How to Prep and Plant Dahlias

Preparing the Soil

Choose the Right Spot:
Select a location that receives full sun—at least 6–8 hours of direct sunlight each day. Dahlias thrive in warmth and light.

Amend the Soil:
Dahlias prefer rich, well-draining soil. If you’re working with clay-heavy soil, dig down 10–12 inches and mix in 2–3 inches of well-rotted manure (store-bought is best) or high-quality compost. Blend it thoroughly into the soil for a loose, fertile bed.

When to Prep:
The ideal time to amend your soil is in the fall, allowing it to settle over winter. If that’s not possible, prepare it in the spring—3 to 4 weeks before planting.

Planting Dahlias

When to Plant:
Wait until the soil warms to 60°F and all danger of frost has passed. In many areas, this is around Mother’s Day in my part of the world.

How to Plant Tubers:
Dig a hole 6–12 inches wide and sprinkle in a couple of tablespoons of low-nitrogen fertilizer. Mix it well into the bottom of the hole.

Lay the tuber horizontally with the eye or sprout facing upward, about 4–6 inches below the surface. If the sprout is under 2 inches, leave it intact. If longer, trim it just above the tuber. Pushing through the soil will help produce stronger stems.

Backfill:
Gently fill in the soil, pressing lightly to eliminate air pockets and secure the tuber in place.

Staking

Individual Plants:
For a few dahlias, insert a 4–6-foot stake 1–2 inches from the eye at planting time to avoid damaging the tuber later. Anchor the stake 9–12 inches deep and tie stems every 12–18 inches as they grow.

Beds or Rows (Corralling Method):
For mass plantings, place 6-foot stakes at each corner and every 10 feet along the sides. Run twine or wire around the stakes at 18 inches and again at 36 inches to support the plants as they grow.

Watering

Early Watering:
No need to water until the tubers sprout (typically 3–5 weeks), unless you’re in a very dry area or using containers. In that case, water lightly once a week to keep the soil just moist.

Established Plants:
Once dahlias emerge, water deeply 3–4 times per week. Moisture should reach 8–10 inches down. A soaker hose or drip system is ideal, as sprinklers become less effective once plants mature.

Fertilizing

After the initial fertilizer at planting, wait until plants are about 12 inches tall to begin monthly feedings. Use a low-nitrogen fertilizer to encourage blooms instead of leafy growth.

Maintenance

Pinching:
When plants reach about 12 inches tall, pinch off the top 3 inches of growth to encourage branching. This leads to stronger stems and more blooms.

Stripping Leaves:
Once plants reach full height (especially over 4 feet), remove the bottom 12–18 inches of leaves to improve airflow and reduce mildew risk.

Labeling

Once your plants bloom, make sure each variety is clearly labeled so you can identify and divide them correctly in the fall.

With just a little prep and ongoing care, your dahlias will reward you with a season full of showstopping blooms. Happy planting!