Planting Dahlias
How to Plant Dahlias
A guide from Bellingham Flower Farm
Dahlias are one of the most rewarding flowers to grow, offering so many colors and an abundance of blooms from midsummer through fall. Whether you’re planting a cutting garden or adding beauty to your landscape, getting dahlias off to a strong start makes all the difference.
When to Plant
Dahlias are sensitive to cold, so timing matters. Plant tubers in spring once the danger of frost has passed and soil temperatures have warmed to about 60°F. In Whatcom County, this is typically late April through May. A good rule of thumb is if the lilacs are blooming, it’s time to plant.
If you want a head start, tubers can be pre-sprouted indoors 4–6 weeks before planting out.
Choosing the Right Location
Dahlias thrive in full sun. Choose a spot that receives at least 6–8 hours of direct sunlight daily. The more sun they receive, the stronger the plants and the better the blooms.
Good drainage is essential. Avoid low spots where water collects, as tubers can rot in overly wet soil.
Preparing the Soil
Healthy soil leads to healthy plants. Dahlias prefer rich, well-draining soil with plenty of organic matter. Before planting, amend your beds with compost to improve structure and fertility.
Avoid over-fertilizing with nitrogen, which can lead to lush foliage but fewer blooms.
How to Plant Tubers
Planting dahlias is simple once you understand the basics:
Dig a hole 4–6 inches deep
Lay the tuber horizontally with the “eye” (growing point) facing up
Cover with soil, but do not water immediately unless the soil is very dry
Spacing depends on the variety, but most dahlias should be planted 12–18 inches apart.
Watering
Hold off on heavy watering until you see green growth above the soil. At this stage, begin watering deeply a few times a week, depending on weather conditions.
Consistent watering is key, especially during the heat of summer.
Pests
Once the dahlia are above ground the slugs and bunnies are notorious for eating them down overnight. We use Sluggo to prevent slug damage and plastic coverings can be used to determine rabbits. Once the plants are 6-8” they tend to be left alone.
Staking and Support
Many dahlia varieties grow tall and produce large blooms, so staking at planting time is recommended. This prevents damage to tubers later and keeps plants upright as they grow.
Options include wooden stakes, metal posts, or horizontal netting systems.
Pinching for Better Blooms
Once your plants reach about 12–16 inches tall, pinch out the center growing tip. This encourages branching and results in more stems and flowers throughout the season.
Ongoing Care
Keep beds weeded to reduce competition
Fertilize lightly once plants are established
Cut flowers regularly to encourage continuous blooming
Dahlias will continue producing until the first frost.
Harvesting Flowers
For the longest vase life, harvest when blooms are ¾ to fully open. Unlike some flowers, dahlias do not continue opening after being cut.
Cut early in the morning or late in the evening and place stems immediately in water.
