Bloom Time Summer, Fall
Cosmos grow in both beds and containers

Just sow seeds lightly—about ¼-inch deep and 12–18 inches apart after the danger of frost has passed. You can also plant transplants instead of seeds.

Cosmos don’t need any special soil preparation. In fact, they like soil that is not too rich, as rich soil will encourage foliage at the expense of bloom.

If you are growing cosmos from seeds, be mindful that it takes about 7 weeks to first bloom. After that, though, your flowers should continue to bloom until the next frost.

If you want a head start, you can plant cosmos indoors 4 to 6 weeks before the last spring frost in trays or pots with a good seed-starting mixture. Move them into 5-inch pots as soon as they’re 3 or 4 inches tall.

https://www.almanac.com/plant/cosmos#