Brussels Sprouts in Zone 6A — Mountain West

Brussels sprouts, with their nutty, slightly sweet flavor, are a real treat when you grow them yourself. The cool nights we get even in summer here in the Mountain West actually enhance their flavor, making them far superior to anything you'll find in the grocery store. Plus, the satisfaction of harvesting those little cabbages after nurturing them through our unique growing season is hard to beat.

High altitude gardening definitely comes with its challenges, including intense UV, alkaline soil, and a short growing season of only around 153 days. But with careful timing and a few tricks, you can absolutely enjoy a bountiful harvest of Brussels sprouts right here in Zone 6A.

Starting Brussels sprouts indoors gives you a crucial head start in our short Mountain West growing season. Begin your seeds indoors from mid-March through early April, about six weeks before you plan to transplant them outdoors. Use seed trays or small pots filled with a good seed-starting mix, and keep them in a warm location, ideally around 70-75°F, until germination.

Once the seedlings emerge, provide plenty of light – a grow light works wonders, especially with our intense sun. Water from the bottom by placing the tray in a shallow dish of water for a few minutes, preventing damping-off. Remember, spring here can be late in arriving, so patience is key!

Transplant your Brussels sprouts seedlings outdoors in 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. Start with a few hours of shade and increase the time and sun exposure each day.

Plant your seedlings 18-24 inches apart in rows. Even in May, be prepared for unexpected cold snaps or even late-season snow; have frost blankets ready to protect your young plants if needed.

Consistent watering is critical for Brussels sprouts, especially in our dry Mountain West climate. They need moderate moisture to develop those tight, flavorful sprouts. Drought stress can lead to loose, bitter sprouts.

During the heat of summer, check the soil moisture regularly using the "finger test" – stick your finger about two inches deep into the soil. If it feels dry, it's time to water. Aim for about 1-1.5 inches of water per week, watering deeply at the base of the plants rather than overhead to minimize water loss from evaporation in our low humidity.

Signs of underwatering include wilting leaves and stunted growth. Overwatering, on the other hand, can lead to yellowing leaves and root rot. A layer of organic mulch, like shredded bark or straw, can help retain soil moisture and regulate soil temperature, which is especially helpful with our intense sun.

Brussels sprouts grow tall and can become top-heavy, especially when those sprouts start forming. In our windy Mountain climate, staking is essential to prevent them from toppling over.

The best support is a sturdy stake, like a bamboo cane or metal post, driven into the ground near the base of the plant. Install the stake when the plants are young, around 2 feet tall, to avoid damaging the roots later. As the plant grows, gently tie the stalk to the stake with soft twine or plant ties, providing support without constricting growth.

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 to improve air circulation and direct the plant's energy towards sprout production.

About 3-4 weeks before your expected harvest, top the plant by cutting off the top set of leaves. This redirects the plant's energy into the existing sprouts, encouraging them to mature and develop a richer flavor. Keep an eye on the weather as fall approaches. With our first frost around early October, you may need to harvest early if a hard freeze is predicted.

You can expect your first harvest of Brussels sprouts from late July through early September, depending on when you transplanted them. Look for firm, tight sprouts that are about 1-2 inches in diameter. Harvest the sprouts from the bottom of the plant upwards, twisting them off the stem carefully to avoid damaging the plant.

The flavor of Brussels sprouts actually improves after a frost, becoming sweeter and more complex. If possible, leave them on the plant until after a light frost for the best taste. Even though our growing season is short, Brussels sprouts can handle a frost!

As the first hard frost approaches in early October, harvest any remaining sprouts, even if they're small. They'll still be delicious roasted or sautéed.

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

• 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 are open and leafy instead of tightly closed. Bitter taste.
• What causes it: High temperatures, especially during sprout formation.
• How to fix/prevent it: Provide consistent moisture. Use shade cloth 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 intense sun can stress plants, making them more susceptible to pests and diseases. The dry air means you need to be vigilant about watering. Even with moderate summer heat at altitude, those cool nights can lead to temperature swings, so watch the weather forecast and protect your plants when needed.

Good companion plants for Brussels sprouts include green beans, celery, onions, and potatoes. Green beans fix nitrogen in the soil, benefiting the Brussels sprouts. Celery repels cabbage white butterflies. Onions deter many pests, and potatoes help to break up the soil, improving drainage. Dill also makes a great companion because it attracts beneficial insects that prey on cabbage worms and aphids.

Avoid planting Brussels sprouts near tomatoes, strawberries, and peppers. Tomatoes and peppers are heavy feeders and can compete for nutrients. Strawberries can attract pests that also affect Brussels sprouts. These companions may also stunt growth and spread disease.