Tuber-grown dahlias can add a dramatic accent to your flower garden. But when you consider the cost, they can be an expensive accent as well. Dividing them, even in hardiness zones 7 and above, where they could successfully overwinter in the ground, allows for division and sharing or propagation for your own use. This reduces the overall cost, especially when you are growing the more expensive specialty varieties.
Difficulty: Moderately Easy
Dig the dahlia clumps gently with your spade or spading fork after the first frost has blackened the foliage or at the end of October in frost-free areas. Begin to dig several inches from the base of the plant to avoid damaging the tuber.
Wash the soil from the tuber gently with a jet of water from your garden hose and inspect for disease or insect damage.
Turn the tubers upside down to allow the necks to drain and leave in a dry, airy space for two weeks to dry completely. Do not place directly on a concrete surface, as this will draw moisture from the tuber.
Divide the tubers now if you want to share or multiply your clumps. Cut away any damaged tissue and divide each tuber into healthy sections with a sharp knife, making sure that each has one or more eyes or growth points. The growth point will look like a small pimple on the end of the tuber closest to the clump.
Mark the plant variety on each tuber with a permanent marker.
Dust each tuber with powdered sulfur to help prevent diseases.
Cover the dahlia tubers with dry sand, vermiculite or peat moss and store in a wooden box, bushel basket or sturdy cardboard box. Don’t store in soil or the tubers will be encouraged to grow before the appropriate time. Store in an area that remains at a temperature between 40 and 45 degrees Fahrenheit.
Inspect every few weeks to check for disease or shriveling.