Dahlias produce stunning late-season flowers providing an abundance of blooms from midsummer through fall in a rainbow of colors and a multitude of shapes and sizes. As gorgeous as they are, they can seem intimidating to grow but they are actually quite easy with a few simple instructions.

About Dahlias

Dahlias are native to Mexico and South America where their tubers were originally grown by the Aztecs as a food source. They are tuberous perennials that grow into bushy plants each year ranging in height from 2-5’+. While they are considered perennials, their tubers are quite sensitive to cold and wet conditions and are usually dug from the ground and stored in the winter below zone 8.

Types of Dahlias

There are multiple types of dahlias as defined by their form and size. The most common include

Ball and Pompon dahlias have globe-shaped blooms with a swirl of florets. They are typically small to medium in size.

Decorative dahlias have flat-tipped petals that sometimes curve at the ends and can have notched tips. They can be Formal Decorative with their petals evenly spaced and uniform or Informal Decorative with slightly irregular petal arrangement. Decorative dahlias are generally are larger in size with the largest considered Dinnerplate dahlias.

Anemone dahlias feature an outer ring of petals around an interior pincushion.

Cactus dahlias are double flowered with a long pointy ray of petals.

When to Plant Dahlias

Plant dahlias no earlier than two weeks after the last frost. For cut-flower production, dahlias are often planted in late April or early May. The soil temperature should be at least 55 degrees when planting.

Planting Considerations

Location - Dahlias grow best in a location that has good drainage and at least 6-8 hours of full sun. They prefer the morning sun and an area that offers some wind protection. They benefit from a rich soil with a pH level of 6.0 to 7.5. Heavy clay soil should be amended with compost or sand to provide better drainage.

Support - Dahlias will need support as they grow either in the form of stakes or netting.

Space - Dahlia plants can grow quite large and will need space to grow. Planting them too close can cause the plants to not receive enough light or airflow.

Planting Dahlias

Plant dahlias in a 6-8” hole or trench. We recommend adding some compost first so that the dahlia is 3-4” deep. We suggest placing the stakes in the ground for support or netting at the time of planting so as not to accidentally puncture the dahlia tubers later. Do not water the tubers when planting until sprouts are 1-2” above the ground. Dahlias should begin blooming 8 weeks after planting.

Growing Dahlias

Fertilize - After sprouting, dahlias benefit from a low-nitrogen liquid fertilizer such as 5-10-10 or 10-20-20. Fertilize every 3-4 weeks.

Pinch - When dahlias are about a foot dahlia, many growers will “pinch” or cut 3-4 inches from the thick hollow stem at the center of the plant to increase stem count and length. This can also be achieved by taking a “deep” cut after the first flowers appear. Either way, try not to do so before a heavy rain as the hollow stem can fill with water and rot the tuber.

Watering - During dry times, water dahlias 2-3 times a week. We recommend ground watering, preferably with drip tape.

Deadheading - To encourage plants to continue providing numerous blooms throughout the season, deadhead as flowers fade.

Pests - Deer normally do not bother dahlias if there is another food source readily available nearby. The most common pests for dahlias are insects including Japanese beetle, cucumber beetle, aphids, thrips and earwigs.

Harvesting Dahlias

It is best to harvest dahlias in the morning when temperatures are cooler. Dahlias should be cut when they are in full bloom. Unlike other flowers, dahlias will not continue to open after they have been cut. To encourage continued growth, cut the stems long to just above a bilateral leaf node. Side buds may be trimmed off or left on depending on preference. Dahlias should last 5-7 days in a vase.