London (change)
Today 10°C / 7°C
Tomorrow 13°C / 9°C
12 messages
27/02/2014 at 21:37

So last wednesday evening I sowed some cosmos seedlings in a windowsill propagator... Checking them this evening some of them are already at least 2.5" tall and touching the 'roof' of the propagator.

What should I do with them? There are still some cosmos seeds to germinate in there,  so should I pot on the germinated ones already? Or should I lift them & plant them deeper so they don't flop? I'm growing them in modular cells.


27/02/2014 at 21:53

Take the lid off the propagator and when they get to 3 or 4 inches tall then pot them on. Be sure to keep the compost damp though when you take the lid off. I usually find some of the seeds are slower to germinate. But when you take the bigger ones out to pot them on you may find you can put the lid back on the propagator to help the smaller seedlings catch up.

27/02/2014 at 21:57

Hi Bex - this has happened to me before with Cosmos - they go a bit wild!  So I now wait til March to sow, don't give them any heat (just a light windowsill) and prick them out, with quite a lot of the stem below the compost.

if you want to attempt to rescue the ones you have now, i would try planting them up individually, but you will need to plant them deeply to stop them keeling over.  And keep them off the heat

27/02/2014 at 22:11

Thank you! I was really shocked at the size of them, they aren't even in a heated propagator, just a bog standard windowsill one from Wilkos, AND they aren't even on a windowsill, just my dining table in a mostly unheated conservatory!

looks like some potting on is on the cards for this weekend then...

27/02/2014 at 22:53

I think that you have sown too early and with not enough light. If I were you I would start again in a few weeks time and start them off on a windowsill. They need lots of light.

27/02/2014 at 23:09

Yes.  A wee bit too soon to sow.  Nevertheless, all is not lost.  Remove the lid or not, is up to you.  From germination to more than half an inch high, causes me to worry.

Cosmos are among the fasted to germinate.  Try and apply the basic principle with seedlings.  'As soon as they are large enough to handle'  To me, that means.  As soon as I can gently get hold of them, or better still.  Soon after they develop their second pair of leaves, prick them out.

Now then.  One might assume that simply moving a seedling fro A-B would have little or no effect.  Sorry, I can't answer that one, but actually.  The pricking out and transplanting does have a great effect.  A simple test you can do.  OK. Take a pot or tray of seedlings.  Now then.   Prick out a few.  Keep them alomgside the basic seedlings.  You will see that the seedlings continue to shoot up, and sadly as so many have learned.  The seedlings soon become so leggy that, even when pricked out, many will wilt and die, others will not really come to anything.  Now look at the pricked out seedling.  For a while, it will appear to have come to a standstill.  Then it picks up.  If you are scientifically minded.  Take a closer look at it's structure.  The stem has thickened.  The leaves are so much more thicker and stronger.  I rest my case.

27/02/2014 at 23:41

let them " chill"


28/02/2014 at 09:17

Wow, lots of advice! I'll pot on the bigger ones to see if I can save any of them, but I'll also start off a new tray - so really slow, steady, and with lots of light is what I'm after? Maybe a bit of cold?

28/02/2014 at 09:50

Pot them on deeper in separate pots, pick out the tops, pick any flower buds off or they won't do anything at all, then grow another lot at the end of March, without a propagator, Last year I set seeds at the end of May, they lasted well through Autumn.

You can't plant them out till end of May at least, last year it was first week in June, imagine how big they will be by then.



28/02/2014 at 12:39

End of March for Cosmos, would that advice be good for up here in Scotland?

28/02/2014 at 13:11

As they cannot go out until after the last frost, you could easily wait til April to sow, especially in Scotland.

24/03/2014 at 19:43

Great question Bex2012, I was wondering what to do with my cosmos. Thanks.

Lots of info to take in.

email image
12 messages