Brussels Sprouts in Zone 6B — Mountain West

Brussels sprouts, with their nutty flavor that sweetens after a touch of frost, are a real treat in our Mountain gardens. The cool nights even in summer help develop their unique taste, and the satisfaction of harvesting your own sprouts as the fall colors appear is hard to beat.

Our high altitude, intense sun, and short growing season present challenges, but with careful timing, you can absolutely grow delicious Brussels sprouts here. Our 163-day growing season means starting early, but the reward is well worth it.

To get a jump start on our short season, start your Brussels sprouts indoors in early to late March. This gives them about 6 weeks to get a head start before transplanting. Use seed trays or small pots with a good quality seed starting mix.

Keep the soil consistently moist, and provide plenty of light – a sunny windowsill or grow lights work well. I like to bottom water my seedlings to encourage strong root growth. Remember that the late spring can be tricky here, so starting indoors gives us the best chance of a good harvest.

Transplant your Brussels sprouts outdoors in late April through mid May, after 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 helps them adjust to the intense sun and cooler temperatures.

Space the plants 18-24 inches apart to allow for good air circulation and plenty of room to grow. Even though we are past our last frost date, keep an eye on the weather forecast. We can still get some late cold snaps, so be ready to cover your young plants if needed.

Brussels sprouts need consistent moisture to produce those tight, delicious sprouts we're after. In our dry Mountain climate, regular watering is essential. A lack of water can lead to loose, bitter sprouts, and nobody wants that!

During the heat of summer, aim to water deeply about 1-2 inches per week, depending on rainfall. Stick your finger about two inches into the soil – if it feels dry, it's time to water. It's best to water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in some areas, but our low humidity usually keeps that in check.

Pay attention to your plants! Drooping leaves can indicate underwatering, while yellowing leaves may suggest overwatering. A good layer of mulch around the base of the plants will help retain moisture and keep the soil cool, which is especially helpful during our intense summer sun.

Brussels sprouts can get quite tall and top-heavy, especially when those sprouts start forming. In our windy Mountain climate, staking them is a good idea to prevent them from toppling over.

I find that sturdy stakes, like bamboo or metal, work best. Install them when the plants reach about 2 feet tall. Gently tie the main stem to the stake with soft twine or plant ties, making sure not to constrict the stem's growth.

Pruning Brussels sprouts is pretty straightforward. As the sprouts develop up the stem, remove the yellowing or damaged lower leaves. This helps improve air circulation and directs the plant's energy towards sprout production.

About 3-4 weeks before your expected harvest, you can top the plant by cutting off the top cluster of leaves. This encourages the plant to focus its energy on ripening the existing sprouts. With our first frost around early October, keeping an eye on the calendar for this step is important.

Here in Zone 6B of the Mountain West, you can expect your first Brussels sprouts harvest in 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 plant upwards.

To harvest, simply twist or snap off the sprouts from the stem. Don't pull, or you may damage the plant. After a light frost, the flavor of the sprouts intensifies, so try to leave some on the plant as long as possible.

Brussels sprouts produce continuously, so you can harvest over several weeks. As the first frost approaches, harvest any remaining sprouts that are close to maturity. Even smaller sprouts will taste great roasted or sautéed.

Here are some common problems you might encounter with Brussels sprouts in our Mountain gardens:

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects. Populations explode during warm weather. Ants may farm them.
• How to fix/prevent it: Strong water spray to knock them off. 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 holes in leaves. Dark green droppings. White butterflies hovering around plants.
• What causes it: Larvae of white cabbage butterflies. Multiple generations per season in warmer weather.
• 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 formed, but rather loose and leafy. They may also taste bitter.
• What causes it: High temperatures stress the plants, preventing proper sprout formation. This is more common during heat waves.
• How to fix/prevent it: Provide consistent moisture, especially during hot spells. Mulch around the base of the plants to keep the soil cool. Consider providing shade during the hottest part of the day. 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.

Mountain West Specific Challenges: Our moderate-at-altitude heat coupled with low humidity can sometimes lead to inconsistent sprout formation. Consistent watering is key. The dry climate also means pests like aphids can become a problem quickly, so stay vigilant. Our alkaline soil can contribute to nutrient deficiencies, so amend your soil with compost regularly.

Companion planting can really help your Brussels sprouts thrive. Green beans are great companions because they fix nitrogen in the soil, which Brussels sprouts love. Celery helps repel cabbage white butterflies, reducing cabbage worm infestations. Onions and dill also deter pests, while potatoes don't compete for the same nutrients.

Avoid planting tomatoes, strawberries, or peppers near your Brussels sprouts. Tomatoes and peppers are susceptible to similar diseases, and strawberries can attract pests that will also bother your sprouts.