The white, pink, or rose flowers of this annual cosmos native to Mexico are a welcome addition to the garden along with its fine fern-like foliage. They are easy to grow from seed, require little care, do well in lean soil, and tolerate drought when once established. Cosmos are cross-pollinated by insects so grow only one variety at a time if you plan to collect seeds for future years. Dark color and the blotch at the base of the petals of some varieties are dominant traits when crosses are made. The yellow, orange, or red flowered Klondike cosmos (Cosmos sulphureus), however, does not cross with C. bipinnatus so you can grow them together without fear of mixing the two different species.
Seeds can be sown outdoors after the last frost. Seeds can be sown in flats indoors for earlier bloom no more than four weeks before the last frost. Seedlings grown in containers more than four weeks are likely to get to tall to transplant successfully.
1. Sow seeds by pressing them into the soil. Do not cover as the seeds need light for germination.
2. Provide temperatures between 70 to 75 F and keep moist but not wet. Seeds should germinate in three to ten days under optimal conditions.
3. Transplant into individual pots when seedlings have two or more true leaves.
4. Plant in garden eight to ten inches apart for small varieties and eighteen to thirty six inches apart for tall varieties.