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About the Author & Content Disclaimer
The advice in this post is based on 10+ years of hands-on experience testing seeds in our sandy Suffolk Garden.
While I love sharing my journey and the things I discover, please understand that I am not a certified professional in gardening or wildlife. I ground my content by deep-diving into reliable books and expert resources, but please use my advice only as a guide for your specific garden.
I use and sell the same UK-sourced, wildlife-approved seeds in my own garden that you see throughout this site. Shop the seeds here.
If you notice any inaccuracies or have additional insights to share, please feel free to contact me via this website's contact forms.
Cosmos became a delightful addition to my garden in 2023. Drawn by their reputation for attracting pollinators, I started with a packet from Sarah Raven's website. While, a smaller variety also emerged from my existing prairie seed mix. I was captivated first by the feathery foliage, and then utterly charmed by the blooms that drew a constant buzz of happy pollinators, including the humble bumble bee. Needless to say, Cosmos have become an indispensable part of my garden and I'm glad to say they are usually the last blooming flower standing as we approach December.
This guide provides comprehensive information on cultivating cosmos in British gardens, from sowing seeds to achieving a vibrant floral display.
Cosmos are renowned for their sun-worshipping nature and extended flowering season, stretching form May to October. These vibrant blooms, ranging from pristine white to captivating shades of pink, red, and orange, in pastels or deeper shades of colour with delightful feathery foliage. Shorter varieties enhance container displays, while all cosmos varieties excel as cut flowers. Their simple, open form guarantees to illuminate any garden throughout autumn, attracting a multitude of pollinators.
To cultivate flourishing cosmos, opt for moist yet well-drained soil in a location bathed in full sun. Regular deadheading extends the flowering period. Seeds can be saved from spent blooms for subsequent seasons.
Originating from Central and South America, cosmos thrive in warm, sunny areas with free-draining soil. As they do so well in dry sunny areas, we added them to our prairie mix with is drought tolerant.
Cosmos seeds can be sown directly into the designated growing area in early spring, or alternatively, sown indoors in small pots or modules filled with free-draining seed compost. For pot-grown seedlings, transplanting occurs in late May, once the risk of frost has subsided.
Potting on from seedling trays
Here I am potting on my seedlings, although I'm happy to put seeds directly into the ground as well.
Once seedlings establish 2-3 pairs of leaves, consider pinching out the growing tips to promote bushier growth and enhance flower production. Taller varieties may necessitate staking for support. Regular deadheading and application of liquid fertiliser throughout the flowering period will encourage a continuous display. When deadheading, prune the stem back to the first leaf located beneath the flower head.
Pinching out the top leaves to create a busher plant
Seeds from flowering cosmos can be collected and stored for planting the following year.
Cosmos are generally trouble-free to cultivate, with the exception of potential threats from slugs and snails during the seedling stage when the plants are young and vulnerable.
Excessively tall, strong, and bushy cosmos plants without blooms might be attributed to overfeeding with nitrogen-rich fertiliser or overly fertile soil. This can stimulate excessive foliage growth at the expense of flower production. Cosmos thrive in full sun and well-drained, average garden soil. Shade-grown plants will also struggle to flower. Pinching out cosmos plants can encourage more blooms.
Avoid sowing cosmos seeds too early, and ensure they receive ample light to prevent leggy growth. If your cosmos seedlings become leggy, fret not. Simply prick them out and pot them on into slightly larger containers, planting them a little deeper than before. If not already implemented, pinch out the tops to promote bushier growth.
You can find a Cosmos seed mix full of pinks and whites on my online shop - Click here to purchase cosmos seed
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