Cosmos are annuals, grown for their showy flowers. The flowerheads may be bowl– or open cup–shaped 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 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 ¼-inch deep and 12–18 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.
- They can tolerate warm, dry weather.
- Depending on the type of flower, cosmos can grow anywhere between 18–60 inches tall.
- 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.
- In order to prolong flowering, you should deadhead the plants (remove the dead/faded flowers).
- Because some of these plants can grow really tall, staking may be necessary.
- Water regularly, but make sure you don't over-water the plants. Over-watering and over-fertilization can lead to plants with fewer flowers.
- Cosmos beds may become weedy due to the fact that they self-seed, so remember to check them.
- To harvest more seeds, remember to leave a few flowers on the plant because they will self-seed.
- You can cut the flowers off anytime after blooming, but it's best to pick some right when the petals have opened.
- If you cut the blossoms on good stems when they first open, they'll last more than a week in water.