Key Dates for Switching Maturities

Each day we turn the calendar, I receive more calls from Latham® dealers and farmers asking whether they should change maturities.  Keep in mind, the object is to achieve maximum yield potential for this crop.  When you switch maturities, you forfeit maximum potential and have essentially decided to lower your yield expectations!

Based on my experiences over the past 40 years – as well as research findings from many Midwest land grant institutions – I can tell you with confidence that full-season hybrids and varieties outperform early maturing hybrids and varieties.  Most people jump the gun and make the switch way too soon.  Corn planted in mid-June can make decent yields, and there’s no need to switch from corn to soybeans until after that.

There becomes a point in time where the advantages of planting a full-season hybrid diminishes to the point where shifting to a shorter-season hybrid or variety will generally result in drier corn and higher yields come fall.  Below is a summary of factors to consider when deciding whether to switch corn or soybean maturities.


I’ll use northern Iowa and southern Minnesota as an example.  If your maturity range is 98- to 109-days (which is what I use for the Latham Research Farm), then you should generally not deviate from those maturities until at least May 25.  If all you have left to plant is your 98-day hybrids, then you can safely extend your planting window to about June 7-10.  On the other hand, if you only have your 109-day hybrids left to plant, you’ll probably be better off switching to 95- or 99-day products.

That brings us to the next subject… if you must switch, how early of a hybrid is needed?  You don’t need to take it to extreme and switch from 109 RM to an 85-day hybrid or something equally silly!  Research has proven that it pays to stay closer to your “normal” maturity.  Switch to hybrids that are about 5 to 7 relative maturity units earlier than full season for the region.  Yields in this scenario will be greatly improved if northern Iowa and southern Minnesota farmers (from the example above) move toward a 92- to 95-day hybrid that is more closely adapted to the area.

The decision to switch maturity with delayed corn planting is difficult because of so many variables including: available GDUs, first frost date and fall drying conditions.  With this in mind, here are some general guidelines for Iowa farmers:

within Iowa
Full Season RMSwitch to
on May 25
Switch to
on June 10
South of U.S. 92114-117108-111105-109
North of U.S. 20100-10996-10594-100

For your convenience, below are few links to related articles: Adjust this information depending on where you farm, but make your decision is based on sound research and not “coffee shop facts.”  Just because your neighbor is switching doesn’t mean it’s the best decision.  Conduct a little research of your own before deciding what might be best for your operation.


There is absolutely no reason to start switching soybean maturities until at least mid-June.  I use June 20 as our cutoff here in North Central Iowa, but again, it depends on what you were planning to plant in the first place.  In this area, bean maturities range from 1.8 to 2.7.  L 2482 R2’s are still good to plant in this region until mid-June as we’ve done it before with great results.

Soybeans have even more resiliency when it comes to maturity stretch.  Because soybeans are more “photo period” sensitive, they actually adjust based on the length of the nighttime.  A planting date of June 20 in southern Wisconsin and June 15 in northern Wisconsin, using early maturing varieties, was considered to be the latest practical date by the University of Wisconsin.  Soybeans can be planted in our area as late as the Fourth of July with decent yield results as long as we don’t go into a dry period.

The 2019 planting season will certainly test our patience!  It’s tough to turn pages off the calendar without putting any seed in the ground, but it’s better to wait a few more days than to mud seed into the ground.  Experts warn that compaction and/or inadequate seed-to-soil contact from planting in wet conditions cause yield reductions for soybean farmers.  During a wet year, it’s even more important for soybean growers to pay close attention to machinery.  Avoiding soil compaction and obtaining good soil closure over seeds will help increase yields.  For more soybean planting tips to boost yields, click here.