankle-deep water? Or corn completely out of the water at the muddy edges of the waterline? Aren’t the green corn leaves and sunny days doing the photosynthesis thing in spite of the mud? No. All plant processes, including photosynthesis, require water brought up by roots. And so we see corn die in the mud.

Gardeners, like farmers, have no control over rain or floods. But we do control hoses, sprinklers and the fanciest of decorated watering cans. It’s been rare, but I have seen instances of good intentions killing plants by overwatering. Don’t do that.

Lest I forget, there is one other thing that can happen when soil stays very wet too long. In the presence of certain bacteria, wet soil can produce toxic ethylene alcohol in roots. Then it becomes a matter of whether plants wilt from waterlogged thirst or because they are drunk!

Terry Rector writes for the Warren County Soil and Water Conservation District, 601-636-7679 ext. 3.