Brussels Sprouts in Zone 6B — Pacific Northwest

Brussels sprouts, with their nutty flavor and satisfying texture, are a fantastic addition to the PNW garden. Their cold hardiness means you can harvest them well into our long, mild fall, and the cool nights actually improve their flavor. Plus, there's nothing quite like roasting up homegrown sprouts on a chilly evening.

We do face some challenges here in Zone 6B, like cool soil in spring and the occasional late blight scare. But with a little planning and attention to timing within our 162-day growing season, you can absolutely enjoy a bountiful Brussels sprouts harvest.

Starting Brussels sprouts indoors gives you a head start, crucial for our relatively short summers. Aim to sow seeds indoors from mid-March through early April, about six weeks before you plan to transplant them outside. Use seed trays or small pots filled with a good-quality seed starting mix.

Keep the trays consistently moist by bottom watering – set them in a tray of water and let the soil absorb it from the bottom. This helps prevent damping-off. Place the trays in a warm spot (around 70°F) and provide ample light, especially with our often overcast spring days. A simple shop light works wonders!

Because our spring can be slow to warm up, starting indoors ensures your plants are strong and ready to take off once the weather cooperates. Remember, Brussels sprouts need a long growing season, so this early start is key.

Transplant your Brussels sprouts seedlings outdoors from early to late May, once the danger of hard frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind, preventing transplant shock.

Space the plants 18-24 inches apart in rows. Even though we rarely see temperatures above 90°F, good air circulation is still important. Keep an eye on the weather forecast around transplant time; a late cold snap can still happen.

Brussels sprouts need consistent moisture to develop those tight, delicious sprouts. In our dry-summer climate, you'll need to be more attentive to watering than you might think. Aim for about 1-1.5 inches of water per week, especially during the dry summer months.

The "finger test" is your best friend: stick your finger about 2 inches deep into the soil near the base of the plant. If it feels dry, it's time to water. Water deeply at the base of the plant rather than overhead to minimize the risk of fungal diseases that can thrive even in our dry summers.

Underwatering can lead to loose, bitter sprouts, while overwatering can cause root rot. Watch for signs like yellowing leaves or wilting, and adjust your watering schedule accordingly. A layer of mulch around the base of the plants helps retain moisture and suppress weeds, which is a huge win in our wet springs and dry summers.

Brussels sprouts grow tall, and those stalks can become top-heavy, especially when loaded with sprouts. Add in our occasional strong winds, and you'll see why staking is a good idea.

Individual stakes work well. Insert a sturdy stake near each plant at transplanting time, or when the plants reach about 2 feet tall. As the plant grows, gently tie the stalk to the stake with soft twine, making sure not to constrict the stem.

Pruning Brussels sprouts is pretty straightforward. As the sprouts develop upward along the stalk, remove the yellowing or damaged lower leaves. This improves air circulation and directs the plant's energy to the developing sprouts.

About 3-4 weeks before you plan to harvest, top the plant by cutting off the growing tip. This encourages the plant to put all its energy into the sprouts, resulting in larger, more uniform sprouts. Don't wait too late, though.

As our first frost approaches around early October, you can remove any remaining leaves to help the sprouts mature. The frost will actually sweeten the flavor!

You can expect your first Brussels sprouts harvest from late July through early September, depending on when you transplanted. Look for firm, tight sprouts that are about 1-2 inches in diameter. Start harvesting from the bottom of the stalk upwards, twisting or cutting the sprouts off cleanly.

Harvesting from the bottom up allows the upper sprouts to continue developing. The flavor of Brussels sprouts improves dramatically after a frost, so don't be afraid to leave them on the plant as long as possible into the fall. We often have a long, mild fall here, so take advantage of it!

Even after a light frost, you can continue harvesting. If a hard freeze is predicted, you can harvest the entire stalk and store it in a cool, dry place for a few weeks.

Here are a few common problems you might encounter with Brussels sprouts in the PNW:

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects. Populations explode in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: Strong water spray knocks them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer (it attracts them).

Cabbage Worms

• What it looks like: Smooth green caterpillars on brassica leaves. Irregular holes chewed in leaves. Dark green droppings. White butterflies hovering around plants.
• What causes it: Larvae of white cabbage butterflies. Multiple generations per season in warm climates.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent egg laying. Handpick caterpillars. Interplant with aromatic herbs (thyme, sage). Encourage parasitic wasps.

Loose Sprouts from Heat

• What it looks like: Sprouts that are not tightly formed and compact, but rather loose and leafy. They may also taste bitter.
• What causes it: While we have mild summers, a few days of unseasonably warm weather can stress the plants, especially young ones, leading to loose sprouts.
• How to fix/prevent it: Consistent watering is key. Provide shade during the hottest part of the day with shade cloth. Choose heat-tolerant varieties.

Clubroot

• What it looks like: Stunted growth, wilting in afternoon heat, yellowing leaves. Roots are swollen, distorted, and club-shaped when dug up.
• What causes it: Soil-borne pathogen (Plasmodiophora brassicae) that persists in soil for 10+ years. Favors acidic, wet soil.
• How to fix/prevent it: Raise soil pH to 7.0-7.2 with lime. Improve drainage. Rotate brassicas on a 7-year cycle. Remove and destroy infected plants (don't compost). Start transplants in sterile mix.

Pacific Northwest Specific Challenges: Our mild summers and dry-summer rainfall can actually be beneficial for Brussels sprouts, as they prefer cooler temperatures and don't like overly humid conditions. However, be vigilant about watering during dry spells to prevent loose sprouts. Watch out for late blight, which can sometimes affect brassicas, and take steps to improve soil drainage, especially during our wet springs.

Companion planting can give your Brussels sprouts a boost. Green beans fix nitrogen in the soil, benefiting the sprouts. Celery and onions deter pests, while dill attracts beneficial insects. Potatoes don't directly help the Brussels sprouts, but they don't compete for the same nutrients and can be grown nearby.

Avoid planting Brussels sprouts near tomatoes, strawberries, or peppers. Tomatoes and peppers are susceptible to similar pests and diseases, increasing the risk of problems. Strawberries may inhibit the growth of brassicas.