When to plant Brussels sprouts in Sunnyside, Grandview and Prosser, WA

Start Brussels sprouts from seed indoors Feb 6–20, then plant the young plants in the garden in Sunnyside, Grandview and Prosser Apr 3 – May 15.

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

Sunnyside, Grandview and Prosser's typical last spring frost is May 1. As a cool-season crop that handles light frost, this crop can go in about 4 weeks before that.

Columbia Basin and low eastern valleys. Hot, dry summers and quick spring warm-up. Warm crops go in earlier than west of the Cascades, and irrigation matters more than rain.

How to grow Brussels sprouts in Sunnyside, Grandview and Prosser

Start seeds indoors Feb 6–20 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 Apr 3 – May 15, 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 Sunnyside, Grandview and Prosser, WA?

Typically May 1. In 9 years out of 10, frost is over by May 18. These are 1991–2020 NOAA climate normals for Sunnyside.

Is it too late to plant Brussels sprouts in Sunnyside, Grandview and Prosser?

The spring planting window runs through May 15. Later plantings tend to struggle in summer heat.

When should I start Brussels sprouts from seed indoors in Sunnyside, Grandview and Prosser?

February 6 to February 20, which is 8 to 6 weeks before the April 3 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 Sunnyside, Grandview and Prosser around the same time

Planting dates for Brussels sprouts in nearby areas

Yakima, WA Apr 10 – May 22
Tri-Cities (Pasco, Kennewick, Richland), WA Apr 1 – May 13
Walla Walla, WA Apr 1 – May 13
Moses Lake, WA Apr 1 – May 13
Ellensburg, WA Apr 15 – May 27
Ephrata and Quincy, WA Apr 1 – May 13

Full planting calendar for Sunnyside, Grandview and Prosser · Brussels sprouts in every city