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A tall sunflower in bloom against a blue sky
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When to plant sunflowers in Hillsboro and Beaverton, OR

Plant sunflowers from seed, directly in the garden in Hillsboro and Beaverton, May 10 – Jun 21.

Easy Plant seeds in the ground

Difficulty
Easy
Sun
Full sun
Spacing
6 inches (small types) to 24 inches (giants) apart
Planting depth
1 inch deep
Frost
Killed by frost
Flowers
Blooms about 60 to 90 days after sowing

Why these dates

Hillsboro and Beaverton's typical last spring frost is April 16. Frost kills sunflowers, 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 sunflowers in Hillsboro and Beaverton

  1. Prepare the bed: loosen the soil and mix in an inch or two of compost.
  2. Plant seeds May 10 – Jun 21, 1 inch deep, 6 inches (small types) to 24 inches (giants) apart.
  3. Keep the soil evenly moist until sprouts appear, which can take one to three weeks in cool soil.
  4. Harvest: Cut flowers when the petals are just opening. For seeds, let heads dry on the plant until the back turns brown, and cover them from birds.

Key numbers

Growing notes

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

Timing and sowing

Sunflowers sprout fastest in warm soil, so sow after the soil has warmed in late spring. In cold, wet soil, seeds sit for days and seedlings get eaten before they grow. Sow directly where they'll grow, since their long taproot makes transplanting hard.

For a steady supply of cut flowers, sow a short row every two weeks into early July. Single-stem cutting varieties like ProCut bloom once, then they're done, so succession sowing keeps flowers coming. Branching types bloom over a longer stretch.

Wind, soil and support

Sunflowers aren't fussy about soil as long as it drains, but giants like Mammoth Grey Stripe need extra compost and steady water to reach full height. They also catch a lot of wind. Plant tall varieties in a sheltered spot, mound soil around the base of the stems as they grow, and stake them before late-summer storms.

Dwarf types like Teddy Bear are a good choice for windy sites and containers.

Harvesting seeds

For seeds, the head is ready when the back turns from green to yellow-brown and the petals have dropped. Birds and squirrels know before you do, so cover heads with paper bags or mesh once seeds start to fill. Cut the head with a foot of stem and hang it in a dry, airy place to finish. West of the Cascades, fall rain can mold heads left outside, so bring them in early.

Common questions

When is the last frost in Hillsboro and Beaverton, OR?

Typically April 16. In 9 years out of 10, frost is over by May 3. These are 1991–2020 NOAA climate normals for Portland-Hillsboro Airport.

Is it too late to plant sunflowers in Hillsboro and Beaverton?

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 October 23.

When do sunflowers bloom?

Blooms about 60 to 90 days after sowing. Cut flowers when the petals are just opening. For seeds, let heads dry on the plant until the back turns brown, and cover them from birds.

Do sunflowers really follow the sun?

Young plants do: their buds and leaves turn from east to west during the day and reset overnight. Once the flowers open, most mature heads stop moving and stay facing roughly east.

Why are my sunflower heads empty of seeds?

Poor pollination is the usual cause, from too few bees or cool, wet weather at bloom. Some cutting varieties like ProCut are bred to be pollenless so they don't shed on tables, and they make few seeds.

Can I transplant sunflower seedlings?

It's possible if you move them very young and keep the root ball intact, but they often stall. Sowing directly in the garden usually gives stronger, faster plants.

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Full planting calendar for Hillsboro and Beaverton · Sunflowers in every city