Cosmos is one of the easiest flowering annuals for a gardener to plant, despite their experience. In fact, caring for it too much, will actually cause the seeds not sprout, or result in spindly plants with few blooms. Cosmos belongs to the family Compositae, with 20 known species. If your garden can use a hardy, drought tolerant, flowering plant bursting in a vast array of colors ranging from orange, pinks, whites, yellow and stripes, try planting cosmos.
Delay planting the cosmos seeds into the ground, until conditions of winter has left your area. Depending on the species you are growing, cosmos germinates best in temperatures ranging from 65 to 80 degrees. Planting the seeds in a cooler season lowers the chance of germination.
Select a planting site that receives full sunshine throughout most of the day. Cosmo will be tall, lanky and the flower production will be low to none, if planted in the shade. Cosmos will grow best in full sun.
Plant the seeds in sandy soil that drains well. The addition of compost is not required. Adding it will actually cause the plants to produce fewer flowers and more vegetation. Cosmos thrive in poor soil conditions. Heavy soils such as clay will need amending with sand, to create better drainage.
Weed the planting area, removing any grass or unwanted vegetation. The seeds will have a better chance of sprouting without competition. If the area was cleared using herbicide, delay the planting of the cosmos seeds for up to 2 weeks. Planting too soon in a treated area can prohibit the seeds from germinating.
Scatter the cosmos seeds where you desire them to grow. Single placement of the seeds is not required when planting cosmos. Cover the seeds with a very fine layer of soil. Planting the seed too deep will cause them not to sprout.
Water the area. Keep the planting area lightly moist until the seeds germinate in 7 to 21 days. The length of germination will depend on the variety you are growing. Once established, cosmos are relatively drought tolerant and will require water only once per week.