The other day on Gardener’s Question Time, Bob Flowerdew gave as his “topical tip” the advice that you should leave your dahlias in the ground over the winter. He said that he’s learnt that the only reason people lifted dahlias was to take cuttings in the spring and if you didn’t want to do that you might as well leave them in the ground, making sure that you give them a good covering of mulch to protect from the frost. If only it were as simple as that.
In fact there are very good reasons to lift dahlias, whether you want to take cuttings or not. First, you are more likely to have a live plant after the winter. Dahlias left in the ground are susceptible to frost (despite the mulch) as well as to anything in the soil which might like to eat them. Secondly, if they are left in the ground they will emerge and come in to flower at least a month after plants which have been brought on in a cold frame. I value that extra month of flowering, especially when I grow them for cut flowers. Thirdly, the tubers will divide, so if you lift them you’ll get extra plants without the faff of taking cuttings.
This photo shows tubers which we have lifted this week and cleaned of soil. They will be put on trays in dry compost and stored in a shed until February when we’ll pot them up and put them in the cold frame. They’ll be in flower before the end of May. Those which we leave in the ground (we leave about a third of our total) won’t show their first shoots until then. Believe me Bob, its worth the extra effort to lift and store dahlia tubers.