Cabbage in Zone 9A — Northern California

Cabbage is a rewarding crop to grow in Northern California. The heads offer a crisp, slightly sweet flavor that's far superior to store-bought versions. Fresh cabbage shines in slaws, stir-fries, or even a simple side dish of braised cabbage with bacon. Plus, the long growing season and mild winters in our Mediterranean climate allow you to enjoy multiple harvests.

While we face challenges like drought and the occasional heat spike, careful planning and water-wise gardening techniques allow you to successfully grow cabbage. Our 288-day growing season gives you plenty of leeway to work around any unexpected temperature swings.

To get a head start on your spring cabbage crop, start seeds indoors from mid December through early January. This gives your seedlings about 6 weeks to develop before transplanting. You'll need seed trays or small pots, a good quality seed-starting mix, and a warm, bright location.

A heat mat can help speed up germination. Once the seedlings emerge, provide plenty of light with a grow light or place them in a south-facing window. Don't forget to water gently from the bottom to avoid damping off. Our early springs here in Northern California mean you can get these seedlings out relatively early, so plan accordingly.

Transplant your cabbage seedlings outdoors from early February through early March. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the cooler temperatures and stronger sunlight.

Choose a sunny spot with well-drained soil and space the plants 12-18 inches apart. Even though it's still relatively mild in February, keep an eye on the forecast for any late frosts and be prepared to cover your seedlings if necessary.

Cabbage needs consistent moisture to thrive, but avoid overwatering, especially with our dry summers. Aim to keep the soil evenly moist, but not waterlogged. During the cooler months, you may only need to water once or twice a week, but as the weather warms up, increase the frequency.

Check the soil moisture by sticking your finger about 2 inches deep. If it feels dry, it's time to water. Generally, cabbage needs about 1-1.5 inches of water per week, depending on the weather. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our low-humidity environment.

Wilting leaves are a sign of underwatering, while yellowing leaves and stunted growth can indicate overwatering. Applying a layer of mulch around your cabbage plants helps retain moisture and suppress weeds.

You can expect your first harvest of cabbage from mid April through early June, about 70 days after transplanting. The best way to tell if a cabbage head is ready to harvest is to give it a gentle squeeze. It should feel firm and solid.

Also, consider the expected size of the variety you are growing. Once the head reaches full size and feels firm, use a sharp knife to cut the stem at the base of the plant. As our first frosts usually arrive in early December, harvest any remaining cabbage heads before then to prevent frost damage.

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

Cabbage Worms

• What it looks like: Smooth green caterpillars munching on leaves, leaving irregular holes. You might also see dark green droppings and white butterflies fluttering nearby.
• What causes it: These are the larvae of white cabbage butterflies, which can have multiple generations in our long, warm growing season.
• How to fix/prevent it: Bt spray is very effective. Floating row covers are great for preventing the butterflies from laying eggs in the first place. You can also handpick the caterpillars or interplant with aromatic herbs like thyme and sage to deter them.

Cabbage Loopers

• What it looks like: Pale green caterpillars that move in a looping motion. They chew large holes in leaves, often leaving the veins intact.
• What causes it: Similar to cabbage worms, these are the larvae of moths. They thrive in our moderate-to-hot summer temperatures.
• How to fix/prevent it: Bt spray is effective. Handpicking is also an option for smaller infestations. Encourage natural predators like parasitic wasps.

Splitting

• What it looks like: The cabbage head cracks open.
• What causes it: Inconsistent watering, especially heavy watering after a period of drought. Our dry summers followed by occasional heavy rains can make this a common issue.
• How to fix/prevent it: Maintain consistent soil moisture by watering regularly. Use mulch to help retain moisture. Harvest cabbage heads as soon as they are mature to prevent them from 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 that can persist for many years, especially in acidic, wet soil.
• How to fix/prevent it: Raise the 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 them!). Start transplants in sterile mix.

Northern California Specific Challenges: Our moderate-to-hot summers, combined with low humidity and dry-summer rainfall, can stress cabbage plants if watering isn't consistent. Be vigilant about monitoring soil moisture and providing adequate water, especially during heat waves. The microclimates throughout Northern California can also impact growth, so adjust your watering schedule based on your specific location.

Companion planting can help your cabbage thrive. Green beans are great companions because they fix nitrogen in the soil, benefiting the cabbage. Celery can help deter cabbage white butterflies. Onions repel many pests, while potatoes don't compete for the same nutrients. Dill attracts beneficial insects that prey on cabbage pests.

Avoid planting cabbage near tomatoes, strawberries, or peppers. Tomatoes and peppers can stunt the growth of cabbage, while strawberries are susceptible to similar pests and diseases, potentially spreading problems to your cabbage.