Planting date. Planting date (both too early and too late) can reduce soybean yield potential. In 2013 and 2014, we conducted a planting date trial at the Western Agricultural Research Station near South Charleston, Ohio. In both years, soybean yield decreased by 0.6 bu/ac per day when planting after mid-May. The greatest benefit of planting May 1 to mid-May is canopy closure which increases light interception, improves weed control by shading out weeds, and helps retain soil moisture.