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How late can you plant corn & soybeans?

Traditional thinking says we're just about to the end of the time when corn can be planted and expected to turn out much of a crop at all. But do this year's unique conditions mean you can stretch that window a little later? It's far from the most savory prospect, obviously, and depends on a lot of major variables moving forward. However, if you've got the right conditions and contingencies if it fizzles for grain production, it may be an option.

First, you've got to have the right seed. Right now, planting a short-season hybrid's about a must. But those varieties may also have a tough time getting out of the ground depending on your location, says University of Illinois Extension crop specialist and agronomist Emerson Nafziger.

Projections based on data from the state of Illinois show you can expect about half your normal yield if you're planting corn between June 15 and 20. That's if conditions are optimal; if you run into trouble at any point, namely with moisture, you'll likely be looking at chopping silage.

"If we do plant corn in mid- to late June, planting a very early hybrid, having the option of harvesting the crop as silage if grain production looks unlikely, and getting good rainfall throughout the rest of the season will all improve the chances of ending up with a profitable crop," Nafziger says. "The chances of having enough frost-free days to grow a crop are higher in central and southern Illinois than farther north, but higher water loss rates and lower water-holding capacity of soils can cancel this advantage. It may also be difficult to get seed of very early hybrids, and because early hybrids are not developed for the central and southern Corn Belt, there is no guarantee that they will do well under late planting."

Even with a late frost date -- a critical variable to raising a crop if you're planting this late -- it's difficult to predict what kind of conditions you'll face between now and then. So ultimately, Nafziger says June 20 is about the last day he'd risk planting corn.

"I reanalyzed our more recent planting date data, and if -- this is a big 'if' -- we can accept projections of yield that go well past the last planting date, we would move the planting date from which we’d expect half a crop a little later, closer to the end of June. But we know that corn planted during or after the middle of June will produce fair to good yields in some years and very little yield in other years, depending on unpredictable weather that follows. So it makes sense to consider June 15 to 20 to be that last practical date on which to plant corn if we want to produce grain."

It's not just corn that's running late. A lot of soybean acres are left to plant, and the calendar's starting to run short for that crop, too. Projections based on U of I plot data show early July's the basic timeframe for a soybean crop to be planted in order to yield half of normal. That's for normal rotational soybeans; for double-crop beans, the window's different.

"There is one important difference between double-crop soybeans and soybeans that are planted late but don’t follow wheat harvest. Wheat removes a substantial amount of water from the soil as it matures, and in years with average June rainfall, the soybean crop that follows wheat has much less soil water available to it than does the crop that follows only the crop from the previous year," Nafziger says. "As is always the case, good rainfall through the rest of the season can cancel out this advantage, but it won’t eliminate it averaged over years."

And, if you're planting beans late, reconsider before making any major production system changes, Nafziger adds. Doing so rarely improves crop output.

"Soybean planted in mid- to late June needn’t be managed much differently than early-planted soybeans. Our recent research indicates that narrow rows tend to yield more regardless of planting date, and raising seeding rates seldom produces an advantage when planting late," he says. "Unless a late-maturing variety was the first choice, there is no advantage to changing to an earlier variety for late planting."

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