Growing Cosmos Flowers
Cosmos are a classic summer flower, they are pretty, abundant and easy to grow once you get the hang of them. Three years ago I over sowed and over planted cosmos. Too much of a good thing meant the following year I did very few. In fact I direct sowed them, totally bypassing any tray sowing, and they should have started blooming in mid July. But they did not bloom, not until the days got cooler and shorter. I inadvertently taught myself a few life and flower lessons! Too much of the one flower can lead you to not appreciating them and the right amount succession sowed can make you truly appreciate them.
Cosmos seeds germinate pretty quickly but if you are overeager and sow too early you can have some very leggy plants that are probably best composted. First year I sowed cosmos I sowed them very early February and they did indeed end up in the compost heap. I was listening to a podcast recently and they were discussing how the first few days of life after a seed’s germinates determines the health of the plant in the long term. I would feel this does indeed apply to annuals like cosmos. Now I never sow them earlier than March. Of course that’s not to say you shouldn’t experiment if you need earlier blooms for a specific reason or event, just for my growing purposes I don’t need them early as I should have biennials and hardy annuals filling the flower gap they might be needed for.
Cosmos seeds are a larger size seed and very easy to handle. You can pop them in an individual cell of a tray without worry of sowing 20 instead of one by mistake. I sow them is the months of March and April indoors in trays and direct sowing April – June outdoors. I would suggest early June to allow you some flowers in Autumn but this is of course dependent on your first frost date.
How to grow: Sow in a seed tray by placing a seed individually in a seed cell. Water 4-6 weeks before your last frost day at a temp of 18-21 degrees, a sunny windowsill will do. They can get leggy quickly so don’t sow too early. Acclimatise and plant out once danger of frost has passed. Can be also sown directly in April/May where they are to flower. Cosmos benefit from pinching and regular deadheading. They may require stalking in a windy area.
Cosmos sometimes have trouble blooming in the middle of summer, when the days are at their longest. They are said to bloom best when daylight hours are 14 or less. It is called photoperiod and it explains why my flowers just wouldn’t bloom that July! It’s more likely to affect immature plants and not mature ones so mine had been direct sown to begin flowering in mid July. This means a week or two earlier sowing could have potentially insured blooms all summer. The days to maturity of cosmos is from 60 to 90 days. This also means that there a perfect late summer flower.
Cosmos plants also can be pinched to encourage branching and they are wonderful cut and come again flowers so keep cutting and more will grow. I also experimented with transplanting thinnings of diect sown cosmos. When you direct sow its very easy to oversow seeds and have lots of little seedings pop up. After seven days of heavy rain ( I mention the rain as they roots of the seedlings were very hydrated) I thinned seedlings and moved them to the polytunnel where they thrived until November. Possibly if the roots were not as hydrated and it was a different time of year they might not have survived.
There are many varieties and colours of cosmos to grow. Lots of whites and pinks and wines! I tend to grow a mix and then some whites for events. I trialed apricot last year but found it to be very short and not as useful as I had hoped it might be! I also grow chocolate cosmos which is a tender perennial, I’ll have to do a second blog post on it.
This season I have added a classic Cosmos purity to my seed offerings, you’ll find the seeds here in the links Purity White Seeds as well as a Sensation mix Seeds
I’ll never be without Cosmos in the summer! Happy growing and they are very easy to grow once you make it easy on yourself by not sowing too early or too late.
Maria