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Planting, Growing, and Caring for Cosmos
Planting
The soil should be well-draining, but other than that, cosmos don鈥檛 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 blooms. Cosmos are also tolerant of most soil pH levels but grow best in neutral to alkaline soils (pH of 7.0-7.5).
Cosmos can tolerate warm, dry weather very well. They are even drought-tolerant.
When to Plant Cosmos
- Direct-sow seeds outdoors once the danger of frost has passed.
- Alternatively, sow seeds indoors 4 to 6 weeks before your last spring frost date in trays or pots with a good seed-starting mixture. Move them into 5-inch pots as soon as they鈥檙e 3 or 4 inches tall.
- Young plants (transplants) can be planted outdoors once the danger of frost has passed.
How to Plant Cosmos
- Just sow seeds lightly鈥攏o more than 1/4-inch deep.
- Thin to 12鈥18 inches apart when seedlings are a few inches tall. Depending on the variety, cosmos can grow anywhere from 18 to 60 inches tall, so plan accordingly.
- If you are growing cosmos from seeds, be mindful that it takes about 7 weeks to first bloom. After that, your flowers should continue to bloom until the first fall frost.
- If you let the spiky-brown seed heads blow away during the fall, cosmos are likely to self-sow throughout your garden.
Growing
- To prolong flowering, you should deadhead the plants (prune off dead/faded flowers). This speeds up flower development and aids branching.
- Because some of these plants can grow really tall, staking may be necessary. Offer them protection from strong winds, encourage balanced branching by pinching out (aka pruning) central shoots or stem tips, or stake them. Growing them against a fence can also provide the necessary support.
- Water regularly until plants are established or if it is unusually dry. According to the , 鈥淏e cautious not to overwater your plants. That and over-fertilizing can lead to the plant producing fewer flowers.鈥
- Cosmos can tolerate dry soil, even in a hot, arid, sunbaked spot.
- Cosmos beds may become weedy due to the fact that they self-seed, so remember to remove flowers before they go to seed or to thin seedlings in the spring.
Harvesting
Harvesting Seeds and Cut Flowers
- 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鈥檚 best to pick some right when the petals have opened.
- If you cut the blossoms when they first open, they鈥檒l last more than a week in water. Strip off the lower leaves and put them in a vase.
Catherine Boeckmann
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How nice of your friend! You can still sow the seed in the spring of 2017, but it might germinate poorly. Be sure to store the seeds in a cool, dry place, and don’t be disappointed if the cosmos are not as healthy and vibrant as expected. For the best germination, you would probably want to buy newer seed.
Hi!
I'm growing cosmos from seedlings in a pot and I have read that I am supposed to pinch them. Is this true? If so when am I'm supposed to do this, and how? I am in Inglewood CA. Thanks for any help. Love this site!
A little light pinching on young plants (and more on established plants) is a good idea, as it encourages bushier growth/more branching at the base resulting in more bloom potential. To pinch, remove the growing tip of the plant.
I just recently purchased some White Cosmos Flowers from my local plant nursery/garden center. Considering that I live in Tucson, AZ and how hot it is outside, how often should I fertilize the flowers and how often do they need watering? We in Tucson are getting ready for the monsoon season. By the way, your site and information are astounding and I love it! Thank you and Many Blessings!
I water my cosmos every other day. On a very hot day I give mine a drink in the evening
I planted Cosmos seeds in small pots inside(to start them out) but packet does not say how often to water. Also, I live in Phx, AZ. Any special instructions for their health in 'hell'? That's how hot it can get here.
Cosmos flowers love the heat and are drought tolerant. Keep the soil moist in the pots but do not overwater. Sow some seeds in the soil outdoors. Cosmos seedlings are known to grow quickly from direct-sown seed.
I want to plant indoor flowers plants.pls suggest some plants for this winter.
Some indoor flowers that like the darker days of winter are African violets, winter begonia, kalanchoe, cyclamen, and many bulbs that you can force to bloom.
I want to know may I plant the plant of cosmos now?
