Brussels Sprouts in Zone 3A — Mountain West

Brussels sprouts might seem like a gamble with our short growing season, but the taste is worth it. The cool nights we get even in summer concentrate sugars, giving you a sweeter, milder flavor than you'll find in store-bought. Plus, they're incredibly versatile in the kitchen and nothing beats the satisfaction of harvesting your own homegrown sprouts right as the weather turns crisp.

Our high altitude, intense sun, and alkaline soil definitely present challenges for growing Brussels sprouts. But by starting seeds indoors and timing your planting right, you can absolutely enjoy a harvest within our 96-day growing season. Don't let the short season scare you off!

To get a jump start on our short growing season, start your Brussels sprouts indoors from mid-April through early May. This gives you about 6 weeks to get them strong before transplanting. Use seed trays with a good quality seed-starting mix and provide consistent warmth, ideally around 70°F.

Make sure they get plenty of light – a grow light is almost essential here in the Mountain West, especially with our late springs sometimes being overcast. Remember to bottom water your seedlings to encourage strong root growth and prevent damping-off.

Given our cool springs, starting indoors is really the only way to get a decent harvest. Brussels sprouts need a long season, and direct sowing just won't cut it here.

Transplant your Brussels sprouts outdoors around early June, after the risk of 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 nights we experience.

Space your plants 18-24 inches apart to give them plenty of room to grow. Keep an eye on the weather, especially for late frosts or unexpected hail storms, which can set back young transplants. A little row cover protection can go a long way in early June!

Brussels sprouts need consistent moisture to develop those tight, flavorful sprouts. Don't let them dry out, especially during hot spells. In our dry Mountain West climate, that means a regular watering schedule is crucial.

Aim to water deeply about 1-2 inches per week, depending on rainfall. Stick your finger about 2 inches into the soil – if it feels dry, it's time to water. Water at the base of the plants to avoid wetting the leaves, which can encourage disease in other regions, but is less of a concern here with our low humidity.

Underwatering leads to loose, bitter sprouts, while overwatering can cause root rot. Look for yellowing leaves as a sign of overwatering. A good layer of mulch, like straw or wood chips, helps retain moisture and keeps the soil cool, which is especially important with our intense sun.

Brussels sprouts can get tall and top-heavy, especially when those sprouts start forming. The wind can really wreak havoc on them, so staking is a must. Bamboo stakes or sturdy tomato cages work well.

Install your supports when you transplant your seedlings, or soon after, to avoid damaging the roots later on. As the plants grow, gently tie the main stalk to the stake with soft twine or plant tape. This will keep them upright and prevent them from toppling over in our sometimes blustery conditions.

Brussels sprouts don't need a lot of pruning, but a little maintenance can improve your harvest. As the sprouts develop upward along the stalk, remove the yellowing or lower leaves. This improves air circulation and directs the plant's energy towards sprout production.

About 3-4 weeks before your expected harvest in late August or early September, top the plant by cutting off the top cluster of leaves. This forces the plant to focus its energy on maturing the existing sprouts.

Keep an eye on the calendar as we head towards early September. If a hard frost is predicted, you might want to harvest your sprouts, even if they're not quite as big as you'd like.

Here in the Mountain West, you can expect your first Brussels sprouts harvest from late August through mid-September. Look for firm, tight sprouts that are about 1-2 inches in diameter. Harvest from the bottom of the stalk upwards, twisting or cutting the sprouts off cleanly.

Don't be afraid to leave the sprouts on the plant until after the first frost. In fact, the flavor improves dramatically after a frost, as the cold temperatures convert starches to sugars.

Continue harvesting as the sprouts mature, and as early September approaches, consider harvesting the entire stalk if a hard freeze is in the forecast. You can store the entire stalk in a cool, dark place for several weeks, or blanch and freeze the sprouts for later use.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects. Populations can explode during warm days we get in the summer.
• How to fix/prevent it: Strong water spray to knock them off. Encourage ladybugs. Insecticidal soap for heavy infestations.

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing holes in leaves. Dark green droppings. White butterflies fluttering around.
• What causes it: Larvae of white cabbage butterflies. Multiple generations if our short summer stays warm.
• How to fix/prevent it: Bt spray is effective. Floating row covers to prevent egg laying. Handpick caterpillars.

Loose Sprouts from Heat

• What it looks like: Sprouts that don't form tight, compact heads. They're leafy and open.
• What causes it: High temperatures during sprout development. Our moderate-at-altitude summer heat can still stress them.
• How to fix/prevent it: Consistent watering to keep plants cool. Mulch to insulate the soil. Plant varieties that are more heat-tolerant, if available.

Clubroot

• What it looks like: Stunted growth, wilting, yellowing leaves. Swollen, distorted roots when dug up.
• What causes it: Soil-borne pathogen that persists for years. Favors acidic, wet soil.
• How to fix/prevent it: Raise soil pH with lime. Improve drainage. Rotate brassicas on a 7-year cycle. Remove and destroy infected plants.

Mountain West Specific Challenges: Our intense sun can stress plants, making them more susceptible to problems. Low humidity helps prevent some fungal diseases, but consistent watering is crucial. The dry climate means pests like aphids can thrive if not kept in check.

Good companions for Brussels sprouts include green beans, celery, onions, potatoes, and dill. Green beans fix nitrogen in the soil, benefiting the sprouts. Celery repels cabbage white butterflies. Onions and dill deter aphids. Potatoes don't compete for the same nutrients.

Avoid planting Brussels sprouts near tomatoes, strawberries, or peppers. Tomatoes and strawberries are susceptible to verticillium wilt, which can also affect Brussels sprouts. Peppers are heavy feeders and can compete for nutrients.