Photo Credit
Pixabay
Botanical Name
Cosmos bipinnatus
Plant Type
Sun Exposure
Soil pH
Special Features
Subhead
Easy-to-grow annuals that thrive in poor soil and bloom from summer to fall.
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Planting
The soil should be well-draining, but other than that, 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 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’re 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—no more than 1/4-inch deep.
- Thin to 12–18 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 North Carolina Extension, “Be cautious not to overwater your plants. That and over-fertilizing can lead to the plant producing fewer flowers.”
- 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.
Types
- ‘Picotee’ has pretty white flowers with a crimson border around the edge of the flower (some are also flecked in crimson).
- ‘Sea Shells’ have white, pink, or red tube-shaped petals.
- ‘Purity’ is a beautiful, classic, white flower that looks spectacular growing against the dark-maroon ‘Niger’ hollyhock or purple basil.
- ‘Cosmos Sonata Series’ looks especially good with Bells of Ireland.
- ‘Chocolate’ cosmos adds distinction to a white campanula, dianthus, or ‘Moonshine’ achillea.
- Tall cosmos are best for the back of the garden and filling in mixed borders among perennials such as foxgloves, phlox, delphiniums, and daisies, as well as annuals such as poppies, cleome, and asters.
- Dwarf cosmos, such as the Ladybird series, are great companions for zinnias, Johnny jump-ups, pansies, alchemilla, or dark-blue morning glory.
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’s best to pick some right when the petals have opened.
- If you cut the blossoms when they first open, they’ll last more than a week in water. Strip off the lower leaves and put them in a vase.
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Cosmos can't get too much sun. They are sun-loving annuals and enjoy 8 to 10 hours of direct sunlight. The usual problem is overwatering. Water them very sparingly. Basically, cosmos thrive on neglect! Only water when the foliage starts to wilt. They are drought-tolerant.
CAN COSMOS BE PINCHED OUT WHEN YOUNG TO PROMOTE BUSHIER SHORTER PLANTS
For cosmos, pinching promotes more blooming. Deadhead spent flowers. When they are getting older with lots of seed pods, cut the plants back to 12 - 18 inches high.
How much water should i give my Cosmos everyday ?
Water only when the soil is dry and when the plants look like they need some water. Cosmos plants don't like to be wet.
I have two small greenhouse kits with white cosmos I planted them a week ago and now have a dozen sprouts around 2-3 in. tall with two leefs a piece they look good but I'm finding mold is starting to grow in the moist soil should I move them to pots already or maybe leave the lids off I'm at a loss any help would be Much appreciated~arkansas
Remove the lids and let the soil dry a bit. Air circulation will also help. The mold is not going to hurt your seedlings and may disappear with drier conditions.
I've just heard that aphids will kill my cosmos and I am scared of bugs and I live in a city with lots of sun and I want to plant cosmos but I don't know where to plant it without it having aphids. I can plant it indoors(I have a sunny window),outside, or in my green house please help!
First: if you're growing plants, you are going to encounter bugs. Before you even spot aphids, spray your plants every couple days with a few stiff sprays of water. If/once you spot aphids, just spray with insecticidal soap (soapy water) on all sides of the leaves. This should work with minor infestations before it gets out of hand. You can always resort to chemicals, but staying on top of the issue is best for you. Finally, if you notice aphids, release tons of ladybugs, our sweet beneficial insect which lives on...eating aphids! Now, ladybugs are "bugs," too. :-) In a greenhouse, they are aphid-eating machines.
Thanks that help me a lot I'm just scared of most bugs that don't seem friendly and also do all cosmos get aphids?cause if some don't that'll be much easier and are they harmful to humans?
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