We had our first serious frost here in Warwickshire on 6 November and the dahlias are now all beginning to die back. Keeping them in good shape over the winter is an important job at this time of year to ensure that we have great, good quality tubers for bringing on in the spring.
For those we want to bring indoors we cut back the stems and gently lift them from the soil. After scrapping off the majority of the soil we divide the clumps, if the tubers are large enough, into good strong plants. These are allowed to dry upside down in a frost free shed in the autumn sunshine before labelling (essential as you will never remember which one is which in the spring), wrapping in newspaper or soft brown paper and storing away in trays.
The objective here is to dry them sufficiently so that they will not rot over winter, to give them enough protection so that they do not get frosted and do not dry out too much.
We often have far too many tubers to dig up and bring indoors and so some plants have to take their chances in the ground. In the cut flower garden we cut back the foliage, cover with a good layer of dry straw from the local stables and then cover the bed with cloche plastic held down against the wind with bricks. The dahlias are planted in raised beds which provides some additional drainage when the ground gets very wet. We have had great success with this technique over the years and although the tubers sprout later than those indoors they soon catch up if you protect them well from the slugs. Not all will survive but enough do make it through.
The tubers kept in the frost free shed are usually potted up in about March, watered and brought on in the warmth before hardening them off and planting out after all danger of frosts has passed.
Now all that is required is a bit of good fortune and we will have a great show again next year!