During the 21-day period from square to bloom, there are several recognized developmental stages of the cotton flower bud. A “pinhead” square is the first stage at which the square can be identified. The next stage of square growth is “match-head” or “one-third grown” square. Just prior to the time the flower opens, a candle shape can be seen. This period of square development prior to bloom is called “squaring.”
Once the cotton begins to bloom, it is said to be “flowering.” A cotton plant typically blooms or flowers for about 6 weeks. Thus, until the cotton begins to produce fruit, the stage of development is discussed in terms of leaves or nodes. Once fruiting begins, the stage of cotton development is discussed in terms of square development and the number of nodes. Once blooms are present, the stage of cotton development is discussed in terms of weeks of bloom.
Figure 1. Development of the bud from match head square (a) to flower (e) involves both a size increase and petal development. Two bracts have been removed from each square, candle and bloom to show this development.
The Cotton Flower
As discussed previously, the cotton square is actually a flower bud. The first visible structures of the square are the leaf-like bracts, or epicalyx. Three bracts surround the flower bud in a pyramid-like shape. The cotton plant produces perfect flowers, meaning the flower contains both male and female organs. The first square is typically visible on node 5 to 7 about 35 days after planting. Anthesis, or a flower bloom, occurs approximately 21 days after the first square appears.
When a pollen grain reaches the stigma, it germinates into a pollen tube. The pollen tube grows through the style, the micropyle, and into the ovule chamber, where fertilization takes place. Anything that reduces egg or pollen viability or tube growth in a flower adversely affects the final yield for that boll.
Figure 2. Parts of a mature cotton flower. The cotton flower contains both male and female parts.
Stages of Flowering
Flowering is important to cotton production because pollinated flowers form cotton bolls. The bloom process takes several days, and bloom age can be estimated by the bloom characteristics. On the day a flower opens it is white in color. Pollination of that flower usually occurs within a few hours after the white flower opens.
On the second day the flower will have a pink-like color, and a red color on the third day. Approximately 5 to 7 days after a flower appears it usually dries and falls from the plant exposing the developing boll. Occasionally a flower will stay attached to the developing boll for a longer period of time. This is referred to as a bloom tag.
Figure 3. Development of a cotton bloom. A white flower emerges on day 1 (a), then gradually darkens and takes on a red color during days 2, 3 and 4 after emergence (b and c). The bloom eventually dries up and either falls off or becomes a bloom tag (d).
Cotton Growth and Development Stages
Cotton Squares to BloomCotton Growth and Development Publication - Univ. of Georgia