Brussels Sprouts in Zone 6A — Pacific Northwest

Brussels sprouts are a rewarding crop to grow in the Pacific Northwest. Their unique, nutty flavor is enhanced by our cool nights, and they add a touch of elegance to any meal. Plus, there's something deeply satisfying about harvesting those little cabbages you grew yourself during our long, mild fall.

We do face some challenges in our region, like cool soil in the spring and a relatively short window for warm-season crops. However, with careful timing and a little attention, you can easily enjoy a successful Brussels sprouts harvest within our 148-day growing season.

Starting Brussels sprouts indoors gives you a head start on our sometimes-slow springs. Begin sowing seeds from late March through mid April, roughly six weeks before you plan to transplant them outdoors. This allows you to get ahead of the cool soil temperatures that can hinder early growth.

Use seed trays or small pots filled with a good seed-starting mix. Provide consistent warmth (around 70°F) and plenty of light – a grow light is beneficial, especially with our overcast spring days. Water gently from the bottom to avoid damping off and encourage strong root development.

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

Space your plants 18-24 inches apart to allow for proper air circulation and growth. Our mild summers are generally kind to Brussels sprouts, but be mindful of potential late frosts and protect young plants if necessary.

Brussels sprouts need consistent moisture to develop those tight, flavorful sprouts we love. In the Pacific Northwest's dry summer months, regular watering is essential, but it's easy to overdo it, especially in our wet springs. Aim for a "just right" approach.

During our dry summer, check the soil moisture by sticking your finger about two inches deep. If it feels dry, it's time to water. Generally, aim for about 1-1.5 inches of water per week, delivered at the base of the plants to avoid wetting the foliage excessively. Given our dry-summer humidity, overhead watering isn't a major concern, but basal watering is still best.

Pay attention to your plants: drooping leaves indicate underwatering, while yellowing leaves and soggy soil suggest overwatering. A layer of mulch, like straw or compost, will help retain moisture and regulate soil temperature, which is especially helpful during our occasional heat spikes.

Brussels sprouts can grow quite tall and become top-heavy, especially when those sprouts start to plump up. A good staking system will prevent them from toppling over in our sometimes-windy conditions. Bamboo stakes or sturdy tomato cages work well.

Install your chosen support system when the plants are about two feet tall. Gently tie the main stalk to the stake at several points as it grows, using soft twine or plant ties. This will provide the necessary support without damaging the plant.

Pruning Brussels sprouts is minimal but important for maximizing your harvest. As the sprouts develop from the bottom up, remove the yellowing or damaged lower leaves. This improves air circulation and directs the plant's energy towards sprout production.

About 3-4 weeks before your expected harvest, top the plant by cutting off the top growth above the uppermost sprouts. This further encourages the sprouts to mature and develop a richer flavor. As our first frost approaches around early October, you can remove any remaining leaves to focus the plant's energy on the remaining sprouts.

You can expect your first Brussels sprouts harvest from early August through mid September, depending on when you transplanted. The sprouts are ready to harvest when they are firm, tight, and about 1-2 inches in diameter. Start harvesting from the bottom of the stalk and work your way up.

To harvest, simply twist or snap off the sprouts where they join the stalk. Removing the lower leaves as you harvest will make the process easier. Brussels sprouts actually improve in flavor after a light frost, so don't be afraid to leave them on the plant a bit longer as the weather cools.

Even after a frost, you can continue to harvest sprouts as needed. If a hard freeze is predicted, you can harvest the entire stalk and store it in a cool, dry place or even stand the cut stalk in a bucket of water in a protected area.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and undersides of leaves. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects. Populations can explode in warm weather. Ants may farm them.
• How to fix/prevent it: Strong water spray. Encourage ladybugs and lacewings. Insecticidal soap for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer.

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in leaves. Dark green droppings. White butterflies hovering.
• What causes it: Larvae of white cabbage butterflies. Multiple generations per season if our mild summers are warm.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent egg laying. Handpick caterpillars. Interplant with aromatic herbs. Encourage parasitic wasps.

Loose Sprouts from Heat

• What it looks like: Sprouts that are not tightly closed and feel soft. May taste bitter.
• What causes it: Periods of hot weather, especially if combined with inconsistent watering. Our mild summers usually prevent this problem, but heat spikes can occur.
• How to fix/prevent it: Provide consistent watering, especially during hot spells. Mulch to regulate soil temperature. Choose heat-tolerant varieties if heat is a consistent issue in your garden.

Clubroot

• What it looks like: Stunted growth, wilting in afternoon heat, yellowing leaves. Roots are swollen, distorted, and club-shaped.
• 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 heat and dry-summer rainfall help minimize some common problems. Late blight is less of a concern for Brussels sprouts than for tomatoes, but good air circulation is still beneficial. Slugs can be a problem for young plants, so use slug bait or other control methods. Cool soil in spring can delay growth, so starting indoors is highly recommended.

Brussels sprouts benefit from companion planting in the Pacific Northwest. Green beans fix nitrogen in the soil, supporting the growth of your Brussels sprouts. Celery repels cabbage white butterflies, reducing the risk of cabbage worms. Onions and dill also deter pests, keeping your plants healthy. Potatoes are good neighbors too, as they don't compete for the same nutrients.

Avoid planting Brussels sprouts near tomatoes, strawberries, or peppers. Tomatoes and peppers can attract pests that also affect Brussels sprouts. Strawberries compete for nutrients and can harbor diseases that may spread to your brassicas.