Dahlias are one of the most popular garden plants because of the wealth of colour the blooms lend your green space. Dahlia flowers are usually planted in the spring, either in containers or in the ground, and bloom from midsummer through the first hard frost of the year. At that point, it is best to remove the flowers from the ground, either saving the tubers or disposing of them and using new tubers in the spring. Dahlias are either single flowering, with one row of evenly spaced petals or double-flowering with several rows of evenly spaced petals.
Divide the tuberous roots saved from the prior fall. The best time to divide the roots is after the eyes of the flower have sprouted. When dividing the roots, do so while the new growth is less than 1 inch.
Cut the clump of roots with a sharp knife. You should cut the clump into individual tuberous root groupings with each grouping having one "eye" or sprout. You will find the eye where the tuberous root and the stalk of the previous year's plant join together.
Choose a 6 to 8-inch pot and fill with good potting soil, leaving at least two inches of space at the top of the pot. Do not pack the soil down.
Lay the tuberous root on its side, eyes facing up. The eye must face up or it will not grow.
Cover with soil. Again, do not pack the potting soil down. Once repotted, fill in the soil around the tubers as they develop until the surface is level.
Put the tuberous clumps in shallow trays or a warm, moist area for a few weeks prior to cutting so that the plants sprout well. Let the areas with cuts dry for several days before actual planting or dust with sulphur or captan prior to planting. Small Dahlia's should have about two feet of space each, large flowering Dahlias need three or four feet of individual space. You can place a stake with each planting for support as the flower grows. Dahlias require a lot of water so keep the soil moist.
The shoots will be tender and can be easily broken so handle with care. Dahlias are sensitive to cold. Keep them inside until the last spring frost date has passed.