Growing Dahlias – Dahlia Flowers and Dahlia Tubers in the Winter
Cutting Down and Lifting Dahlia Tubers
Many gardeners think thatplants should be left in the garden until the stems and leaves become blackened by frost. Although a slight frost does no harm at all to these plants, they certainly do not benefit from being frosted. Where possible, dahlias can be left to flower until the first frosts arrive, possibly in November. These last few dahlia are indeed valuable for cutting. Of course, it is not always possible to leave dahlia tubers in the ground until they are blackened; for example, if you have bedding dahlias where wallflowers, polyanthus, forget-me-nots and spring- are to be planted, then the dahlia plants must be cleared to make way for these other plants.
Before cutting down and lifting the dahlia plants, I would recommend tying a label at the base of the stems of each one. On this label write down details such as the name of the variety, colour, height and type. Even if you do not know the name of the variety, you can still put down the other details, and then the following spring you will have an idea of the colours and heights of each plant when deciding on planting arrangements and colour combinations.
After fixing the labels, the stems should be cut down to within 9 to 12 in. of the– certainly no less than this. It is best to use either a pair of secateurs or a strong knife for this job, as the stems are usually fairly tough by this time of the year.
The dahlia tubers should be lifted very carefully with a garden fork, taking care not to damage them in any way, as they are the food stores for the plant, and provide food for the growth of the shoots the following spring. Work about 1 ft. away from the stems.
Drying the Roots of Dahlia Tubers
Directly the tuberous roots are lifted, they should be dried off in a frost-proof place. Before doing this remove anywhich may be adhering to the tubers; cut away any damaged parts of the tubers and dust the cut surfaces with a powder composed of equal parts ground limestone and flowers of sulphur. The way I dry my dahlia tubers off, is to get a large wooden box, nail some thin strips of wood across the top, and then place the roots between these so that the stems are facing downward into the box. I leave them in this position for three or four weeks to allow the sap and any moisture to drain from the stems. If moisture collects in the stems and they are stored like that, then they will be affected by fungal diseases, which could spread and result in the death of the plant.
Storing the Roots
After the dahlia tubers have been dried off thoroughly, they are stored for the winter in a frost-proof place. The temperature can be allowed to drop to 1 to 2° C. (34° to 36° F.), but if it goes down to freezing point or below then the tubers will be killed. I would not recommend storing them in polythene bags because the roots give off a certain amount of moisture which collects on the inside of the bag and so encourages fungal growth on the tubers and stems. It is far better to wrap them in newspaper and place them in boxes. Alternatively, they can be placed in dry peat in boxes.
There is a tendency to keep them under greenhouse staging near heating pipes. This will cause the dahlia tubers to dry out and shrivel, and the buds will probably be killed. If this happens they will not start into growth in the spring. A frost-proof attic, cellar, garage or a cool room in the house is the ideal place for storing. While they are in store it is wise to check them over occasionally to see if any fungus is forming on the roots or stems. If this is so, dust them with flowers of sulphur.