Cotton’s journey from a field crop to a usable fiber is a highly industrialized, multi-step process. Modern harvesting relies heavily on specialized machinery to manage large fields efficiently. The timing of this harvest is crucial, generally occurring in the United States from late July in the southernmost regions through November in cooler areas. This precise window ensures the fiber reaches its maximum quality before weather events, such as rain or frost, can cause damage.
Preparing the Crop for Harvest
Before machinery enters the field, the cotton plant undergoes chemical preparation using harvest aids to maximize fiber quality and harvesting efficiency. The removal of leaves is necessary because green plant material contains chlorophyll, which can severely stain the white cotton lint during mechanical picking.
Defoliation is the process of chemically inducing a natural leaf drop, where defoliants accelerate the process without dehydrating the leaf tissue. Desiccation, by contrast, uses chemicals to rapidly dry out and kill the leaves and plant tissue. Boll openers, which release the plant hormone ethylene, are often applied with defoliants to ensure a high percentage of cotton bolls are fully open and ready for a single pass harvest.
Mechanical Harvesting Methods
The actual process of picking cotton from the stalk is handled by two distinct types of mechanical harvesters: the spindle picker and the stripper harvester. The choice between these two machines depends on the cotton variety, the local climate, and the expected yield of the field. Both machines automate a task that was historically slow and labor-intensive, but they operate using entirely different mechanical principles.
Spindle Pickers
Spindle pickers are selective harvesters designed to remove only the lint from the open cotton boll. They use hundreds of rapidly revolving, barbed spindles that rotate and twist into the open bolls. The barbs grip the cotton fibers, wrapping the lint around the spindle while leaving the burr and the rest of the plant structure intact. A specialized component called a doffer then removes the collected cotton from the spindle. Spindle pickers are used in high-yield areas with longer-staple, less storm-resistant cotton varieties, such as the Mid-South and Southeast United States. Because they are selective, they collect minimal foreign plant material, leading to a cleaner initial sample of seed cotton.
Stripper Harvesters
Stripper harvesters, conversely, are nonselective machines that remove the entire boll and a significant amount of associated plant material from the stalk. They use specialized brushes or rollers to physically strip the bolls, leaves, and stems off the plant. This method is favored in drier regions, such as the Texas High Plains, and is used on storm-tolerant cotton varieties where the lint is held tightly within the burr. Although stripper harvesters operate faster and cost less to own than spindle pickers, the harvested material contains considerably more trash. This means the cotton requires more intensive cleaning at the ginning facility to separate the lint from the unwanted material. For stripper harvest to be effective, the plants must be fully desiccated to prevent green plant matter from contaminating the fiber.
Field Processing and Storage
Once harvested, the cotton is immediately compressed into large, dense units known as modules for temporary storage and transport. This step is a necessary logistical solution, as the harvesting rate of the machines is much faster than the processing rate of the cotton gins. The seed cotton is unloaded into a specialized machine called a module builder, which compacts the cotton using a hydraulic ram. The resulting modules are tightly packed units, often cylindrical with an integrated plastic wrap. This compaction allows the cotton to be safely stored at the edge of the field, protecting it from weather damage and facilitating transport to the gin.