The cotton plant belongs to the Malvaceae family, which also includes plants like hibiscus and okra. It is commercially grown as an annual shrub for the soft, staple fiber that surrounds the seeds. Successful production relies on the precise development of specialized reproductive structures. This progression from a simple bud to the final lint-filled structure is a genetically programmed sequence.
Initiation: From Vegetative Growth to Squaring
The first visible step in the plant’s reproductive journey is the formation of the “square,” which is the small, triangular flower bud. This transition typically begins around five to seven weeks after planting, marking the shift from purely vegetative growth to fruiting development. The plant develops two types of branches: vegetative branches that produce leaves and support growth, and fruiting branches, which grow in a zigzag pattern and bear the squares.
The square is enclosed and protected by three triangular leaf-like structures called bracts. Inside this enclosure, the flower’s reproductive parts develop over approximately three weeks before blooming. The appearance of the first squares sets the stage for the plant’s potential yield.
Anthesis: The Cotton Flower in Bloom
The culmination of the squaring phase is anthesis, the brief period when the cotton flower fully opens. This event usually occurs about 21 days after the square first appears. The short duration of the open flower is a defining characteristic of this stage, as it typically lasts for only a single day.
When the flower first opens, usually in the morning, the petals are a creamy white or pale yellow color. Self-pollination and fertilization must occur within this short window to ensure the formation of the fruit. By the next day, the flower changes color, turning pink or red before withering and dropping off, leaving behind the newly fertilized ovary.
Fructification: Boll Development and Maturation
Following the fertilization of the flower, the developing ovary transforms into a closed, green structure known as the boll. This stage is when the actual cotton fiber is created and requires 50 to 70 days to mature. The boll is sensitive to environmental factors like temperature, water availability, and nutrient status throughout its development.
Fiber development within the boll proceeds through three distinct, overlapping phases. The first is the fiber elongation phase, which begins immediately after fertilization and lasts for about three weeks. During this time, the fiber cells, which originate from the seed coat, rapidly lengthen to establish the final staple length. The fibers exist as thin-walled, hollow tubular structures during this initial growth period.
The second phase is the secondary wall thickening, or filling phase, which begins around the fourth week after flowering, once elongation ceases. This phase involves the deposition of cellulose inside the hollow fiber tube. This cellulose deposition provides the fiber with its structural strength and maturity.
The final phase is maturation, where the boll reaches its maximum size, and the fiber and seed physiologically prepare for opening. Throughout these stages, the developing bolls become the primary “sink” for the plant’s energy, drawing carbohydrates and nutrients away from new vegetative growth. This intense demand makes the boll vulnerable to shedding if the plant experiences stress from drought, temperature extremes, or nutrient deficiencies, particularly potassium.
Senescence and Harvest Readiness: The Open Boll
The final phase is marked by senescence, the natural aging and decline of the plant. This signals the end of the fruiting period and triggers boll dehiscence, the splitting open of the hardened fruit capsule. As the green boll dries, its outer casing turns brown and splits along its seams, typically into three to five segments.
The splitting action exposes the fluffy, mature cotton fiber, which has fully dried and fluffed out of the locks. The opening of the boll indicates that the fiber is physiologically mature and has reached its final quality characteristics. At this point, the cotton is ready for mechanical or manual picking, concluding the field phase of production.