Cabbage in Zone 5B — Mountain West

Cabbage is a fantastic addition to any high-altitude garden. Its crisp, slightly sweet flavor is amplified by our cool nights, making it a versatile ingredient for everything from slaws to hearty soups. Plus, there's real satisfaction in harvesting a dense, healthy head of cabbage that you grew yourself.

Our short growing season and alkaline soil can present challenges for cabbage, but with careful timing and a few key strategies, you can absolutely succeed. Our 149-day growing season is plenty of time to get a spring harvest.

Starting cabbage indoors gives you a head start on our short growing season. Begin your seeds indoors from early to late March, roughly six weeks before you plan to transplant. Use seed trays with a good quality seed starting mix, and keep them in a warm location, around 70°F.

Consistent moisture is key, and bottom watering is a great way to achieve this without disturbing the seedlings. Place the tray in a shallow dish of water and allow the soil to soak it up from the bottom. Remember, spring can be slow to arrive here in the mountains, so be patient! You'll want to give them plenty of light once they sprout, using grow lights if needed.

Transplant your cabbage seedlings outdoors from late April through mid May. Before planting, you'll need to harden them off. This means gradually exposing them to outdoor conditions over about a week. Start with an hour or two of shade, increasing the time and sun exposure each day.

Plant seedlings 12-18 inches apart in well-draining soil. Keep an eye on the weather forecast during this time – late frosts can still happen. Be ready to cover your seedlings if temperatures dip unexpectedly.

Cabbage needs consistent moisture to thrive, but overwatering can lead to problems. In our dry Mountain climate, aim for about 1 inch of water per week, especially during head formation. Use the finger test: stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water.

Water deeply at the base of the plant to encourage strong root growth. Overhead watering can lead to fungal issues, although our low humidity usually prevents this. Signs of underwatering include wilting and stunted growth. Overwatering can cause yellowing leaves and potentially lead to root rot. Mulching around your cabbage plants will help retain moisture and regulate soil temperature in our intense sun.

You can expect your first cabbage harvest from late June through mid August, about 70 days after transplanting. The best indicator of ripeness is a firm, solid head. Gently squeeze the cabbage head; if it feels dense and doesn't give much, it's ready. Also, make sure it's reached full size for the variety you're growing.

To harvest, use a sharp knife to cut the cabbage head at its base. Leave a few outer leaves on the stem; sometimes, smaller heads will develop from these. As our first frost approaches in early October, harvest any remaining cabbage heads, even if they aren't quite fully mature. They can still be used in cooking or pickling.

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 behind. You might also see white butterflies fluttering around your plants.
• What causes it: The larvae of those cabbage butterflies. They can have multiple generations during our relatively short warm season.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent butterflies from laying eggs. Handpick caterpillars when you see them. Planting aromatic herbs like thyme and sage nearby can help deter the butterflies.

Cabbage Loopers

• What it looks like: Pale green caterpillars that move in a looping motion. They chew large, ragged holes in the leaves of your cabbage.
• What causes it: These are the larvae of moths that lay their eggs on your plants.
• How to fix/prevent it: Similar to cabbage worms, Bt spray works well. Handpicking, row covers, and attracting beneficial insects like parasitic wasps are also effective.

Splitting

• What it looks like: The cabbage head cracks open, often after a period of rapid growth.
• What causes it: Inconsistent watering. A sudden heavy watering after a dry spell causes the head to swell too quickly.
• How to fix/prevent it: Consistent watering is key! Use mulch to retain moisture. If heavy rain is predicted, consider harvesting mature heads early.

Clubroot

• What it looks like: Stunted growth, wilting leaves (especially in the afternoon heat), and yellowing. When you dig up the plant, the roots are swollen, distorted, and club-shaped.
• What causes it: A soil-borne pathogen that thrives in acidic, wet soil and can persist for years.
• How to fix/prevent it: Raise the soil pH to 7.0-7.2 with lime. Improve drainage. Rotate your brassicas on a 7-year cycle. Start transplants in sterile potting mix to avoid introducing the pathogen.

Mountain West Specific Challenges: Our intense sun can stress plants, making them more susceptible to pests and diseases. The dry climate means consistent watering is essential. While the low humidity reduces the risk of some fungal diseases, it also means that pests like cabbage worms can thrive.

Companion planting can give your cabbage a boost. Green beans are great companions because they fix nitrogen in the soil, which cabbage loves. Celery can help deter cabbage white butterflies. Onions and dill are also good choices, as their strong scents can confuse pests. Potatoes and cabbage do well together, potatoes help to deter cabbage moths.

Avoid planting cabbage near tomatoes, strawberries, or peppers. Tomatoes can stunt the growth of cabbage, and strawberries and peppers are susceptible to similar soil-borne diseases, which could spread to your cabbage.