Agronomists advised: "You'll be better off if you leave the seed corn in the bag"
On April 26 the extended weather forecast was for cold, wet weather beginning May 1 or May 2. On April 29 and 30, the ground was dry enough in some fields and soil warmed up to 50 degrees or more. Farmers had to decide -- should I go ahead and plant on April 29 and 30 even though the temperature is expected to drop like a rock, and snow and rain are forecast for the next five to seven days?
The answer from the agronomists: You will be better off if your seed corn stays in the bag. Wait till next week to plant after the weather warms up and soil conditions improve.
So what does cold, wet weather do to corn seed sitting in soil, covered with snow?
Does snow insulate the ground and hold the temperature at a little higher level than it would be if the ground didn't have a snow cover? "Of course, cold, wet weather isn't an ideal situation for early May," notes John Holmes, Iowa State University Extension field agronomist in north-central Iowa. He explains what takes place underground with seed germination for corn in the early stages of development.
When you plant, the corn seed will imbibe water, says Holmes. If that cold water gets into the seed, it's a shock to the new seedling. The cold water stresses the seed. That sometimes stops the seed development process or slows it down, weakening the seedling considerably.
If everything goes according to plan, how long will it take for the seedling to emerge? It can be up to three weeks if the soil and weather stay cold, says Holmes. But usually it takes about a week and a half after planting for corn to emerge.
Here's how he figures this: It takes 125 to 150 growing degree days from corn planting to emergence. "We don't get many 'heat units' or growing degree days accumulating this time of year," he says. "If we get 10 per day, we're fortunate." That figures out to about 15 calendar days from planting to emergence.
What if cold weather or hard freeze hits emerged corn plants?
Holmes reminds corn growers that seed corn today is well- protected with fungicide seed treatments. That's a plus, having fungicide seed treatment to help protect seed when seed is sitting in soil waiting for a warm-up to 50 degrees F or higher.
Luckily, not much corn was planted and only a few fields had emerged in Iowa as of May 2 and 3. If we have more cold weather or a hard freeze, what can happen to the emerged corn plants?
The growing point inside the corn plant is still belowground at this growth stage. So the corn seedling will freeze off down to the soil surface. But the plant will shoot new leaves, regrow and keep coming up. The real concern with frost is if you have leaves fairly well developed, they can become "tied up" at the top of the seedling affected by the frost. The new growth of the recovering corn plant can't emerge through that wad of tied-up leaves. You need to keep an eye on such fields and check germination and emergence. You may need to replant.