Dahlias are one of those flowers that are a must for any sunny yard or deck. They grow from tubers but many times they are called bulbs. Dahlias come in many colors and sizes, they are container compatible, enjoy full sun and are easy to grow.
Start Indoors for a Head Start
Dahlias like to grow in warm soil, about 60°F, so if you can’t set them out until May or June then you can get a head start by starting them indoors in a pot or tub. Cover the tubers with about 2” of soil and water once you see growth breaking through. Once the soil has warmed up outdoors, transplant them to a warm sunny location.
Light–choose a location that gets at least 6 hours of full sun. If they do not get enough sun there will be fewer flowers.
Soil–the soil should be well-drained and if you have drainage problems consider putting in a raised bed amended with compost or a pot. Mulch around the plants to help conserve moisture, this is important in very dry areas with no summer rain.
Spacing and Depth–read the label on the package for the spacing and planting depth appropriate for the variety of Dahlia you are planting.
Feeding–work in a high quality fertilizer that is higher in phosphorus.
Watering–Dahlias like regular watering, but you should use drip irrigation to keep the foliage dry. Do not overwater your plants, this can lead to rotting of the tubers. It is best to deep water, less frequently.
Staking Your Tall Dahlias–You should give support to your taller varieties, especially the dinner plate size Dahlias. The stakes can be put in at planting time or added after the plants have begun to grow. Just make sure to not damage the tuber when putting in the stake. Use some twine to tie the stem to the stake.
Getting the Most Flowers from Your Dahlias
If you are growing the large dinner plate varieties and really want the largest flower, consider removing the lateral flower buds and only keep the single terminal bud. This will put all of the energy into developing that single large flower. Conversely if you want more flowers, remove the terminal bud, this will cause more lateral buds to form. Remove the spent flowers as well on all plants, this will encourage the plant to produce more flowers.
Winter Care of Dahlia Tubers
Dahlias do not like to be in wet or freezing conditions over the winter, so it would be best to lift the tubers and store in a cool, dark, dry location over winter. Once the tops have been killed back from a light frost, dig up the tubers, careful to not damage them, and cut off the dead plant about two inches above the tuber. Remove any pieces that are rotten. Wash off the clump and allow to dry for about two weeks. Store over the winter in sawdust, peat moss or put them in a paper bag (not plastic) or cardboard box. Put them in a place that will not freeze over the winter such as a garage, basement, or even a cellar. Before planting the following spring you can divide the clump of tubers, but when dividing, you should have at least 1-2 eyes per clump. Dividing is not necessary unless the clump is really big.