Sorghum-sudangrass is a warm-season annual grass, a hybrid developed from a cross between forage sorghum and sudangrass. This fast-growing plant is highly valued in agriculture for its ability to produce substantial biomass, making it a popular choice for forage and cover cropping. Its deep root system and tolerance to heat and drought allow it to thrive during the hot summer months when cool-season forages struggle. Knowing the optimal planting window is paramount for maximizing yield potential and ensuring a healthy, uniform stand. The timing of planting dictates successful germination, quality, and quantity of the harvest.
Temperature Requirements for Successful Germination
The single most determinative factor for planting sorghum-sudangrass is the soil temperature. As a tropical grass, it is sensitive to cold and requires a consistent soil temperature of at least 60°F, with 65°F preferable for rapid emergence. Planting should be delayed until this threshold is reached and is expected to remain steady, typically about two weeks after the ideal corn planting date in a given region.
Planting into cold soil significantly slows germination and emergence, which can take up to two to three weeks instead of the typical three to seven days in warm conditions. This extended vulnerability exposes the seed and seedling to increased risk from soil-borne pathogens and insect damage, leading to poor and uneven stand establishment. Chilling injury from cold temperatures can stunt the plant’s growth early on, permanently affecting its overall productivity.
The most accurate way to determine the safe planting window is by measuring the soil temperature directly at the intended planting depth. This measurement should be taken in the morning, reflecting the soil’s minimum daily temperature. Relying solely on ambient air temperature can be misleading, as air temperatures may warm up while the soil remains too cold to support vigorous seedling growth. A consistent soil temperature above the minimum for several consecutive days confirms the soil is sufficiently warm for quick emergence.
Planting when the soil is reliably warm ensures a quick start, allowing seedlings to rapidly develop a strong root system and shade the ground. This quick growth maximizes the plant’s ability to scavenge nutrients and outcompete early-season weeds. Waiting for warm soil conditions is rewarded with a healthier, more productive stand than rushing an early planting.
Strategic Planting Based on Intended Harvest Use
While soil temperature dictates the earliest safe planting date, the crop’s ultimate purpose guides the optimal strategic planting date. The window for successful establishment can extend well into the summer, often until mid-July or early August, depending on the length of the growing season before the first frost. This wide window allows producers to tailor planting times to their specific harvest goals.
When the goal is maximum biomass accumulation for hay or silage, planting should occur as soon as the minimum soil temperature is met, typically in late May or early June. An early start is necessary to allow for multiple cuttings, which require approximately 45 days of growth per cut. Achieving two or three high-yielding harvests before the first killing frost requires a longer overall growing season.
For livestock grazing, a staggered planting schedule is often employed to ensure a continuous supply of fresh forage throughout the summer. Delaying a portion of the planting until mid-summer can provide lush grazing during the later months when cool-season pastures enter their summer slump. For safety, grazing should not begin until the plants are at least 18 to 24 inches tall to minimize the risk of prussic acid poisoning.
Planting for use as a cover crop, particularly following the harvest of a main crop, generally occurs later in the summer. Sorghum-sudangrass is an excellent choice for a late-season cover crop, but it requires sufficient time to establish a dense canopy. A minimum of six weeks of warm growth is needed before the expected first frost to produce enough biomass to suppress weeds and improve soil structure.
Essential Seedbed Preparation and Soil Conditions
Successful planting depends not only on when the seed goes into the ground, but also how and where it is placed. Before planting, the seedbed must be firm, clean, and well-prepared to ensure uniform seed-to-soil contact, which is necessary for consistent moisture uptake and emergence. A firm seedbed prevents the seed from being placed too deep and allows for the rapid capillary movement of water to the seed.
The ideal planting depth for sorghum-sudangrass is generally shallow, ranging from 0.75 to 1.5 inches. In drier conditions or sandy soils, the seed may be placed slightly deeper, up to 2 inches, to ensure it reaches adequate soil moisture for germination. Planting too deep will exhaust the seedling’s energy reserves before it can emerge from the soil.
Sorghum-sudangrass performs best in well-drained soils, as it does not tolerate waterlogging or ponding. While it tolerates a wide range of soil pH, the optimal range for maximizing nutrient availability and growth is between 6.0 and 7.0. Adequate soil fertility, particularly nitrogen, is necessary to support the rapid growth and high biomass production expected from this crop.