Cabbage in Zone 9B — Southern California

Cabbage is a rewarding crop to grow in Southern California's Zone 9B, offering a fresh, homegrown taste that beats anything you'll find at the market. Imagine crisp, flavorful cabbage in your slaws and stir-fries, all thanks to our long growing season and mild winters. The satisfaction of harvesting a beautiful head of cabbage that you nurtured yourself is hard to top.

While we face challenges like drought and the occasional heat wave here in SoCal, our 334-day growing season gives us plenty of opportunity to time our cabbage crops perfectly. By starting seeds indoors and transplanting at the right time, you can enjoy a bountiful harvest.

Starting your cabbage indoors gives you a head start on the season, especially important with our very-early spring. Begin sowing your cabbage seeds from late November through mid December, roughly six weeks before you plan to transplant them outdoors. Use seed trays or small pots filled with a good seed-starting mix.

Keep the trays in a warm location, around 70-75°F, until the seeds germinate. A heat mat can be helpful. Provide plenty of light, either from a sunny window or a grow light, once the seedlings emerge. Bottom watering is a great way to keep the soil consistently moist without disturbing the delicate seedlings.

Transplant your cabbage seedlings outdoors from mid January through early February. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and temperature changes.

Choose a sunny spot in your garden and space the seedlings 12-18 inches apart. Even though our winters are mild, be mindful of any late cold snaps that could stress young plants. If a frost is predicted, cover the seedlings with horticultural fleece or cloches.

Cabbage needs consistent moisture to thrive, but overwatering can be just as detrimental, especially with our winter-wet rainfall patterns. Aim to keep the soil evenly moist, but not soggy. In the cooler months, you might only need to water once or twice a week, but as the weather warms up, especially with our hot summer heat inland, increase watering to two or three times a week.

Use the finger test to check the soil moisture – if the top two inches feel dry, it's time to water. Generally, cabbage needs about 1-1.5 inches of water per week, depending on weather conditions. Water at the base of the plant to avoid wetting the leaves, which can encourage fungal diseases in our low-to-moderate humidity.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. Mulching around your cabbage plants with straw or wood chips helps retain moisture in the soil and keeps the roots cool during the summer heat.

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

Harvest when the head has reached its full size for the variety you're growing. Use a sharp knife to cut the head off at the base of the plant, leaving a few outer leaves attached.

As late December approaches and our first frost is on the horizon, harvest any remaining heads, even if they're not quite fully mature. Smaller cabbages can still be used in cooking.

Here are some common issues you might encounter growing cabbage in Southern California:

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 our warm climate.
• 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.

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: These are also larvae of a moth. They thrive in warm weather.
• How to fix/prevent it: Use Bt spray, handpick, and encourage beneficial insects like parasitic wasps. Row covers can help.

Splitting

• What it looks like: The cabbage head cracks open.
• What causes it: Inconsistent watering. Heavy watering after a dry spell causes the head to expand too quickly.
• How to fix/prevent it: Water regularly and consistently. Mulch to retain moisture. Harvest mature heads promptly 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: 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.

Southern California Specific Challenges: Our hot summer heat inland can stress cabbage plants, making them more susceptible to pests and diseases. Consistent watering is crucial to prevent splitting, but during periods of water restrictions, you may need to prioritize watering cabbage over other less water-dependent crops. The Santa Ana winds can also dry out the soil quickly, so keep a close eye on moisture levels.

Companion planting can help your cabbage thrive. Green beans are a great companion because they fix nitrogen in the soil, which cabbage needs. Celery helps to deter cabbage white butterflies, reducing the risk of cabbage worms. Onions also deter pests and can help prevent fungal diseases. Potatoes are said to improve the flavor of cabbage. Dill attracts beneficial insects that prey on cabbage pests.

Avoid planting cabbage near tomatoes, strawberries, or peppers. Tomatoes and peppers compete for nutrients and can attract some of the same pests. Strawberries can inhibit cabbage growth.