Hartley Magazine

All the latest news, hints, tips and advice from our experts

Dahlia Overwintering

Lia’s dahlias are almost ready to be lifted and brought in

It is just about time for the dahlias that I planted in pots in the greenhouse in spring to come in for the winter, or else to be prepared for a winter outside. The latter is a bit of a risky game, particularly if we have a winter like last year’s. It chilled many dahlia tubers to their cores: not a thing they will put up with. It is always a toss up between taking the easy road and cutting down on work present and future, and taking the safer but more laborious route. Mine are planted in different places, and that will make a difference to what I choose to do with them. Those up at the allotment may have to come in, just because conditions up there are harsher than in the garden, and the soil is a good solid clay that will hang on to every drop of moisture and rot them through. But not everyone will be on such miserable winter soil, and my allotment is close to being one of the situations where dahlia queen Sarah Raven suggests leaving them in for the winter. She does this (on much better draining soil, I suspect) where she grows the dahlias that she uses as cut flowers. There are only other dahlias in such beds and so they all grow up at the same time and never crowd or shade each other out, and so she suggests cutting them back after frosts have blackened the leaves, and then mulching thickly with mushroom compost or similar to keep out the cold. I could try it and keep my fingers crossed that it doesn’t get too wet or too cold, and it is certainly very tempting. In the spring I just need to protect them from marauding slugs (I have seen slugs kill dahlias just through sheer persistence as the poor shoots try repeatedly to run the gamut and get chomped off every time). They might need a little staking as the growing season goes on, and occasionally pinching back to make them bushier and encourage them to produce more flowers, but that’s about it. Very worth a go if you are on well draining soil, and I have to admit even I am tempted to give it a try.

Where dahlias have been slotted in among other perennials they will get crowded and shaded out by the other plants early in the year, and will be particularly susceptible to the slugs. In this situation it is always worth lifting them, storing them and replanting them the following year. Dahlias in pots could go either way. Mine are tucked close to the house so are likely to be less subject to a hard frost than those out in the open garden, on the other hand a pot of soil can freeze solid, where the ground might not. Also, I need to put my tulips somewhere, so the dahlias are coming out. The trick is to wait until they are hit by a couple of light frosts before you lift them, to give them the definite signal that it is time to stop growing. Then lift and shake off the soil and leave the tubers to dry off before brushing off more dried soil. Don’t be tempted to wash them as this can lead to them rotting, but do snuggle the dry, cleaned tubers into some slightly damp compost or sand so that they don’t shrivel over winter. Store them somewhere cool but frost free, and they should be in perfect condition to plant up in big pots in the greenhouse next spring.