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Cosmic cosmos!

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Once you learn how to grow cosmos, a favourite annual for summer garden colour, and realise just quite how easy it is, you’ll be adding them all over your garden. 

The pollen-rich flowers are a favourite of bees and other pollinators and are excellent for companion planting alongside vegetable and fruit crops in a kitchen garden, too, as they entice pest predators and valuable pollinators. 

Cosmos plants (Cosmos bipinnatus) reach varying heights in roughly 20 colours, adding frilly texture to the flower bed.

Growing cosmos is simple and cosmos flower care is easy as well as rewarding when single or double blooms appear on stems reaching from one to four feet. Cosmos plants may be featured at the back of a descending garden or in the middle of an island garden. 

Planting cosmos flowers results in many uses of the specimen, such as cut flowers for the indoor display and backgrounds for other plants. Cosmos can even be used as screens to hide unsightly elements in the landscape. 

How to grow cosmos 

When planting cosmos flowers, locate them in soil that has not been heavily worked.  Sunny, dry conditions, along with poor to average soil, are optimum conditions for growing cosmos. Cosmos plants are usually grown from seed. Scatter seeds of the cosmos onto a bare area in the location where you wish to have them grow. 

Once planted, this annual flower self-seeds and will provide more cosmos flowers in the area for years to come. Daisy-like flowers of the cosmos plant appear atop tall stems with lacy foliage. Cosmos flower care can include the deadheading of flowers as they appear. This practice forces growth lower on the flower stem and results in a stronger plant with more flowers. Cosmos flower care can include cutting flowers for indoor use, achieving the same effect on the growing cosmos plant.

Because some of these plants can grow tall, staking may be necessary. Offer them protection from strong winds, encourage balanced branching by pinching out central shoots or stem tips, or stake them. 

Water regularly until plants are established or if it is unusually dry. Make sure you don’t over-water cosmos; over-watering and over-fertilization can lead to plants with fewer flowers. Cosmos can tolerate dry soil, even in a hot, arid, sunbaked spot.

Cosmos beds may become weedy because they self-seed, so remember to remove flowers before they go to seed or to thin seedlings in the spring.


Q & A on cosmos

Do cosmos come back every year? 

Nearly all cosmos are annuals meaning they do not come back every year. In order to have blooms every year, you will need to resow the seeds the following spring. 

The only exception to this rule is chocolate cosmos, Cosmos atrosanguineus, which is grown like a dahlia from a tuber and is a perennial. Chocolate cosmos is loved for its delicious vanillary-chocolate scent and velvety brown flowers, and since it is a perennial, will come back year after year. 

Annual cosmos can also self seed. If you let some of your cosmos flowers die naturally and fall to the ground, they will germinate seeds by themselves.

Where do cosmos grow best?

They like full sun and do not like windy conditions. Space plants approximately two feet apart; with tall cosmos, space plants closer than the recommended two feet and let them support each other. Both germination and growth are fast, but cosmos plants are frost tender, so don’t be in a rush and wait until perhaps May.

Will they survive winter?

Cosmos are not hardy plants and if you leave them in your borders over winter there is a real chance they will be killed by a sharp frost, or rot in cold wet soil.

When deadheading, cut the stem back to the first leaf beneath the flowerhead. The perennial chocolate cosmos varieties will need winter protection. Place them in pots until they’ve finished flowering, then shelter over winter in a frost-free place until spring.

Can you put cosmos in hanging baskets?

Tucked into a hanging basket or container, cosmos create a vibrant and showy display. A butterfly attractant, they also attract the winged insects to the garden to drink the sweet nectar. Cosmos flowers prefer full sun only and well-drained, nutrient rich soil.

Should you pinch cosmos flowers? 

You should pinch out the growing tips of cosmos to encourage branching and flowering, and in around 12 weeks you should see your first blooms.

If you then want to enjoy those flowers in the house as well as in the garden, cosmos make excellent cut flowers. To harvest for cut flowers, cut the cosmos blooms when they are beginning to unfurl in the morning as this is when there will be the most moisture making them less likely to wilt.

Plunge the blooms into a bucket of warm water, stripping off lower leaves to avoid them in the water. Re-cut the stems regularly and refresh the water and they should last up to ten days in the vase.

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