Dahlias are showy, versatile flowers that grow from tuberous roots, or tubers. With an almost endless selection of varieties, the blooms of the dahlia can be double or single, varying in size from petite 2-inch flowers to blooms the size of a dinner plate and heights ranging from dwarf, 12-inch varieties to giant 6-foot stunners. For best results, divide dahlia tubers on a cool, overcast day in March or April.
Select a spot for the dahlias before you divide them, as the dahlias will benefit from being planted as soon as possible. Dahlias will do best in a spot where the dahlias will be exposed to a minimum of six hours of sunlight per day and protected from strong winds. Soil should be deep and well-drained.
Cultivate the soil to a depth of at least 10 to 12 inches about a month before you plan to divide the dahlias. Use a spade or tiller. Work in 2 to 4 inches of organic material such as well-aged manure, compost or shredded bark, along with a balanced granular fertiliser such as 10-10-10 (nitrogen-phoshorus-potassium). Apply the granular fertiliser at a rate of 0.907 to 1.81 Kilogram of fertiliser for every 100 square feet of planting space.
Divide dahlia tubers when the tubers have sprouted and the shoots are less than an inch long. Handle the tubers carefully, as the shoots will break easily. Use a sharp knife to divide the tubers. Be sure every section has at least one "eye," which is the point where new growth will appear. If you are unable to see any eyes, place the tubers in a box filled with damp pet moss. In a few days, the eyes should appear.
Dig a hole in the prepared spot for each divided dahlia tuber. Allow between 1 and 3 feet between each tuber, depending on the variety. Plant the tubers sideways, 6 to 8 inches deep with the eyes facing up.
Water the area to saturate the ground immediately after planting. Keep the soil constantly moist, but don't allow it to become soggy.
Spread 3 to 4 inches of mulch around the dahlia plant to keep the roots cool and retain moisture. Use an organic mulch such as shredded bark, straw or compost.