Regardless of when you plant soybeans flowering still begins just after V3. The difference is the amount of foliage produced from VE to V3 with more foliage produced the earlier you plant.

Soybeans in Illinois can be planted over a 2- to 3-month period, from early April for full-season beans to early July for double-cropped bean. With soybeans being daylength sensitive, how will such a wide planting window and daylength impact when soybeans begin to flower?

With the delayed planting this spring, I began to wonder at what V-stage soybeans will flower as planting was delayed outside the normal April 15 to May 15 window. And then factor in planting double-crop soybeans after June 15 and how the late planting will impact at what V-stage soybeans begin to flower. I decided to investigate.

Soybeans are classified as indeterminate, semi-determinate or determinate in growth in the United States. Soybeans grown in Illinois and across the Corn Belt have an indeterminate growth pattern which means they will continue vegetative growth as they flower. Down south in the Delta and across the Southeast, they plant longer maturity determinate types which finish their vegetative growth when flowering begins. Click here to learn more about the two growth patterns and development staging.

Soybean development is staged using the Iowa State approach with V representing the vegetative stages and R representing the reproductive stages. Below is a general timeline for full season soybeans showing that flowering generally begins in the V3 to V4 stage regardless of calendar time. This means that if you plant soybeans between April 10 and May 15, they will all begin to flower at that same stage. Of course, we also know that at summer solstice on June 21, when nights begin to lengthen, flowering really kicks off for the next six weeks.

But what happens to development when double-cropped soybeans are planted after June 10 or 15? How will the V stage and R stages correspond?

John Pike, agronomist with Pike Ag LLC said, “With blooming triggered primarily through photoperiod sensitivity, beans planted substantially earlier would achieve more vegetative growth before blooming than a later planted (double-cropped) bean.”

Emerson Nafziger, professor emeritus at the University of Illinois at Urbana-Champaign explained, “Both photoperiod and temperature affect flowering date. The minimum vegetative stage to flower is about 3 trifoliolates (V3), and last year (2018) R1 was probably at about that stage for most planting dates due to consistently warm nights—plants didn’t have to wait until after the longest day to flower. In a more normal year, we’d expect to have more leaves at R1 the earlier the crop was planted, at least through mid or late May. Those planted later than that (June 1 or after) would likely flower as soon as they reached V3 or so, since the nights would by then would be long enough (and warm enough) to trigger flowering. In a year (like 2014) with a cool July, I’d guess that some plants were at V7-V8 before they flowered.”

G. Kelly Robertson, agronomist with Precision Crop Services LLC, emphasized that R1 will start right after V3-4 regardless of planting date for double-crop soybeans, but maturity group and environment will affect the length of time the plant flowers. “A Group 5 will flower multiple times, or each time a new node is put on during the growing season whereas a Group 2 produces flowers quickly and is done. I have seen Group 5 planted double-crop add a node and flower in September after a rain in years with prolonged growing seasons. These plants had “full pods” on the lower 2/3 of the plant. I have also seen group 4 beans planted double-crop get only knee high and be done flowering.”