When to plant Brussels sprouts in St. Helens and Scappoose, OR

Start Brussels sprouts from seed indoors Jan 18 – Feb 1, then plant the young plants in the garden in St. Helens and Scappoose Mar 15 – Apr 26.

Moderate Plant young plants (starts)

Difficulty: Moderate
Sun: Full sun
Spacing: 24 inches apart
Planting depth: Plant starts at the depth they grew in the pot
Frost: Handles light frost
First harvest: About 100 days after planting

Why these dates

St. Helens and Scappoose's typical last spring frost is April 10. As a cool-season crop that handles light frost, this crop doesn't need to wait for that date. In the west-side valleys, though, the soil usually isn't ready to work until about March 15.

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 Brussels sprouts in St. Helens and Scappoose

Start seeds indoors Jan 18 – Feb 1 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 Mar 15 – Apr 26, 24 inches apart. Plant starts at the depth they grew in the pot.
Water deeply once or twice a week rather than a little every day, and mulch once the soil is warm.
Harvest: Pick sprouts from the bottom of the stalk up once they're firm and about an inch across. Frost improves the flavor.

Key numbers

About 100 from plantingDays to harvest
6.0–7.5Soil pH
1–1.5 inches a weekWater
Gray cabbage aphidsBiggest risk

Growing notes

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

Soil and long-season feeding

Brussels sprouts stand in the garden for months, so they need deep, rich soil with plenty of compost and a pH of about 6.0 to 7.5. Feed at planting and side-dress once or twice during summer, but don't overdo the nitrogen late in the season, since that can give loose sprouts. Plants grow tall and top-heavy, so firm the soil well around transplants and stake them in windy spots. Mulch to keep soil evenly moist through the dry Northwest summer.

Timing and topping

Sprouts taste best when they mature in cool fall weather, because frost converts starches into sugars. Plant starts in late spring or early summer so the main harvest comes in fall and winter. About a month before you want to pick, you can pinch out the growing tip at the top of the stalk. This "topping" stops the plant growing taller and sends energy into the sprouts, so they size up more evenly. West of the Cascades, plants keep producing into winter. East of the Cascades, harvest before the deepest cold, though plants handle hard frost well.

Aphids and harvest

Gray cabbage aphids are the main pest. They hide between the sprouts and in leaf folds in late summer, protected by a waxy coating. Spray them off with water every few days, and remove badly infested leaves. Beneficial insects often catch up by fall. Pick sprouts from the bottom up when they are firm and about an inch across, snapping off the yellowing leaves below them as you go. Sprouts keep a week or two in the fridge, or longer if you cut the whole stalk and keep it cool.

Common questions

When is the last frost in St. Helens and Scappoose, OR?

Typically April 10. In 9 years out of 10, frost is over by May 1. These are 1991–2020 NOAA climate normals for Scappoose Industrial Airpark.

Is it too late to plant Brussels sprouts in St. Helens and Scappoose?

The spring planting window runs through April 26. Later plantings tend to struggle in summer heat.

When should I start Brussels sprouts from seed indoors in St. Helens and Scappoose?

January 18 to February 1, which is 8 to 6 weeks before the March 15 planting date. Or buy young plants at a garden center instead.

Why are my Brussels sprouts loose and leafy?

Hot weather while sprouts form, too much late nitrogen, or uneven watering can all cause loose sprouts. Time planting so they mature in cool fall weather. Topping the plant a month before harvest also helps them firm up.

Should I cut the top off my Brussels sprouts?

You can. Pinching out the top growing tip about a month before harvest makes the sprouts mature more evenly. If you prefer a longer harvest over winter, leave the top on.

Do Brussels sprouts need frost?

They don't need it, but a few light frosts make them noticeably sweeter. That's why fall and winter harvests are the best. Mature plants tolerate hard frosts well.

Also plant in St. Helens and Scappoose around the same time

Planting dates for Brussels sprouts in nearby areas

Portland, OR Mar 15 – Apr 26
Gresham, OR Mar 15 – Apr 26
Wilsonville and Canby, OR Mar 15 – Apr 26
Hillsboro and Beaverton, OR Mar 19 – Apr 30
Oregon City and West Linn, OR Mar 15 – Apr 26
Salem, OR Mar 15 – Apr 26

Full planting calendar for St. Helens and Scappoose · Brussels sprouts in every city