Sorghum, often called milo, is a resilient cereal grain grown globally for diverse purposes. As a warm-season crop, it thrives in hot, dry conditions where other grains may fail, allowing cultivation across a wide range of environments. Sorghum serves as a major source for human food, livestock feed, and the production of ethanol. Determining the exact moment to harvest is driven by the intended use of the crop, which dictates the desired moisture content and maturity stage.
General Timing of Sorghum Harvest
Sorghum planting typically occurs in late spring or early summer, generally around May or June in temperate climates, once soil temperatures have warmed sufficiently. This timing ensures the plant has a long, warm growing season for full development. The total time required from planting to harvest for most grain varieties ranges from 100 to 140 days, a duration that is highly dependent on the specific hybrid and local climate conditions.
The overall harvest season in major production areas usually spans from late summer into the fall, most commonly from September through November. Producers must carefully manage the planting date to ensure the crop matures before the first hard frost, which can stop the final stages of grain development. This relatively short growing cycle allows sorghum to be a flexible option, sometimes used as a double-crop following an earlier harvested winter grain.
How Sorghum Type Affects Harvest Schedule
The final application of the sorghum plant creates the largest variance in harvest timing, as different parts of the plant are prioritized. Grain sorghum is harvested only after the seeds have reached physiological maturity to maximize the dry weight of the grain. This harvest is typically performed mechanically when the grain moisture has dried down to a level suitable for combining.
Forage sorghum, grown for silage and livestock feed, is harvested much earlier, focusing on maximizing digestible biomass. The ideal time for cutting is at the soft dough stage of the kernel, when the plant is still green and high in moisture. Harvesting at this stage ensures a high concentration of total digestible nutrients, as delaying the harvest increases lignin content and reduces the feed’s quality.
Sweet sorghum is cultivated specifically for the high sugar content found within its stalks, which is processed into syrup. This variety is harvested when the stalks have reached their peak sugar concentration, often before the seeds are fully mature. The timing is calculated to maximize the liquid sugar yield, a metric different from the dry weight of the grain or the overall biomass.
Key Indicators of Crop Readiness
For grain sorghum, the most definitive signal of physiological maturity is the formation of the “black layer” at the base of the kernel. This dark spot appears where the kernel connects to the plant, sealing off the flow of nutrients and moisture from the plant to the seed. Once the black layer has fully formed, the grain has achieved its maximum dry weight and will not gain any further mass.
When the black layer forms, the grain moisture content is relatively high, typically ranging between 25% and 35%. Prior to this stage, visual cues like the change in the head’s color from green to its final bronze, red, or white hue indicate that maturity is approaching. Additionally, the kernels will reach the hard dough stage, where they can no longer be easily dented with a fingernail.
Moisture Management and Storage Timing
Although the black layer signals the end of the growing cycle, it does not mean the grain is ready for immediate harvest by machinery. The moisture content must drop significantly before the grain can be safely stored long-term without spoiling. For safe, extended storage, the moisture content of sorghum grain must be dried down to a range of 12% to 14%.
The required dry-down from 25–35% to 12–14% often takes several weeks in the field, with the rate dependent on temperature, humidity, and airflow. Waiting for the grain to dry completely in the field risks losses from shattering, lodging, or damage from birds and weather. For this reason, many producers harvest the grain earlier, often around 20% moisture, and use mechanical drying equipment to reduce the moisture content to the required storage level.