When considering soybeans for a deer food plot, land managers balance the high protein forage offered in summer with the high-energy grain provided in late fall and winter. Soybeans are an attractive food source due to their nutritional profile, which supports antler growth and fawn development. Planting soybeans late in the season significantly risks the plot’s success, making the timing of the last possible planting date a crucial decision. The challenge is ensuring the plant has enough time to develop before its life cycle is naturally cut short.
Understanding Maturity Groups and Photoperiod
The latest date a soybean plant can be successfully established depends almost entirely on the specific variety chosen, categorized by its Maturity Group (MG). The MG system ranges from 00 in the far north to IX in the deep south, indicating the latitude to which the variety is best adapted.
Soybeans are highly sensitive to photoperiod, meaning their transition from vegetative growth to flowering is triggered by the shortening of daylight hours. This mechanism determines when the plant begins to produce pods and seeds. If a variety adapted for a long growing season is planted too late, shortening days will trigger premature flowering, resulting in a short, underdeveloped plant with little biomass. Selecting a variety with a shorter maturity window than the regional standard is necessary when attempting late planting.
Calculating the Latest Viable Planting Window
For food plots, late planting shifts the goal from maximizing grain yield to maximizing palatable vegetative growth and available biomass for browsing. The latest viable planting date is defined by two limiting factors: the “safe cutoff date” for adequate forage production and the average date of the first killing frost. Soybeans planted late have a shorter period for vegetative growth, resulting in physically shorter plants with fewer nodes and pods set lower to the ground.
In the Northern Tier and upper Midwest, the latest planting window for forage soybeans typically closes around late June to early July. Planting after this period increases the risk of the first killing frost damaging the plants before they accumulate sufficient protein-rich leaf matter. Moving south into the Mid-Atlantic and upper South, the window extends slightly, with successful planting sometimes occurring into mid-July, often utilizing shorter-season varieties.
In the Deep South, where the growing season is much longer, the planting window can extend into late July or even early August for maximum vegetative growth. However, planting past the third week of July is ill-advised, as the photoperiod effect will dramatically reduce the time available for the plant to gain height and canopy density. The general rule is that for every three to five days planting is delayed, the final maturity is only delayed by about one day, which drastically shortens the overall growing period.
Management Strategies for Late-Season Plots
Because late-planted soybeans experience a compressed growing cycle, specific management practices are necessary to ensure rapid establishment and survival.
Increased Seeding Rate
One effective compensatory measure is increasing the seeding rate by at least 10 to 20 percent when planting is delayed past early June. This higher plant population helps compensate for the shorter stature and reduced branching of individual plants. It also encourages faster canopy closure and better light interception.
Soil Fertility and Weed Control
Adequate fertilization is paramount for pushing rapid growth in a limited timeframe. Late-season plots demand excellent soil fertility, specifically phosphorus and potassium, to support quick biomass accumulation. Weed control is also critical, as the canopy may not close quickly enough to suppress aggressive late-summer weeds, requiring timely herbicide application.
Moisture Management and Spacing
Late planting often coincides with the hottest and driest period of the summer, making good seed-to-soil contact and consistent soil moisture crucial for germination and emergence. If planting in dry conditions, planting depth must be carefully managed to place the seed into uniform moisture. Row spacing should also be narrowed to 15 inches or less to encourage the plants to cover the ground faster.
Extending Plant Life
Extending the plant’s life during reproductive stages through the use of fungicides and insecticides can help offset the yield loss associated with a shorter season.