Cotton has a complex plant structure, which can make it a very challenging crop to understand and manage throughout the growing season.
Cotton plants follow a set pattern of growth according to accumulated heat units (DD60s); however, sensitivity to varying environmental conditions can affect development.
Understanding cotton growth and development can help build a foundation for proper crop management.
Calculating Heat Units
Cotton growth stages may be calculated by the number of days after emergence, or more accurately, by the number of heat units accumulated. In cotton, little to no development occurs below 60° F, so to calculate heat units (DD60s), add the maximum and minimum temperatures for the day, divide by 2 (to find the average), and subtract this number by 60. Total accumulation of DD60s can help determine the growth stage of a cotton crop (Table 1).1
Table 1. Cotton growth stages indicated by the accumulation of days and DD60s.
Emergence and Stand Establishment
Emergence typically occurs 4 to 14 days after planting, or after the accumulation of 50 DD60s.2Seedling establishment is complete once the cotyledons emerge through the soil and unfold to expose the epicotyls and apical meristem (Figure 1).
To help optimize cotton stand establishment, consider the following:
Seed quality (germination test results of at least 80%).
Favorable degree-day forecast for 5 days post planting with expected heat unit accumulation of approximately 25-50 DD60s.
Soil at planting depth should be warm and moist. By mid-morning, the soil temperature should be at least 68° F at the desired planting depth for 3 consecutive days.3
Seed should be planted 0.5 to 1.5 inches deep depending on the soil texture and moisture. For coarse soils, seed should be planted in moisture. Shallow planting can result in poor seed-to-soil contact and deep planting can delay emergence and cause skippy stands. Confirm depth by digging up seeds after planting 50 to 100 ft of row.
Early Vegetative Growth
Vegetative growth includes development categorized by leaves or nodes. Cotton has an indeterminate growth habit allowing plants to grow very tall and heavy with vegetation if not managed.
1st true leaf. Emerges about 50 DD60s (or in 3 to 7 days) after seedling establishment, shifting the plant’s energy source from cotyledons to 1st leaf emerging.
Main stem leaves. The first structures to appear on the main stem.
Nodes. Points of attachment where leaves and branches form (Figure 2). A new node is produced by the apical meristem an average of every 3 days.
Leaves. Leaves produced from the main stem are called main stem leaves and leaves located on fruiting branches are called subtending leaves.
Cotton plants develop 2 types of branches: vegetative and fruiting.
Vegetative branches. Straight growing branches with the main purpose of producing energy through photosynthesis. Mainstem and other vegetative branches typically form on lower nodes.
Fruiting branches. Branches that grow in a zigzag pattern and contain multiple meristems and form fruiting buds. The first fruiting branch will typically form at mainstem node 5 or 6. New fruiting branches develop about every 3 days and squares form at new positions on fruiting branches every 6 days.
Reproductive growth is characterized by square development and node location on the plant.
Square development. The square (pre-bloom flower bud) forms at the initiation of a fruiting branch.
First square position. This is the location where the first square is produced. As a square develops, the section of the branch between the main stem and square elongates and an auxiliary meristem also develops on the branch adjacent to the square. The auxiliary meristem will produce a second position square and a subtending leaf. The first square typically forms on nodes 5 to 7.
Cotton bud formation. It takes 3 to 4 weeks from square until bloom. There are several development stages of a cotton bud (Figure 3).
Pinhead square (a). The first stage the square can be identified.
Match-head square (b). When the bud is about 1/3 grown.
Candle (d). Just prior to bloom, and shaped like a candle.
White bloom (e). Once the bud blooms. The flowering period typically lasts 4 to 6 weeks.
Bloom growth continues reproductive development and is characterized in terms of weeks of bloom (Figure 4). When a bloom first opens, the flower is white and pollination may occur within hours of opening. By Day 2, the flower will have a pink tint and turn red by Day 3. The flower will dry up and fall off the plant between Days 5-7, exposing a fertilized boll. During early-bloom, the mainstem will continue to grow and add new leaves, nodes, and squares. As more bolls are set, the plant’s energy is diverted from vegetative growth to the boll formation.
Nodes above white flower (NAWF). During flowering, cotton plant development may also be categorized in terms of NAWF This measurement is taken by the number of nodes separating the uppermost first position bloom and the terminal of the plant. At first bloom there may be 9 or 10 NAWF, and the number decreases as blooms continue to form up the plant. Flower development will eventually slow and cutout occurs at 4 or 5 NAWF when no more harvestable fruit is set on the plant.
Under optimum conditions a boll requires about 50 days to open. The fibers are very sensitive to environmental conditions during boll development. The 3 phases of boll development are as follows:
Enlargement. The fibers produced on the seed begin to elongate and the maximum volume of the boll and seeds are set. The fibers during this stage are a thin-walled tubular structure. This phase typically lasts 3 weeks.
Filling. The filling phase begins during the 4th week after flowering. The secondary walls of the cotton fiber will form, a process also known as deposition. This phase continues for 2 weeks.
Maturation. This phase begins when the boll reaches full size and maximum weight. The fiber and seeds within the boll mature and boll dehiscence occurs. The walls of the boll dry and split, opening the boll.
1Advancing Cotton Education. Growth and development of a cotton plant. National Cotton Council and The Cotton Foundation. http://www.cotton.org/.
2Ritchie, G.L., Bednarz, C.W., Jost, P.H., and Brown, S.M. 2007. Cotton growth and development. The University of Georgia Cooperative Extension Service. Bulletin 1252.
3Main, C. L. 2012. Cotton production in Tennessee. University of Tennessee Extension. W288. http://www.utcrops.com/.
Web sources verified 03/01/16. 120918013703