Oregon · Washington · Idaho
When to plant cosmos
Plant in the garden: Portland and Seattle May 10 – Jun 21; Spokane May 15 – Jun 26; Boise May 1 – Jun 12; Bend Jun 16 – Jul 28.
Your dates in
Cosmos are tall, feathery annual flowers from Mexico in the daisy family, grown for cut flowers and pollinators. Classic Cosmos bipinnatus has pink, white and crimson single flowers on 3- to 5-foot plants, while Cosmos sulphureus is shorter, with yellow and orange blooms. Goldfinches eat the seeds once the flowers fade.
Puts cosmos on your free plan, with dates for your town and a spot in your beds.
- Difficulty
- Easy
- Sun
- Full sun
- Spacing
- 12 inches apart
- Planting depth
- ¼ inch deep
- Frost
- Killed by frost
- Flowers
- Blooms about 60 to 80 days after sowing
Airy, easy cut flowers that bloom from midsummer until frost. Poor soil is fine; rich soil gives you leaves instead of flowers. Sow once the soil warms, or start them indoors where summers are short.
Cosmo planting dates
| Towns | Start seeds indoors | Plant in the garden |
|---|---|---|
| Portland, OR, Seattle and Tacoma, WA | Mar 29 – Apr 12 | May 10 – Jun 21 |
| Spokane, WA, Astoria, OR | Apr 3–17 | May 15 – Jun 26 |
| Boise and Meridian, ID | Mar 20 – Apr 3 | May 1 – Jun 12 |
| Bend and Redmond, OR | May 5–19 | Jun 16 – Jul 28 |
Dates for six main cities. For any of the other 80 towns, type it in the box at the top of the page or browse all towns.
| Gresham, OR, Hillsboro and Beaverton, OR, Oregon City and West Linn, OR, Portland, OR, St. Helens and Scappoose, OR, Wilsonville and Canby, OR | Mar 29 – Apr 12 | May 10 – Jun 21 |
|---|
| Corvallis and Albany, OR, Cottage Grove, OR, Eugene, OR, McMinnville and Newberg, OR, Salem, OR | Mar 29 – Apr 12 | May 10 – Jun 21 |
|---|
| Ashland and Talent, OR | Apr 1–15 | May 13 – Jun 24 |
|---|---|---|
| Grants Pass, OR, Medford, OR, Roseburg, OR | Mar 29 – Apr 12 | May 10 – Jun 21 |
| Astoria, OR, Brookings and Gold Beach, OR, Coos Bay and North Bend, OR, Newport and Lincoln City, OR, Tillamook, OR | Apr 3–17 | May 15 – Jun 26 |
|---|
| Bend and Redmond, OR, Klamath Falls, OR | May 5–19 | Jun 16 – Jul 28 |
|---|---|---|
| Burns, OR | May 7–21 | Jun 18 – Jul 30 |
| Lakeview, OR | Apr 30 – May 14 | Jun 11 – Jul 23 |
| Madras, OR | Apr 14–28 | May 26 – Jul 7 |
| Prineville, OR | Apr 27 – May 11 | Jun 8 – Jul 20 |
| Baker City, OR | Apr 20 – May 4 | Jun 1 – Jul 13 |
|---|---|---|
| Enterprise and Joseph, OR | Apr 19 – May 3 | May 31 – Jul 12 |
| Hermiston, OR, Pendleton, OR | Mar 22 – Apr 5 | May 3 – Jun 14 |
| Hood River, OR | Mar 16–30 | Apr 27 – Jun 8 |
| John Day, OR | Apr 23 – May 7 | Jun 4 – Jul 16 |
| La Grande, OR | Apr 3–17 | May 15 – Jun 26 |
| Ontario, OR | Mar 17–31 | Apr 28 – Jun 9 |
| The Dalles, OR | Mar 14–28 | Apr 25 – Jun 6 |
| Bremerton and Port Orchard, WA, Everett, WA, Kent, Renton and Auburn, WA, Olympia, WA, Seattle and Tacoma, WA, Shelton, WA | Mar 29 – Apr 12 | May 10 – Jun 21 |
|---|
| Anacortes, WA, Bellingham, WA, Friday Harbor and the San Juans, WA, Mount Vernon and Burlington, WA, Oak Harbor and Whidbey Island, WA | Mar 29 – Apr 12 | May 10 – Jun 21 |
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| Aberdeen and Hoquiam, WA, Forks, WA, Long Beach and Ilwaco, WA | Apr 3–17 | May 15 – Jun 26 |
|---|---|---|
| Port Angeles, WA, Port Townsend, WA, Sequim, WA | Mar 29 – Apr 12 | May 10 – Jun 21 |
| Centralia and Chehalis, WA, Longview and Kelso, WA, Vancouver, WA | Mar 29 – Apr 12 | May 10 – Jun 21 |
|---|
| Chelan, WA, Wenatchee, WA | Mar 14–28 | Apr 25 – Jun 6 |
|---|---|---|
| Leavenworth, WA | Apr 5–19 | May 17 – Jun 28 |
| Omak and Okanogan, WA | Apr 3–17 | May 15 – Jun 26 |
| Winthrop and Twisp, WA | Apr 10–24 | May 22 – Jul 3 |
| Ellensburg, WA, Yakima, WA | Apr 3–17 | May 15 – Jun 26 |
|---|---|---|
| Ephrata and Quincy, WA | Mar 18 – Apr 1 | Apr 29 – Jun 10 |
| Goldendale, WA | Apr 14–28 | May 26 – Jul 7 |
| Moses Lake, WA, Tri-Cities (Pasco, Kennewick, Richland), WA | Mar 23 – Apr 6 | May 4 – Jun 15 |
| Sunnyside, Grandview and Prosser, WA | Mar 27 – Apr 10 | May 8 – Jun 19 |
| Walla Walla, WA | Mar 14–28 | Apr 25 – Jun 6 |
| Colville, WA, Pullman, WA, Spokane, WA | Apr 3–17 | May 15 – Jun 26 |
|---|
| Bonners Ferry, ID, Coeur d'Alene and Post Falls, ID, Sandpoint, ID | Apr 3–17 | May 15 – Jun 26 |
|---|
| Lewiston, ID | Mar 14–28 | Apr 25 – Jun 6 |
|---|---|---|
| Moscow, ID | Apr 3–17 | May 15 – Jun 26 |
| Boise and Meridian, ID | Mar 20 – Apr 3 | May 1 – Jun 12 |
|---|---|---|
| Emmett, ID | Mar 26 – Apr 9 | May 7 – Jun 18 |
| McCall, ID | May 18 – Jun 1 | Jun 29 – Aug 10 |
| Nampa and Caldwell, ID | Mar 25 – Apr 8 | May 6 – Jun 17 |
| Burley and Rupert, ID, Pocatello, ID | Apr 3–17 | May 15 – Jun 26 |
|---|---|---|
| Idaho Falls, ID, Twin Falls, ID | Apr 4–18 | May 16 – Jun 27 |
| Rexburg, ID | Apr 7–21 | May 19 – Jun 30 |
| Salmon, ID | Apr 13–27 | May 25 – Jul 6 |
Cosmo year at a glance
| Task | J | F | M | A | M | J | J | A | S | O | N | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Start indoors | Mar | Apr | ||||||||||
| Plant | May | Jun | ||||||||||
| Cut flowers | Jul | Aug | Sep | Oct |
Around Portland. Colder towns, especially east of the Cascades, run a few weeks later; the table above has your town's planting dates.
How to grow cosmos
- Start seeds indoors on your city's dates in trays or small pots under a grow light or in your sunniest window. Or skip this step and buy young plants (starts) at a garden center.
- Harden off the young plants: about a week before planting, set them outside for a few hours a day, a little longer each day.
- Plant them in the garden on your city's dates, 12 inches apart. If you plant seeds instead, sow them ¼ inch deep.
- Water deeply once or twice a week rather than a little every day, and mulch once the soil is warm.
- Harvest: Cut when the first petals are just opening; buds that show color open in the vase. Cut often and deadhead to keep plants flowering until frost.
Growing cosmos in your part of the Northwest
The same plant behaves differently on the wet west side, the foggy coast and the dry, colder east side.
West-side valleys
Willamette Valley, Puget Sound, southern Oregon
Cosmos is easy here once the soil warms. Don't feed it too much or it grows tall and floppy.
Coast
Oregon and Washington coast
Cosmos blooms well in cool summers. Wind can topple tall plants.
East of the Cascades
Columbia Basin, Yakima, Boise, Spokane, north Idaho
Cosmos handles heat and dry soil well and blooms all summer.
High desert and mountain towns
Central Oregon, high eastern Oregon valleys, McCall, Salmon
Sow after the last frost. Cosmos blooms from midsummer until frost.
More cosmo varieties
More widely sold picks that do well somewhere in the Northwest. The tag says which part of the Northwest suits each one best.
Sensation Mix
The classic cut-flower cosmos in pink, white and crimson on 4- to 5-foot plants. Stake or net it in windy spots.
Both sides
Double Click
Ruffled, layered flowers that look like small dahlias. Excellent in bouquets.
Both sides
Sonata
Compact plants about 2 feet tall for borders and containers, with full-size flowers.
Both sides
Bright Lights
Fiery orange, gold and yellow flowers that handle heat and dry soil, good for hot eastern gardens.
East side
How much to grow
How many to plant
A short row of 10 to 15 plants keeps a vase full all summer.
In the vase
Cut cosmos last about five to seven days in the vase.
Key numbers
- 65–85°FSoil to sprout
- 60–80Days to bloom
- 1–6 ft by varietyHeight
- FloppingBiggest risk
Top care tip: Skip the fertilizer and deadhead often; lean soil and regular cutting give the most flowers.
Growing notes
What makes the difference in Northwest gardens, in plain language.
Easy from seed
Cosmos are summer annuals from Mexico, with feathery leaves and daisy-like flowers in pink, white, magenta and orange. They sprout fast in warm soil and bloom from midsummer until frost.
Sow seeds directly once the soil warms, or start them indoors four to six weeks earlier in short-season areas like Central Oregon and transplant after your last frost.
Lean soil, more flowers
Cosmos flower best in average or poor soil. Rich soil and fertilizer make tall, leafy plants with fewer blooms. Water seedlings until they're established; after that, they handle dry spells well.
Pinch the growing tip when plants are about a foot tall to make them branch. Tall types like Sensation reach 4 to 6 feet and need staking or netting in windy or rainy spots.
Cutting and deadheading
For bouquets, cut stems when the flowers are just opening, early in the morning. They last about a week in water.
Deadhead regularly to keep new flowers coming. Late in the season, let some flowers go to seed: finches eat the seeds, and plants often reseed for next year.
Good neighbors
Good neighbors
- Vegetable beds. The open flowers feed hoverflies and parasitic wasps that eat aphids and caterpillars.
Pests and problems
What most often goes wrong with cosmos in Northwest gardens, how to spot it and what to do.
Flopping
Signs: Tall plants fall after rain.
What to do: Pinch young plants and stake.
Too much leaf
Signs: Big plants with few flowers.
What to do: Skip the fertilizer; cosmos flowers best in lean soil.
Saving cosmo seed
Will it come true?
Cosmos varieties cross with each other, so saved seed gives a mix of colors. Many gardeners enjoy the surprise.
How to save it
Collect the long, dark seeds once they turn dark and dry on the plant. Store dry seed in a labeled paper envelope in a cool, dry place.
Common questions about growing cosmos
When should I plant cosmos in Oregon, Washington and Idaho?
Plant in the garden: May 10 – Jun 21 in Portland and Seattle, May 15 – Jun 26 in Spokane, May 1 – Jun 12 in Boise and Jun 16 – Jul 28 in Bend. Pick your town at the top of the page for your own dates.
Why are my cosmos all leaves and no flowers?
Too much fertilizer or rich soil. Cosmos bloom best in lean soil. Stop feeding, and plant next year's in a less fertile spot.
Do cosmos come back every year?
They're annuals, killed by frost, but they often reseed if you let some flowers drop seed.
When should I plant cosmos in the Northwest?
Sow outdoors after the soil warms, usually late May on the west side. Where summers are short, start seeds indoors in April and transplant after the last frost.
See what else to plant in March, April, May or June.
Dahlias
Sunflowers
Zinnias
Sweet peas
Tulips
Daffodils
Peonies
Nasturtiums
Marigolds
Calendula
Snapdragons
Ranunculus