Sorghum is a grass crop, scientifically known as Sorghum bicolor, valued globally for its grain, forage, and sweet syrup production. This hardy plant tolerates drought and heat, thriving in conditions where other major cereals like corn might struggle. Successfully establishing a sorghum crop requires careful consideration of variety selection and ground preparation. This guide offers practical instructions for timing, depth, and the initial care needed to ensure a strong, healthy stand.
Choosing Your Sorghum Variety and Soil Prep
Selecting the correct sorghum variety depends entirely on the intended use, as different types have distinct growth habits. Grain sorghum is typically shorter in stature, bred to maximize seed head production, and is primarily used for food, feed, or ethanol. Forage sorghums, including sweet sorghum and sudangrass, are much taller, growing up to 8 to 15 feet, and are cultivated for silage, hay, or bioenergy because they produce a large amount of biomass.
Sorghum performs best in well-drained, loamy soils, though it can tolerate heavier clay soils. An ideal soil pH range is between 6.0 and 7.5, with a pH of 6.5 often considered optimal for nutrient availability. Soil testing before planting is recommended to accurately assess existing nutrient levels, particularly for nitrogen (N), phosphorus (P), and potassium (K).
Sorghum responds well to nutrient applications, especially in soils testing low for these elements. Nitrogen and phosphorus are particularly important for early establishment and root development; phosphorus is often banded as a starter fertilizer at planting. Field preparation should focus on creating a firm, clean seedbed free of large clods and existing weeds, achievable through conventional tillage or no-till methods.
Mechanical Planting Instructions (Timing and Depth)
The timing of planting is directly linked to soil temperature, which is a better indicator than the calendar date for this warm-season crop. Sorghum seed should only be planted once the soil temperature consistently registers at least 60°F (15.5°C) at the intended planting depth. Planting when the soil is cooler than this threshold significantly slows emergence, increasing the risk of seedling mortality from disease and pests.
The optimal depth for planting sorghum seed is generally between 1 and 2 inches (2.5 to 5 cm) to ensure good seed-to-soil contact and access to moisture. This depth must be adjusted based on soil type and moisture conditions. Planting should be shallower in heavy clay soils, which can crust easily, and deeper in sandy or dry soils to reach adequate soil moisture. Placing the seed into firm, moist soil is important for rapid and uniform germination.
Plant population density and row spacing should be determined by the variety chosen and the expected moisture conditions, as sorghum can compensate by tillering under lower population densities. Grain sorghum is often planted with a target population ranging from 25,000 to 90,000 plants per acre, with higher densities used under irrigation or high-rainfall environments. Row spacing can vary widely, from conventional 30-inch rows to narrower rows of 15 inches or less, with narrower spacing sometimes offering a yield benefit.
Forage and sweet sorghums, grown for biomass, are typically planted at a higher population to discourage tillering and promote a single, thick stalk for silage. Seeding rates for these varieties often range from 5 to 20 pounds per acre, depending on whether the crop is grown under dryland or irrigated conditions. Consistent seed placement and firm closure of the seed furrow improve stand establishment across all sorghum types.
Managing Seedlings and Early Growth
The period immediately following planting, through the first few weeks of growth, is when the sorghum plant is particularly vulnerable. Maintaining adequate soil moisture is essential during the germination and emergence phases, as the young plant requires water to establish its root system. Drought stress during this early stage can weaken the stand, making the seedlings more susceptible to other issues.
Weed control during the first 30 to 45 days after emergence is important, as sorghum is a poor competitor against weeds during its early growth. Weeds can cause yield loss if left unchecked during this critical period, which lasts until the plant reaches the five-leaf stage. A strategy often involves a pre-emergence herbicide application at or shortly after planting, requiring rainfall or irrigation to activate the chemical barrier in the soil.
If the initial stand is too dense, thinning the seedlings may be necessary to reduce competition for light and nutrients. Growers should monitor the emerging crop for early-season pests, such as wireworms and cutworms, which feed on the seed or young seedlings. Early detection of these pests allows for timely intervention, helping to preserve the target plant population.