Make sure they’ll be protected over winter.
Dahlias have grown very well this year and produced masses of colourful and attractive flowers. They started to flower in late summer and because of the sunny, mild autumn they continued to bloom up to the end of October when the weather turned much colder.
Dahlias originate from Mexico and are not hardy. They grow from a fleshy root tuber and naturally die down in winter and re-grow the following spring. Traditionally, dahlia tubers were always lifted in autumn and stored for the following spring when they were either re-planted into the ground or started into growth in large pots to provide new cuttings. In well-drained soils and mild areas, the tubers will often survive the winter, but in cold districts or wet, clay soils it’s best to lift them now, before winter really sets in. A few frosts at this time of the year will blacken the stems and foliage, but it won’t harm the fleshy tubers in the soil. This frost damage does, however, serve as a timely reminder to deal with your dahlias.
If you’re debating whether or not to lift your tubers, one more thing to bear in mind is very often when left in the soil over winter, new shoots in spring are often attacked by slugs, which sets back growth.