HOW TO PLANT DAHLIA

Dahlias are late-season flowers that bloom from midsummer through the first frost, offering a vast variety of colors, patterns, sizes, and flower forms that can be small border plants or giant plate-sized blooms atop 6-foot plants.

Dahlias are perennials in warmer climates and considered annuals below USDA hardiness zone 8, and these flowers grow best in full sunlight with well-drained soil and frequent waterings during the growing season. Because this species of flower is toxic to both dogs and cats, it's best to plant dahlias away from areas that pets can access.

Light

For optimal blooming, dahlias need at least 6 to 8 hours of full sun daily. In regions with similar climates to their natural habitat (USDA hardiness zones 8 and above), providing shade during the hottest part of the afternoon can be beneficial.

Soil

Dahlias prefer rich, loamy soil with plenty of organic matter that drains well. If you're unsure of your soil being rich enough, mix in some compost. Also, if your backyard soil tends towards a denser clay, add sand, peat moss, or manure to loosen the soil texture for better drainage. Dahlias thrive in a neutral soil pH of around 6.5.

Water

After planting dahlia tubers in the spring, do not water them until green growth sprouts above the surface. These flowers do not need water before their root system develops.

Once sprouted, water your dahlias once or twice a week. Make sure to water deeply, as large tubers may be planted six inches deep. If summer days are especially hot and dry, you may need to water more frequently and never let the soil dry out.

Temperature and Humidity

Timing is especially important when it comes to planting dahlias, as they'll struggle to establish in cold soil. Wait until the final spring frost has passed and the ground temperatures have reached 60 degrees Fahrenheit.

You can start tubers in containers indoors—perhaps in a garage or greenhouse—to get them off to a quick start. It's safe to plant dahlias outdoors when all danger of frost has passed. If you plan to dig up tubers and store them indoors for winter, make sure your storage area has a little humidity so they don't shrivel up and dry out.

Fertilizer

Dahlias are heavy feeders—the more food they receive, the larger the plant will grow. Fertilizing your dahlias makes the flowers grow larger and in higher numbers. Use a fertilizer with a high percentage of phosphorus (perhaps a 10-30-20 ratio) to promote blooming. For the amount, follow the product label instructions. Do not use fertilizer with a high percentage of nitrogen. Too much nitrogen creates lush foliage, but few blooms.4

If you plan to dig up and store your tubers for winter, stop fertilizing your plants at the end of August. This discourages more growth late in the season as you prepare the tubers for dormancy.