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I'm growing some Cosmos in a multi-cell tray at the moment and they're coming along quite well, with the small plant being around 2" tall. My question is, should they stay in the multi-cell, or should they be potted on into a larger pot.

i grew these last year, i initially started in plug trays to about 2" and repotted into individual pots before planting out, they were about 12" plus tall when planting, what a fantastic show they put on

What size pots did you use after the plug trays?

depends on the tray size WH. I've just sowed some seeds in some plug trays and as soon as the plug is just about full of root they go into a 3" pot but these are commercial sized plugs (about 1" sq) so there won't be much compost in there.

The main thing is to keep them moving on without becoming pot bound otherwise they never really get over it and don't establish so well. But don't put them into too big a pot as there won't be enough root to absorb the excess moisture and it could lead to them rotting off.

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ntg

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Remember that a lone amateur built the Ark.
A large group of professionals built the Titanic

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The multi-cell that I'm using holds 24 plants, and each cell is around 1.5" square. They are at the 2" size now. Should I leave them, or pot them on now. Sorry to be such a pain, but I really am new to this, and desperate to get it right.

Hi.
Have you any cosmos seeds left - we just chuck them on the soil with the poppies during autumn or spring - or leave them to self seed and they are fine...Having said that, now that they are up I would put them into pots about an inch or two wider than the cells they are now in. You might have to step it up another pot size before you can plant them out but they should be ok.

I am a very big fan of cosmos, poppies and flax...along with tagetes these form the basis of my companion planting to attract/repel various insects/pesties and the first 3 have such gorgeous flowers and they look beautiful in amongst the veg.

Enjoy.

I don't usually (in fact, ever) pot anything on until it's got a couple of sets of propper leaves - not just the seed leaves.

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Updated November 17th - The Big Dig

HI Flummery, Do you not find they get to leggy and fall over with such a thin stem?

hi wh, i potted on into 3" or 4" pots, plus size was 1", it worked with me, i want to grow ome chocolate cosmos this year

my typing is terrible 2nite! plug size was 1" and mean't to say 'grow some', nearly the weekend

They#ll be OK in those plugs for some time as they are quite big. I normally sow into 40's at most unless you've sown more than one seed per plug and you'll need to be careful with the watering as thats a lot of wet compost potentially with only a small root ball in till it's grown.

As to thin and leggy - they shouldn't be unless you keep them too warm as they won't be crowded at that spacing ( again unless you've multi sown)

__________________
ntg

Never be afraid to try something new.
Remember that a lone amateur built the Ark.
A large group of professionals built the Titanic

http://grief-encounters.blogspot.com/

I pinch out the top of cosmos once they have two or three pairs of leaves. Then they bush out and don't become leggy. Repot once you can see the roots underneath the pots.

Thank you everyone for your valuable advice. Me thinks they have been to warm and comfortable.
I have now moved them out into the greenhouse,while there are no frosts, and cover them over with fleece of a night. Just have to wait and see if they survive . AS you can see, this has been a bit of a leaning curve to me.

Cosmos are one of my favourite annuals and I grow alot. I always start them in modules workhorse but they can get leggy really quickly. Like Cottage Garden I pinch out the top and this makes them bulk up a bit.

They really are beautiful flowers and I have a whole garden filled with every type of cosmos (I don't sow many other annuals). They were my mother's favourite too and her cottage garden always looked a treat. Mine tend to be a bit spasmodic in their growth due to northern climes so I never seem to get the same effect as she did.

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Aerodynamically the bumblebee shouldn't be able to fly, but the bumblebee doesn't know that so it goes on flying anyway.
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Never thought about pinching out, but does this effect the final height of the plant.