However, this concept needs modifying when applied to soybeans. Soybean varieties respond much differently to delayed planting than either corn or sorghum hybrids. The shift from the vegetative to the flowering stage in soybeans is caused mostly by changes in the length of darkness. Adapted varieties flower soon after the dark period begins to lengthen in late June. Soybean flowering is also influenced to some extent by temperature.
High temperatures hasten flowering.
Given a very warm vegetative period, flowering can start before the dark period begins to lengthen. Since flowering response of corn and sorghum is more temperature dependent than that of soybeans, accumulated growing degree days are reliable for estimating corn and sorghum growth stages but not for estimating soybean growth stages. Planting Date Considerations Soil temperature is an important aspect. Planting into seedbeds that are in the low fifties is not advisable unless soil temperatures are rising rapidly. Sixty degrees Fahrenheit is a good target at which to begin planting.