When to plant dahlias in Seattle and Tacoma, WA

Plant dahlia tubers in Seattle and Tacoma May 10 – Jun 7.

Moderate Plant tubers

Why these dates

Seattle and Tacoma's typical last spring frost is March 2. Frost kills dahlias, and warm-season crops also need warm soil. Soil here stays cold for weeks after the last frost, so planting waits until about May 10.

West-side valleys. The Willamette Valley, Puget Sound and southern Oregon valleys. Long frost-free seasons, but soil stays cold and wet into May, so warm crops wait for warm soil, not just the last frost.

Difficulty: Moderate
Sun: Full sun
Spacing: 18 to 24 inches apart
Planting depth: 4 to 6 inches deep, eye pointing up
Frost: Killed by frost
Flowers: Blooms from midsummer until the first frost

Step by step

Pick a sunny spot with soil that drains well, and mix in an inch or two of compost.
Plant dahlia tubers May 10 – Jun 7, 18 to 24 inches apart. 4 to 6 inches deep, eye pointing up.
Don't water tubers until shoots appear, then water deeply once a week. Stake tall varieties when you plant so you don't spear the tuber later.
Harvest: Cut flowers when they're almost fully open, early in the morning. The more you cut, the more they bloom.

Varieties that do well here

Café au Lait
Bishop of Llandaff
Cornel Brons

Watch out for

Slugs and earwigs chew young shoots and petals. Use iron phosphate slug bait early in the season.

Tubers rot in cold, wet soil, so wait until it warms. West of the Cascades many gardeners leave them in the ground over winter under thick mulch; east of the mountains, dig and store them after the first frost.

Common questions

When is the last frost in Seattle and Tacoma, WA?

Typically March 2. In 9 years out of 10, frost is over by March 23. These are 1991–2020 NOAA climate normals for Seattle-Tacoma International Airport.

Is it too late to plant dahlias in Seattle and Tacoma?

The spring planting window runs through June 7. Later plantings may not have time to bloom well before the first fall frost, which usually arrives around November 23.

When do dahlias bloom?

Blooms from midsummer until the first frost. Cut flowers when they're almost fully open, early in the morning. The more you cut, the more they bloom.

Also plant in Seattle and Tacoma around the same time

Planting dates for dahlias in nearby areas

Portland, OR May 10 – Jun 7
Gresham, OR May 10 – Jun 7
Wilsonville and Canby, OR May 10 – Jun 7
Salem, OR May 10 – Jun 7
Eugene, OR May 10 – Jun 7
Roseburg, OR May 10 – Jun 7

Full planting calendar for Seattle and Tacoma · Dahlias in every city