SUNFLOWERS and its stages of development

April 2019

Jenny Mathews, Pula Imvula contributor. Send an email to jenjonmat@gmail.com

It has been another abnormal season in the summer cropping regions of the country. The late rains saw many farmers only planting their sunflower crops late in January and even into early February.

While the sunflower plant can be very forgiving in that it is quite hardy to those early light frosts, this season will see many farmers holding their breath and hoping for maximum potential yields before the cold weather sets in!

The total amount of time necessary for a sunflower plant to grow to maturity is dependent on both its genetic make-up and the environment it is growing in. A sunflower’s leaves are phototropic which means they follow the sun and it is believed this increases the plants use of light for photosynthesis. 

Sunflowers are known as composite flowers. Although the large flower head at the top of the plant is often thought to be the flower, it is in fact hundreds of small flowers. The male (stamen) and female (stigma) are both present in disk flowers. The stamen is composed of filament and pollen-producing anthers. The stigma houses the style, which receives the pollen and allows it to travel down to the ovary, where the unfertilised seeds, i.e. the ovules, are located. This process of pollination enables the flowers to produce seeds. 

The yellow petals on the outer circle of the sunflower head are in fact not petals but each is an individual ‘ray flower’. Ray flowers serve to attract pollinators to the ‘disk flowers’. The disk flowers are those tiny buds in the middle of the sunflower head (Figure 1).

Broadly speaking a sunflower requires about eleven days from planting to emergence; then 33 days from emergence to formation of the ‘sunflower head’. 27 days later the first anther will appear, and the last anther will form about eight days later. It will take about another 30 days from the appearance of the last anther to maturity. (The anther is the pollen producing part of the sunflower). 

It is helpful for farmers to understand the growth stages of the plant and its needs at different stages. Every cultivar in the market has an indication of the number of days to maturity. In a late season like this one, many farmers would have selected a shorter growing cultivar

CONCLUSION
Understanding the different stages of development is important. It is the farmer’s responsibility to monitor his fields throughout the growing season to ensure that every plant is given the opportunity to develop to its full potential. Some factors like absence of rain cannot be controlled but the addition of nutrients into the soil and the control of pests and diseases are aspects that can be managed. The moment a plant is setback by any problem, the leaves will wither prematurely, and yields will be negatively impacted. 

REFERENCES
Schneiter, A.A., and J.F. Miller. 1981. Description of Sunflower Growth Stages. Crop Sci. 21:901-903. Reviewed and reprinted May 2013. Available online: https://www.ag.ndsu.edu/publications/crops/stages-of-sunflower-development
Sunflower growth stages Available online: https://cereals.ahdb.org.uk/media/184824/sf2_growth_stages.pdf
Sunflower production – A Concise Guide. Available online: https://www.kzndard.gov.za/images/Documents/RESOURCE_CENTRE/GUIDELINE_DOCUMENTS/PRODUCTION_GUIDELINES/Look-n-Do/Sunflower%20Production.pdf

Publication: April 2019

Section: Pula/Imvula