Top Tips for Overwintering Dahlia Tubers

How many gardeners keep their dahlias from one year to the next? It is certainly less bother and probably doesn’t cost anymore to buy new ones every spring. If, however, you enjoy the process of gardening as much as the end result, and you think that the old cultural traditions are worth maintaining, there is one job which is essential at this time of year.

The Need to Lift and Store These Half Hardy Organs

With the milder winters experienced in recent years dahlias can often survive the winter if the tubers are left in the ground. You can improve their chances of survival by mulching the soil on top of the tubers with straw or old compost. The risk involved in doing so may be worth it in the milder southern climate, and especially where the soil is sandy. If you live in a colder northern area and your soil is heavy then leaving them outside is a gamble with the odds heavily stacked against you.

When to Lift and Store Dahlia Tubers

Traditionally dahlia tubers have been lifted after the first real frost of the winter when the tops have been blackened by frost. It’s not essential to wait for the first hard frost. Frost doesn’t benefit the dahlias. On the contrary too many severe frost will turn the tubers to mush. So if the ground the dahlias occupy is needed for other plants, like spring bedding for example, the dahlia tubers can be lifted whilst the tops are still green.

The Method For Lifting and Storing Dahlia Tubers

• Before cutting back the top growth tie a label at the base of the stem of each plant.
• Even if you don’t know the variety it’s a good idea to record its colour, height and flower type.
• Using secateurs cut the stems down to 20-30cms from the tubers.
• Push a fork into the soil about 30cms from the plants and lift them carefully so as to avoid damaging the tubers.
• Remove the excess soil from around the tubers then dry them off in a frost free place.
• Place upside down on slatted greenhouse staging for 2-3 weeks to allow any sap and moisture which would provide ideal conditions for fungal diseases to drain from the stems.
• Gently wash off any remaining soil, allow the tubers to dry again, and cut out any pieces of damaged tuber.
• Dust any cut surfaces with a powder composed of equal parts ground limestone and flowers of sulphur to prevent the entry of fungal spores.
• Put the tubers in deep troughs or boxes and cover them with dry sandy compost.
• Store the tubers in a fairly dark frost free place and keep them at a temperature of about 5 degrees centigrade. A garage attached to the house is ideal.

The Rewards for all This Care and Attention

Next spring when the days lengthen and the temperatures inside the greenhouse rise these food storage organs which you have nurtured over winter will fuel the growth of new shoots. From this growth many cuttings can be taken to produce new plants for next summer.