Is anybody successful at growing cosmos?

[N0m0rerain]

Can you share your tips, it just doesn’t seem to grow well for me .

I grew loads last year! I thought I'd done something wrong as they took forever to germinate, were either leggy or stumpy, and then didn't actually bloom until very late summer/early August. Then I had loads of beautiful flowers until the first frost.

Other than being patient with them, I didn't do anything special. They survived being overwatered when seedlings, being transplanted from the propagator to pots too earlyz and also being left outside in the rain for a week when I was hardening them off and forgot about them!

I've got some seeds on order, so I'm looking for tips too! (I've not grown them before). What's happened in the past for you, OP?

Cosmos are one of those that really grow better from self seeding.

But if you want a specific variety they are awkward and very finicky.

For flowers that grow anywhere, including scrubland, like cosmos, I would sow a pinch of seeds into coir in modules and keep the nutrients low. And plant out when I have a decent root ball.

Leggy with few flowers and nothing like those you can buy in the garden centre .

To pinch or not to pinch is a dilemma.

My mum grows loads most years.
I try but they hate me.

she’s in Lancashire.

I-have had good and bad years with them. They always seem to do nothing till really late in the year. I pinched them last year and they were less leggy. But the best year I had I literally did nothing except plant them in the ground. I love them though and will persevere!

I want to know what garden centres are doing to produce such sturdy repeat flowering blooms.

You can’t direct sow can you?

I sow cosmos in the place I want them to grow (they don't seem fussy and I've had them do well in poor soil topped with bark chippings and accidentally left overcrowded in pots) after the risk of frost has gone and they always seem to oblige. I've never had any self-seeded ones come up despite letting them set seed most years.

You need to sow the newer varieties which are bred to flower earlier, e.g 'Cosima' or 'Candyfloss Red'. It's important to pinch them out as young seedlings and to keep deadheading them every day to keep them flowering. They need full sun.

I’ve always found cosmos really easy to grow from seed, it’s my go to annual as they flower for so long. I just stick them in a pot, south facing window, pinch out if I remember and plant straight out after hardening in May. I’m sorry they’re not happy with you, I’m sure climate plays a part.

Do you feed them? If so, don't.

IME pinching doesn't make that much difference, but some years they are like a jungle, last year I had one 🤷‍♀️

They grow them in ideal conditions and have staff that look after them and all the other seedlings all day. Also they chuck away the failures long before they get to the shop.

Greenhouse or conservatory for seedlings to be less leggy?

I started my cosmos seeds in the airing cupboard, to germinate them (seeds scattered onto wet kitchen paper, then fold the paper and put into a clear plastic bag) they germinate after 5 to 7 days)

Transplant into pots and grow on in the greenhouse until May when all risk of frost has passed (SW), then plant in their flowering position in full sunshine.

Can also plant them in large tubs, but keep them pinched so the don't look out of balance (best in a sunny border).

It was a crap year for them last year (I grow cut flowers as a major hobby and for sale) so it probably wasn’t you! Start about 6 weeks before your last frost date. Fresh seed, germinated somewhere warm (windowsill propagator works well for me). As soon as they’re mostly germinated, straight into a greenhouse or glass cold frame (even the sunniest windowsill will never provide enough all-around light). Pot them on when they’ve got a couple of true leaves. Pinch out the growing tip at 4-5 true leaves. Plant them out when last frosts have passed. I recommend Apricotta, Purity, Psyche White, Cupcakes varieties, Rubenza

I don’t think it was a good cosmos year, mine were ok but nowhere near the previous years, it was very hot and dry

My cosmos does better if I just chuck the seeds on a flowerbed and forget about it. If not, I keep it in the greenhouse until May and then let it free, but the bushier ones I had last year were the scattered seeds.

I grew them last year - sowed them in the garden just before a heatwave in July - very out of date seed so it was a case if they don't grow, nothing lost.
They were magnificent!

I seem to have a very low germination rate but the ones that did grow last year were magnificent. They always seem to fall over at some point though. Should I stake them?

I grew loads last year. They're so beautiful. Once a flower dies off, if you cut it at the base of the flower stem, it encourages more flowers to grow. Mine started off really leggy, but they eventually bloomed into huge plants with loads of flowers.

I tried cosmos for the first time last year. Got sooooo many flowers! You need to pinch the seedlings and then after they flower really prune the stems right back otherwise they will get huge and leggy. They want full sun for lots of flowers. Good luck!