Cabbage in Zone 4B — Mountain West

Cabbage thrives in our Mountain West gardens, offering a satisfying crunch and a slightly sweet flavor that store-bought versions just can't match. Its versatility in the kitchen is a real boon too, from slaws and stir-fries to hearty soups and stews, perfect for those cool evenings we experience even in the height of summer.

The short 128-day growing season and intense sun at our altitude can present a challenge, but with careful timing and a little extra attention, you can absolutely enjoy a successful cabbage harvest. The key is to get a head start indoors, giving your plants the best possible advantage.

Starting cabbage indoors is the way to go for spring harvests in our short-season climate. You'll want to sow your seeds mid-March through early April, roughly six weeks before you plan to transplant them outside. This gives them a good head start before our last frost, which often lingers until mid-May.

Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist, and consider bottom watering to avoid damping off. Place the trays under grow lights or in a very sunny window; remember, our intense sun even indoors can be beneficial. Aim for a consistent temperature around 70°F to encourage germination, which can be tricky with our late-spring temperature swings.

Transplanting your cabbage seedlings outdoors should happen early to late May, once the danger of hard frost has passed. Before you put them in the ground, harden them off by gradually exposing them to outdoor conditions for about a week. This is crucial to prevent shock from our intense UV.

Space your cabbage plants 12-18 inches apart in rows. Choose a spot that gets full sun – at least 6-8 hours a day. Even though our summers aren't scorching, cabbage still needs plenty of light to develop those tight heads. Be prepared for late-season cold snaps by having row covers ready.

Cabbage needs consistent moisture to thrive, but overwatering can be just as detrimental, especially in our alkaline soil. The goal is to keep the soil evenly moist, not soggy. Since our rainfall is low and humidity is even lower, you'll need to be diligent about watering.

During the warmer months, check the soil moisture by sticking your finger about two inches deep. If it feels dry, it's time to water. Aim for about 1-1.5 inches of water per week, delivered deeply at the base of the plants to avoid wetting the leaves and promoting fungal diseases, which are less of a concern in our dry climate but still possible.

Watch for signs of underwatering, like wilting leaves, or overwatering, like yellowing leaves. Splitting heads are a sign of inconsistent watering, often caused by heavy watering after a dry spell. Mulching around your cabbage plants with straw or wood chips can help retain moisture and regulate soil temperature, which is especially helpful with our cool nights.

You can expect your first cabbage harvest from early July through late August, about 70 days after transplanting. The key is to watch for signs of maturity, not just go by the calendar.

A ripe cabbage head will feel firm and solid when you gently squeeze it. It should also be close to the full size expected for the variety you're growing. To harvest, use a sharp knife to cut the head off at the base of the plant.

As mid-September approaches and the threat of frost looms, harvest any remaining mature heads, even if they're not quite as large as you'd hoped. They won't ripen further off the plant. Cabbage can tolerate a light frost, but a hard freeze will damage the heads.

Here are some common problems you might encounter growing cabbage in the Mountain West:

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in leaves, leaving dark green droppings. You might also see white butterflies fluttering around.
• What causes it: Larvae of white cabbage butterflies. The intense sun can actually help suppress populations compared to more humid climates, but they can still be a nuisance.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent butterflies from laying eggs. Handpick caterpillars. Interplant with aromatic herbs like thyme and sage to deter them.

Cabbage Loopers

• What it looks like: Similar to cabbage worms, but these caterpillars move in a looping motion. They also chew holes in leaves.
• What causes it: Another type of caterpillar. Like cabbage worms, they thrive in warm weather, but our cool nights can slow their development.
• How to fix/prevent it: Bt spray works well. Handpicking is also effective. Encourage natural predators like parasitic wasps.

Splitting

• What it looks like: The cabbage head cracks open.
• What causes it: Inconsistent watering. A sudden heavy watering after a dry spell causes the head to grow too quickly, leading to splitting. This is especially common given our dry summers and sporadic rainfall.
• How to fix/prevent it: Water consistently. Mulch around plants to retain moisture. Harvest heads as soon as they are mature to prevent splitting.

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: A soil-borne pathogen (Plasmodiophora brassicae) that persists in the soil for many years. It favors acidic, wet soil.
• How to fix/prevent it: Raise soil pH to 7.0-7.2 with lime, which is often necessary in our alkaline soils. 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 summer heat and low humidity generally help reduce disease pressure on cabbage. However, the intense sun can stress plants if they're not adequately watered. Hail can also cause significant damage to leaves and heads, so consider using netting if hail is common in your area.

Companion planting can be a great way to improve your cabbage crop. Green beans are good companions because they fix nitrogen in the soil, which cabbage needs. Celery is said to deter cabbage white butterflies, while onions also repel pests. Plant potatoes nearby to help break up the soil, making it easier for cabbage roots to grow. Dill attracts beneficial insects that prey on cabbage pests.

Avoid planting tomatoes, strawberries, or peppers near cabbage. Tomatoes and peppers compete for the same nutrients, and strawberries can attract slugs, which can also damage cabbage.