Question
Hi Gill,

Couple of quick questions on Dahlias if i may...
I think it's touch and go in South of england whether to dig up / leave out dahlias. After losing one two years ago, i tend to err on the side of safety and dig out of pots, then replant after frosts (in pots as easier to control snails/slugs!!) My first question is: could i just move the pots into my shed instead of digging out??
Do i have to divide the plant regularly? What are the disadvantages of not dividing? (the two i currently have have grown considerably in just one year, with 30-40 or so tubers each)

If dividing is recommended, can i wait until sprouts start forming, as i find it difficult to see the eyes!! (and i guess another mini question is, will they sprout when they're out of the ground??)

Just one more....in pots, I'm using John innes No:3...do i have to replensh this totally every year, or can i just top dress with fresh compost?

Sorry for so many questions at once....hopefully you'll be able to make some sense of my ramblings!! I have bought another 6 dahlias for this years, so your advice would be very welcomed.

Many thanks, Mark

Answer
Hello Mark

First, allow me to apologise for the delay in getting back to you.  My service provider has been down for nearly a week!!

Right - now, Dahlia's left outside for the winter are usually killed by soggy wet ground rather than the cold!  I'd always advise taking them undercover, but don't leave them in their outdoor pots.  First you should cut down the top growth to about 2-3 inches.  Them turn the plant out of the compost and turn it upside down in a shallow wooden box (if you can lay your hands on one) otherwise just lay them on newspaper (upside down) and leave them for a few days to dry out.  Once the tuber and the inside of the stem is dry, brush, or rub off, as much of the old compost as you can.  Examine each tuber for signs of rot.  Where you find any, cut it out with a short garden knife and dust the wound with an anti-fungal powder (you can find this in any garden centre).

When all the tubers have been cleaned and treated, place them right way up into a box or crate and pack spent slightly damp compost around them covering the tubers completely, but leaving the stems visible.  Check them about every 4 weeks throughout the winter.  Cut out any rot that may occur and treat as above.  If any of the tubers look wrinkled and feel very dry you can soak them in a bucket of luke warm water for a few hours until they plump up.  Put them back into the compost.

I think it would be advisable to divide plants which have developed more than 3-4 tubers!  So get that gardening knife sharpened!  Yes, the tubers will shoot while they are out of the ground and you can divide them once these shoots have started to show.

I personally would replenish the whole of the growing medium each year (especially if the are growing as vigourously as yours!).  

Once they are up and away again, water and feed them regularly and I do hope that you get a really fantastic display this coming season.

Gill