Cosmos Seeds - Treasuresbylee - Black Cosmos Seeds - 30 Heirloom Flower Seeds Black 30 Freshly Harvested Seeds Beautiful Packaging, Instructions on backside. Cosmos are annuals, grown for their showy flowers. The flowerheads may be bowl or open cupshaped and are atop of long stems. Cosmos are easy to grow and make good border or container plants. They make for good decorations in flower arrangements and also attract birds, bees, and butterflies to your garden. If you are growing cosmos from seeds, be mindful that it takes about 7 weeks to first bloom. 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. Seedlings grow fast, so move them into 5-inch pots as soon as they're 3 or 4 inches tall. Plant seeds in moist, well-drained soil about 1/4-inch deep and 1218 inches apart after the danger of frost has passed. You can also plant transplants instead of seeds. They also like soil that is not too rich.