Horticulture and Crop Science
2021 Coffey Rd., Columbus, Ohio 43210-1086
Growing Dahlias
HYG-1245-92
Jack Kerrigan
Dahlias are considered one of the most spectacular garden flowers. They are also thought to require a great deal of care. Both of these statements are true to some extent. There is a great variety of form in dahlias, from the showy dinner-plate size to the bright, little single ones. Dahlias require some special care, especially lifting for winter storage. However, with minimum care, beautiful dahlia blooms will grace your garden from July until frost. Dahlias should be planted in a sunny location. The soil should be rich and well-drained with a pH of about 6.5. Wait until all danger of spring frost is past before planting.
Bedding dahlias can be planted 9 to 12 inches apart. The smaller- flowering types, which are usually about three feet tall, should be spaced two feet apart. The taller, larger-flowered dahlias should be spaced three feet apart. Dig the planting hole slightly larger than the root ball of the plant and incorporate some compost or sphagnum peat moss into the soil. Plant dahlias so the crowns are just above soil level. Tall, large-flowered cultivars will require support. Place stakes (five to six feet tall) around plants at planting time and tie stems to them as the plants grow.
Dahlias tend to have shallow roots so be careful when cultivating. About the end of June, mulch plants with well-aged compost, aged manure, peat, or straw. Water plants regularly if rain is insufficient but avoid wetting the foliage. Dahlias require a rich soil; a commercial fertilizer low in nitrogen, such as a 5-20-20, worked into the soil a month before planting is good preparation. As plants grow, a monthly feeding will encourage large blooms. If using a granular fertilizer, water it in thoroughly after application. Do not fertilize dahlias after mid-August.
