How to Grow Giant Dahlias

Dig a hole that is a bit larger than the root ball of the giant dahlia. Amend the loosened soil with a generous handful of compost.

Plant the giant dahlia so that the area where the stem joins with the roots, known as the crown, is just above the top of the soil. Pat the soil down and water until thoroughly moistened.

Place two or three 6-foot stakes around the plant. Attach the giant dahlia to the stakes with plant ties as it grows to keep it from breaking during high winds.

Water the plant whenever the top 1/2 inch of soil feels dry. Add moisture at ground level instead of pouring it over the plant. Feed once each month with 5-20-20 fertilizer, from the time of planting until the middle of August.

Pull weeds regularly to prevent competition for moisture and nutrients. Mulch around the plants with a 3-inch layer of straw at the end of June.

Remove all plant ties from the giant dahlia after the first fall frost. Pull the stakes up carefully to avoid damaging the plant's roots. Clip the foliage back to a height of 3 to 4 inches.

Begin digging 2 to 3 feet from the base of the plant to avoid nicking the dahlia's delicate root system. Lift the tubers from the soil when they are completely exposed and use your fingers to gently remove the remaining soil.

Store the tubers in a cardboard box with 4 inches of peat moss in the bottom. Cover the tubers with a 1-inch layer of peat moss, leaving just the tops of the stems above the straw.

Move the box to a dry location that maintains temperatures between 40 and 55 degrees Fahrenheit. Check the tubers every two to three weeks for signs that they are drying out, such as a shriveled appearance. Sprinkle lightly with moisture if necessary.

Divide the tubers with a sharp knife during March or April. Make sure that each clump has an "eye," which is a newly developed sprout. Replant the tubers in the garden after all danger of frost has passed.