There have been a number of questions raised recently online about caring for Dahlias in the Autumn and Winter. As you may have seen from my Instagram feed I have several varieties in my garden here at Dovewood. Whilst this in no way implies I am an expert I will share with you the knowledge I have gleaned about them over the years.
There is a certain amount of confusion and mis-information about what you should or should not do with these tubers. This is inclined to put you off trying these colourful plants but they really are not difficult to care for.
What sort of soil do you have?
There are two schools of thought about the best way to keep Dahlias from one year through to the next. The first is to leave them in the ground with a thick mulch over them to protect them from frost damage through the Winter. This is fine if your soil has good drainage. I have friends who live 10 miles from me and are fortunate to have a sandy soil, they never lift their Dahlias, and the plants survive well. For those of us who garden on heavy clay soil the risk of the Dahlia tubers rotting is too high. Clay soil gets very wet and cold during the winter.
Which variety of dahlias do you grow?
There are no hard and fast rules for what to do with commonly available varieties, so regardless of your soil type you may have to lift some tubers. The Bishop strain of Dahlias are hardy except for one which isn’t! If you have a variety that you are particularly fond of, and are in any doubt, lift it for the winter and replant the next year.
How to store Dahlias
After the first frost cut the stem down to 4″ above the crown. Gently loosen the soil around the plant and lift it out of the ground with a fork. Dislodge as much of the soil remaining around the roots being careful not to break off any tubers.
LABEL them! There is nothing more frustrating than having to guess what colour your Dahlia is when you go to plant them out the next year. To avoid this use a plastic plant label with a hole in it to tie onto the root of each plant with garden twine. Make sure to write clearly onto the label the colour even if you cannot remember the variety. Tie it around the root – not the stem which will wither – as the label will undoubtedly fall off if you do
Leave the plants in a dry place for a few days for any remaining foliage and stems to dry out, then store in a cool dark place. I put mine in buckets of dry sawdust which will draw out any remaining moisture. I hang the buckets up into the roof space of my shed but take them down periodically to check the tubers are dry and not getting eaten by rodents.
You can plant the Dahlias out in the Spring or early Summer after the danger of frost has passed. If you have left the tubers in the ground leave them covered, again until after the last frost. For us here in Dorset that means waiting until mid-May. You can check your average local frost date by Google-ing “Last Frost Date”. You can divide Dahlia tubers by removing one or two of the fat “sausages” off the root. Make sure there is an bud “eye” present. I had several of these small tubers come up away from the main tuber last year which I potted them up in the Spring and grew on successfully.
You may wish to stake the Dahlias when you plant them in preparation for their growth but you can wait until there is a mound of foliage, although the danger then is damaging the roots as you push the stakes in beside them.
If you don’t already grow Dahlias I certainly recommend trying them. Just one or two tubers will give you a solid block of colour in the border, and cut flowers for the house too!