Overwintering tender tubers/bulbs

borgadr

It's going to be my first time overwintering tender tubers/bulbs and I'm looking for some advice.  I have a canna, some polianthes tuberosa and dahlias (grown from the GW free seeds). 

My choices are:
- a greenhouse which is heated to remain above 5 degrees
- a garage which is unheated and detached from the house. I stupidly never took the temperatures in there last winter, but I'm not sure that it ever freezes in there. The air in there seems quite damp over winter though
- a small brick out-house at the back of the garden that I use as a potting shed. It seems to be drier than the garage, perhaps because it's better ventilated (less well sealed!)

Should all of them go in the greenhouse, or would I be pretty safe storing them in the garage or out-house?  And am I OK just storing them in pots of dry compost/soil? (do they need an occasional watering??)

I also have (hardy) tree lily bulbs currently in pots. Can I just leave them out where they are (let them get rained/snowed on) or should I bring them under cover and keep them dry?

Fairygirl

The lilies will be fine - but will possibly benefit from some shelter from the worst of winter weather - against a house wall is ideal.
Of the others, I've only grown Cannas and Dahlias. They just need to be consistently frost free. A greenhouse will probably be fine in most areas of the UK. The outhouse will also probably be fine, as damp cold is never good for any plant, but a drier building is easier as you can use fleece or cardboard boxes etc to protect from colder weather. 

You'd have to judge for yourself though, depending on your climate. I used to bring my cannas into the house to be safe, as it can be too cold in my little greenhouse or a cold frame etc for those here.  I overwintered them in a conservatory when I had one  too. They are also fine in a porch or similar. 

borgadr

Thanks @Fairygirl. I'll try the outhouse then for the canna and the polianthes, and find a way to extra-insulate them. Space is at a premium in the greenhouse as we get into spring. If there's an exceptional cold spell I can always move them. Worst-case: lesson learnt for next year!

I did have an extra thought though. Since I do have lots of dahlias and don't mind losing a few, for those ones I'll split them between all 3 locations regardless of weather and see how many survive.

Are they OK if their compost dries out and stays dry?

Fairygirl

I'd say it would be ok - generally, but it's usually better if they aren't absolutely dry for a very long time, in case they just shrivel up. Some people wrap them in newspaper, some keep them in boxes with a little compost or sand to stop them drying out completely, and some just leave them on shelving, so it's usually a case of experimentation. They can often absorb enough moisture from the air to keep them right, without being wet.
Getting the right balance is often trial and error.