My poor Chocolate Cosmos!

Hey all. Can anyone advise me on what to do with my lovely chocolate cosmos. It seems to have a white mould or mildew on it. I was going to be putting it in the greenhouse for over winter. Would it help get rid of the mildew if I chop it back to earth for it to regrow next year?

I had been spraying it with mould spray but I don't think it helped. Any advice much appreciated

 

I think they need to be treated the same way you deal with Dahlias over winter, but that's only what I have read about them. I don't have one though so can't verify this.

 

Yes I am sure SussexG is right. I have just had a Google and found this - http://www.bbc.co.uk/gardening/plants/plant_finder/plant_pages/227.shtml . I didn't even know it had a tuber!

I wouldn't chop it back yet. Leave it to die back naturally - and your mildew problem will disappear at the same time. With Dahlias you let the frost kill the top growth, then lift the tubers. The first frost won't affect the tuber, which will be under the ground. The reason is that if you chop it back too early, whilst it is still warm, it may try to grow again - using up the valuable store of nutrients in the tuber that were meant for next year.

I once did this with Salvia patens, which is another tender plant with a tuber. I chopped it back too early, and put the tubers in a shed - and they all started to sprout again.

 

Thanks guys, I will just leave it alone for now then. I just wasn't sure if the mould would kill it completely if I left it. I have some dahlias too so advice is much appreciated!

 

Wow, thanks for that info, Sussexgardener & the link, Peter. I've been buying new plants each summer (although they are quite cheap in my local nursery). However, I will now overwinter them, same as dahlias.
:gnthb:

 

Thank you all for that info about overwintering cosmos, I bought some this year and I was going to leave them in the garden thinking they were perenials so If I had not popped in today I would have lost them, so thanks again.