Sorghum (Sorghum bicolor) is a highly adaptable cereal grass cultivated globally for its versatility. This single crop can be harvested as grain for food and feed, as high-volume forage for livestock, or as a source of sweet juice for making syrup. Maximizing yield and quality for any use depends entirely on precise harvest timing. Since the plant’s composition changes dramatically as it matures, knowing the correct cutting window ensures the highest return, whether measured by dry matter weight, sugar concentration, or kernel quality.
Universal Maturity Indicators
All sorghum types follow a predictable sequence of physical changes signaling the end of the grain-filling period. The kernel progresses from the milk stage to the hard dough stage, where the grain is firm and cannot be easily dented. At this point, the grain has accumulated roughly 75% of its final dry weight.
The panicle, or seed head, also changes color from green to its final shade (bronze, red, or tan). Physiological maturity is definitively reached when a dark spot, the “black layer,” forms at the base of the kernel. This layer signals that the flow of nutrients and dry matter into the grain has permanently ceased, though moisture content still ranges between 25% and 35%.
Use-Specific Harvest Timing
Grain Sorghum
For grain harvest, the primary concern is kernel moisture content to minimize loss and drying costs. Although grain reaches physiological maturity at 25% to 35% moisture, combining is impractical because the seeds are too soft for threshing. Harvesting above 25% moisture often results in cracked kernels and excessive unthreshed heads.
The ideal moisture content for combining is 20% to 25%, balancing reduced field losses and drying expenses. Growers in humid regions often harvest at the higher end of this range to avoid lodging, shatter loss, and mold, opting for mechanical drying. For safe, long-term storage, the moisture level must be lowered to 13% or 14% to prevent spoilage.
Forage/Silage Sorghum
When harvesting sorghum for silage or haylage, the goal is to maximize total digestible nutrients and tonnage by harvesting the entire plant. The optimal window occurs when the grain is in the soft dough to early hard dough stage. At this point, the plant has accumulated maximum starch while the stalk and leaves retain high moisture and digestible fiber.
The whole-plant moisture content should be 65% to 70% for proper ensiling. Harvesting forage above 70% moisture can cause nutrient loss through seepage and poor fermentation. If the plant is too dry, it is difficult to pack tightly, leading to trapped oxygen and poorly preserved silage.
Sweet Sorghum (Syrup)
Sweet sorghum is harvested for the sugar-rich sap concentrated in its stalks, with timing based on reaching peak sugar concentration, measured in Brix. The highest Brix reading typically occurs when the grain is in the hard dough stage, before the plant fully dries down. Juice sugar content at this stage often ranges from 15.5° to 16.5° Brix.
Harvesting too late can be detrimental, as increased starch content in the juice leads to crystallization issues during syrup processing. Harvesting must also be completed before a killing frost, which damages the stalks and negatively affects sugar quality.
Harvesting Methods and Necessary Equipment
Grain sorghum is collected using a conventional combine harvester, requiring specific adjustments to the header and cylinder. The header should be set high to minimize stalk material intake, and cylinder speed must be controlled to thresh the grain without cracking kernels.
Forage and silage sorghum are harvested using a specialized forage harvester, or chopper, which cuts the entire plant and chops it into small pieces for ensiling. This equipment handles the high volume and moisture of the whole plant. Sweet sorghum stalks are typically harvested manually using hand cutters or by specialized cane harvesters that cut the stalk near the ground.
Immediate Post-Harvest Handling
Grain harvested above the safe storage moisture of 13% to 14% must undergo mechanical drying and cooling. High-moisture grain in a holding bin can mold and heat rapidly, making prompt drying essential. For grain preservation, forced air is used to dry the kernels, and aeration fans cool the grain to about 50°F for long-term storage.
Forage sorghum intended for silage must be immediately chopped, transported, and packed tightly into a silo or bunker. This compaction creates an anaerobic environment necessary to initiate fermentation, which preserves feed value and prevents mold growth.
Sweet sorghum stalks must be processed into juice quickly after cutting, ideally within 24 to 48 hours. Stalks left exposed too long will see rapid deterioration and inversion of sugars, lowering the quality and yield of the final syrup. Once extracted, the juice is immediately boiled down to the desired syrup consistency.