When to plant zinnias in Kent, Renton and Auburn, WA

Plant zinnias from seed, directly in the garden in Kent, Renton and Auburn, May 10 – Jun 21.

Easy Plant seeds in the ground

Difficulty: Easy
Sun: Full sun
Spacing: 9 to 12 inches apart
Planting depth: ¼ inch deep
Frost: Killed by frost
Flowers: Blooms about 60 to 75 days after sowing

Why these dates

Kent, Renton and Auburn's typical last spring frost is March 20. Frost kills zinnias, 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.

How to grow zinnias in Kent, Renton and Auburn

Prepare the bed: loosen the soil and mix in an inch or two of compost.
Plant seeds May 10 – Jun 21, ¼ inch deep, 9 to 12 inches apart.
Keep the soil evenly moist until sprouts appear, which can take one to three weeks in cool soil.
Harvest: Cut when stems are stiff right below the flower (give it a gentle wiggle test). Cut long stems often; the more you cut, the more they bloom.

Key numbers

70–80°FSoil to sprout
5.5–7.5Soil pH
60–75Days to bloom
Powdery mildewBiggest risk

Growing notes

What makes the difference in Northwest gardens, in plain language.

Wait for warm weather

Zinnias come from hot, dry regions and do nothing in cold soil. Seeds sown too early west of the Cascades often rot, and seedlings sit stunted and yellow. Sow once the soil is warm and nights are mild, usually late May to early June on the west side. They catch up fast: a sowing in early June often blooms by midsummer.

You can start them indoors a few weeks early, but transplant them young, since older seedlings don't like root disturbance.

Pinching and cutting

When a young plant is about a foot tall with three or four pairs of leaves, pinch out the top just above a leaf pair. The plant branches, and those branches give more stems and longer ones for cutting.

Cut flowers often and cut deep, down to a leaf pair low on the stem, so new branches have room to grow. Check for ripeness with the wiggle test: a stem that stays stiff just below the flower will last in the vase, while a floppy one wilts quickly.

Mildew, and east vs west

Powdery mildew coats leaves with white powder in late summer, when warm days and cool, damp nights alternate, a typical west-side pattern. Space plants for airflow, water the soil instead of the leaves and choose resistant varieties like Zahara. It looks bad but rarely stops flowering.

East of the Cascades, zinnias thrive in the heat and mildew is less of a problem, though steady water keeps them blooming. Slugs on young seedlings are the bigger west-side issue.

Common questions

When is the last frost in Kent, Renton and Auburn, WA?

Typically March 20. In 9 years out of 10, frost is over by April 8. These are 1991–2020 NOAA climate normals for Kent.

Is it too late to plant zinnias in Kent, Renton and Auburn?

The spring planting window runs through June 21. Later plantings may not have time to bloom well before the first fall frost, which usually arrives around November 10.

When do zinnias bloom?

Blooms about 60 to 75 days after sowing. Cut when stems are stiff right below the flower (give it a gentle wiggle test). Cut long stems often; the more you cut, the more they bloom.

Should I pinch my zinnias?

Yes, for cut flowers. Pinch the top when plants are about a foot tall; they'll branch and give many more long stems. Skip pinching on dwarf bedding types.

What is the white powder on my zinnia leaves?

Powdery mildew, a fungus common in late summer. Remove the worst leaves, water at the base and give plants more room. Next year, try resistant varieties like Zahara.

Why don't my zinnias last in a vase?

They were likely cut too early. Use the wiggle test, cut in the cool of the morning, strip the lower leaves and change the water often. Zinnias prefer clean water without much floral preservative.

Also plant in Kent, Renton and Auburn around the same time

Planting dates for zinnias in nearby areas

Seattle and Tacoma, WA May 10 – Jun 21
Everett, WA May 10 – Jun 21
Olympia, WA May 10 – Jun 21
Bremerton and Port Orchard, WA May 10 – Jun 21
Shelton, WA May 10 – Jun 21
Portland, OR May 10 – Jun 21

Full planting calendar for Kent, Renton and Auburn · Zinnias in every city