Every year along about this time, I have farmers asking me if it is too late to plant full season soybeans.

Every year along about this time, I have farmers asking me if it is too late to plant full season soybeans. I have written about this several times over the years, but the topic always seems to be pertinent to the current year so here it is again.  Of course, there is no way to know for sure my answer is going to be one hundred percent correct because there are so many environmental and management factors that can alter how fast those soybeans are going to mature.  However, there is some research that has been done that does clarify this to a certain extent.
The research information I refer to when writing on this subject was generated at the Parsons Research Center, by Ken Kelley, Crops Research Agronomist at the center. His work was done back in the early to mid eighties and though the research was done quite a number of years ago, I think it is still valid when looking at the results from the different maturity groups.  Ken’s research addressed the issue of how the planting date affected the yield and date of maturity for the various soybean maturity groups.
Ken used five different maturity beans at five different planting dates over a period of five years.  The beans ranged from a late group three to a late group five.  The planting dates ranged from a late May planting to a mid-July planting.  The most striking thing is that yields between maturity groups at different planting dates did not vary that much.  The yield of all the maturities dropped considerably in the mid- July planting.
A very real problem quickly becomes evident when looking at the affect of the later planting dates with full season varieties.  The date of maturity of the group five soybeans is pushed back into late October and even the first half of November.
This factor brings two things to mind.  First of all, many farmers like to plant wheat after beans.  If the beans can’t be harvested until November, then planting to wheat may not be possible.  Secondly, later maturing beans planted late may be subject to early freeze damage.  We have  seen how adversely early freezes can affect our later planted longer maturity beans.
The bottom line based on this information is that full maturity beans should be planted in late May and early June.  Mid group fives can be safely planted through June 20 and early fives can be planted as late as July 1 without serious risk. However, after July 1, farmers need to consider dropping back to a late four.  After July 10, you probably should not be planting beans, but if you do, use a  mid group four.