Cabbage in Zone 7B — Northern California

Cabbage is a rewarding crop to grow in Northern California. Its crisp texture and mild flavor make it a versatile addition to slaws, stir-fries, and more. The satisfaction of harvesting a tightly packed head of cabbage that *you* grew, especially with our long growing season, is tough to beat.

While we face challenges like drought and water restrictions in our Mediterranean climate, starting cabbage indoors and timing your planting right allows you to harvest before the peak of summer heat. With our 245-day growing season, you can enjoy homegrown cabbage in spring and fall.

To get a head start on your spring cabbage crop, start seeds indoors from mid January through early February. This gives the seedlings about 6 weeks to develop before transplanting. Use seed trays or small pots filled with a good seed-starting mix.

Keep the trays consistently moist – bottom watering works great to avoid disturbing the tiny seedlings. Place the trays in a warm location, ideally around 70°F, and provide plenty of light. Our early spring warmth can fool you, so indoor starting gives you more control.

Transplant your cabbage seedlings outdoors in early to late March, once they have a few sets of true leaves and the weather has settled a bit. Be sure to harden them off for about a week before planting. Gradually expose them to outdoor conditions to avoid shocking them.

Space the seedlings 12-18 inches apart in rows. Keep an eye on the weather forecast around transplant time. We can still get some unexpected chilly nights, so be prepared to cover the seedlings if necessary.

Cabbage needs consistent moisture to form dense, healthy heads. In our dry Northern California climate, especially during the summer, regular watering is essential. The "finger test" is your friend: stick your finger into the soil about 2 inches deep. If it feels dry, it's time to water.

Aim for about 1-1.5 inches of water per week, depending on rainfall and temperature. Water deeply at the base of the plants to encourage strong root growth and minimize leaf wetness in our low-humidity environment. Overhead watering is okay, but try to water early in the day so the leaves can dry before nightfall.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to root rot, indicated by yellowing leaves and stunted growth. A layer of mulch around your cabbage plants helps retain moisture and suppress weeds—straw or wood chips work well in our region.

You can expect your first cabbage harvest from early May through late June, about 70 days after transplanting. The key is to check the firmness of the head. When you squeeze it gently, it should feel solid and dense.

Harvest when the head has reached its full size for the variety you're growing. Use a sharp knife to cut the head at the base of the plant. Leave the lower leaves intact; they may produce smaller side shoots later.

As our first frost approaches in mid- November, harvest any remaining cabbage heads, even if they aren't quite as large as you'd hoped. They'll store well in a cool, dry place for several weeks.

Here are some common problems you might encounter growing cabbage in Northern California:

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in leaves, leaving dark green droppings. You'll also see white butterflies fluttering around.
• What causes it: The larvae of white cabbage butterflies. They can have multiple generations in our long, warm growing season.
• How to fix/prevent it: Bt spray is very effective. Use floating row covers to prevent butterflies from laying eggs. Handpick caterpillars when you see them. Interplant with aromatic herbs like thyme and sage.

Cabbage Loopers

• What it looks like: Similar to cabbage worms, but these are pale green caterpillars that move in a looping motion. They also chew holes in leaves.
• What causes it: These are the larvae of moths. Like cabbage worms, they thrive in our warm climate.
• How to fix/prevent it: Bt spray is also effective against cabbage loopers. Handpicking, row covers, and attracting beneficial insects can help.

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 expand too quickly, leading to splitting. Common in our dry-summer climate.
• How to fix/prevent it: Water consistently, especially during head formation. Mulch to retain moisture. Harvest promptly when the head is mature to prevent splitting.

Clubroot

• What it looks like: Stunted growth, wilting in the afternoon heat, and yellowing leaves. When you dig up the plant, the roots are swollen, distorted, and club-shaped.
• 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. Improve drainage. Rotate brassicas on a 7-year cycle. Remove and destroy infected plants (don't compost). Start transplants in sterile mix.

Northern California Specific Challenges: Our moderate-to-hot summers and dry conditions can stress cabbage plants, making them more susceptible to pests and diseases. Consistent watering and monitoring for problems are key to success. Our microclimates can also impact growth, so pay attention to your specific area's conditions.

Companion planting can help your cabbage thrive in Northern California. Green beans are good companions because they fix nitrogen in the soil, which benefits cabbage. Celery can deter cabbage white butterflies. Onions and dill can also repel pests. Potatoes are said to improve the overall health of cabbage plants.

Avoid planting cabbage near tomatoes, strawberries, or peppers. These plants can attract similar pests and diseases, increasing the risk of problems. They may also compete for nutrients in the soil.