Cosmos advice requested

Hello
I have been growing cosmos from seed for four years now, and I still can't crack the etiolation problem. I start them off in a heated propagator then take them out as soon as they germinate. I then put them in the coolest part of the house (unheated, glass-roofed covered area down the side) under grow lights. But they still shoot up and become etiolated and sometimes just flop over.
Can anyone suggest anything? What sort of temperature is a good one post germination? Maybe not germinate in a propogator (but that ought to work, surely?) They are being removed from it literally within an hour of germination sometimes.
On the plus side, things do usually turn out ok in the end, but I'd like to get it right, rather than have to take remedial action.

 

I grow mine hard. Once they germinate, they're put outside in a sheltered spot during the day, as long as it isn't too windy, then brought back indoors each evening. They don't need any extra warmth once they've germinated and it's best to get them used to outside conditions early on, so grow 'em tough!

I know it's a leap of faith to do this, but try putting at least some of them outside during the day and see how they do for you.

 

If they've grown too tall, rather than just pinch them out, cut them back(ie be-head them ) by a third.
It may be that they are growing up for light, assuming you have planted them in individual pots (5"), space them out by a pots width at first and more as they grow bigger.
Perhaps you start them too early, its so tempting ! Sowing now will see them flower in July-August.

 

Before I had a porch - no greenhouse, I used to sow them in trays outside. They grew well. They are fast germinaters. They don't need coddling.

 

I sowed some seed on Saturday and they are all up already. I shall try this approach as I have just bought a cheap cold frame and it's sitting empty! I have plenty more seed for later sowings if they fail.

 

I grow mine in an unheated greenhouse, sown this year 5th April and all popping up about 5 days later.

 

Thanks all.

They are in 3" pots, which I think is enough room.
In an unheated area with a glass roof, so plenty of light, but getting a boost when there is no direct sun, from grow lights.

Temperature has to be the key...?
I had thought that because they are half hardy, outside would be a bit to cold, certainly in early March, when I sowed them, but maybe not as long as there are no frosts?
Greenhouse and cold frames are options, although the former can be very cold (colder than outside) at night but not sub zero now.

I really want to stop this happening rather than resorting to remedial action. I can and have buried some of the bendier ones (even before they get their true leaves). Cosmos seem to tolerate that. I can't pinch out yet as not enough leaves, but always do that in due course anyway.
I suppose the answer is, for next year's March sowings, to experiment by doing multiple simultaneous batches in different locations.

On the bright side, my current efforts are a lot better than my first rather desultory attempts at growing flowers from seed back in 2019. (But then they ought to be really... )

 

Sowing too early will be the main problem. It just encourages that legginess/etiolation if there's too much heat and not enough light. If you sow a bit later, you can get them outside with basic protection, as others are doing, which will encourage slower, healthier growth.

 

I agree with Fairygirl. Sowing too early is your main problem. Cosmos are quick germinating seed. I haven't sown mine yet. May is plenty early enough, then you do not have to worry about low light or temperatures.

 

They are one of the last on my list to sow because I need the space for other plants to get going first. I will sow them soon but have found that with longer daylight and more natural heat, they catch up and look better than ones I've sown earlier. I do molly coddle them a little and grow them on in the greenhouse where the extra warm helps.

 

Mine are growing on a South facing window. Take out the growing point to promote bushy plants.

 

I haven't sown mine yet, I usually wait till the end of April, start them indoors, out to the g/h when small plants, planted out in the garden at the end of May.

 

With cosmos I find that after they germinate I wait until the first true leaves are growing well .I then prick out into small pots .soon as they are four inch I nip out the growing tip (just the middle bit )
I then continue to grow on in this pot and repeatedly nip out the centre grow point.the plant will start branching out and forming like a bush.I usually leave until towards the end of June to plant out.
Don't put them too close when planting in the final place.. They will carry on branching out .mine spread a good 24 inch and must have had around 200 flowers .Will find photo for you

 

I've just sowed a few Xanthos and put them in my unheated porch but it faces south, so I have to be careful. If they don't look good I'll try again in a couple of weeks and leave them outside.

 

I sowed some cosmos outside a week or two ago (along with sunflowers/poppies and others). Half have sprouted and half haven’t. Not sure if the ones that haven’t is because it’s old seed or just a bit too cold for them yet. Will give it another week before trying those again. My attitude to seed sowing these days is if they don’t grow outside I don’t bother as I can’t be bothered with the in and out of hardening off and those sown outside seem tougher and less fragile.