How to Grow Cosmos Sulphureus

Choose a site that features good drainage in which to grow Cosmos sulphureus. If necessary, Cosmos sulphureus tolerates dry soil. Select a site that receives plenty of sunshine.

Plant Cosmos sulphureus in soil of medium or even poor quality. This flower has little trouble growing in less-than-ideal soils. It actually grows too well if you place it in a rich, fertile portion of the landscape. It will grow too large, making it susceptible to wind and gravity. Stake the larger plants if you do put them in a fertile site so they do not droop over due to their weak stems.

Start the seeds of Cosmos sulphureus indoors in containers about four to six weeks prior to the last expected date of a spring frost. Transplant them outside after any threat of a frost passes, advises Cornell University. Plant the seeds in your garden just before the last frost date if you wish to avoid having to transplant Cosmos sulphureus.

Remove any spent flowers on Cosmos sulphureus to prevent this annual from self-seeding. Orange cosmos generates large amounts of seeds, making it a potentially aggressive flower, notes the Missouri Botanical Garden. By removing the spent flower heads, you not only stop the plant from producing seeds, you encourage further blooming. Harvest the seeds in autumn if you wish to use them for planting the following spring.

Avoid having to stake your orange cosmos by selecting some of the dwarf cultivars for your landscape. Choose types such as Sunny Gold, which grows 12 inches tall, or Ladybird, a cultivar that matures between 12 and 18 inches high.