Sorghum, also known as milo, is a warm-season grass crop cultivated globally for its grain, forage, and biofuel potential. Valued as the fifth most important cereal crop worldwide, it is known for its natural tolerance to heat and drought, making it a staple in semi-arid regions. Correct planting timing is essential to maximize the crop’s growth potential while avoiding environmental stresses and pest pressure later in the season.
Identifying Optimal Planting Conditions
The ideal planting date for sorghum is dictated by soil temperature. Sorghum seeds require a minimum daily soil temperature of \(60^\circ\text{F}\) at planting depth for germination. Planting should ideally occur when the soil temperature is sustained at \(65^\circ\text{F}\) and rising, with \(70^\circ\text{F}\) supporting the most rapid emergence.
Planting before this threshold increases the risk of poor germination and chilling injury. Cooler soils slow the seed’s metabolic process, extending emergence time. This slow emergence makes the vulnerable seedling more susceptible to soil-borne insects and diseases. Planting must also be deferred until after the average date of the last killing frost, as cold air temperatures can severely damage young plants.
Regional Planting Windows
The ideal calendar date for planting sorghum varies widely across the United States, following the seasonal warming trend from south to north. Growers in the Southern Plains (Texas and Oklahoma) often begin planting as early as mid-April or early May. This earlier timing allows the crop to mature before the most intense heat and drought of mid-summer.
In the Mid-South (Kentucky and Tennessee), the highest-yielding planting window typically spans from May 1 to June 1. Planting is generally delayed until late May or early June in the northern reaches of the Sorghum Belt. These later dates ensure the crop avoids late spring frosts and benefits from warmer soil conditions. Sorghum is also used in double-cropping systems, planted later in the season (late May through June) following the harvest of a winter small grain like wheat.
Necessary Preparations Before Planting
Hybrid selection should be based on the intended use (grain or forage), the maturity group, and appropriate pest and disease resistance, such as tolerance to the sugarcane aphid. The seed must be treated with a safener, like CONCEP, which protects the plant from injury when certain pre-emergent herbicides are applied.
The physical condition of the seedbed must be finalized before planting. Achieving a firm, weed-free seedbed is paramount for uniform seed-to-soil contact and successful moisture uptake. A pre-plant burndown or tillage operation is necessary to eliminate existing weeds, as post-emergence weed control options are limited. The seed should be placed at a depth of \(1.25\) to \(1.5\) inches, ensuring it rests in moist soil for successful germination.
Early Seedling Management
After planting, monitoring the field for stand establishment is necessary to ensure the target plant population is met. Seedlings are vulnerable to early-season insect pests during the first few weeks after emergence. Soil insects like wireworms and cutworms can damage the young root system or sever the plant stem.
The yellow sugarcane aphid and chinch bug also pose an early threat, injecting toxins that can stunt or kill small plants. Neonicotinoid seed treatments offer protection against these insects for about 30 days following planting. Post-emergence herbicides must be timed correctly, often before the sorghum plant reaches the five-leaf stage, to prevent competition and maximize yield.