Bok Choy in Zone 7B — Northern California

Bok choy is a fantastic addition to any Northern California garden. Its mild, slightly peppery flavor shines in stir-fries, soups, and salads, and it's surprisingly easy to grow in our Mediterranean climate. Plus, with our long growing season, you can often get multiple harvests from spring through fall.

While NorCal can throw us some curveballs with drought and occasional heat spikes, bok choy is manageable with careful timing and consistent moisture. Our 245-day growing season gives you plenty of opportunities to find the sweet spot for planting and harvesting.

Starting bok choy indoors in our region is an option, but direct sowing often works just as well, especially with our early spring. If you want a head start, begin indoors from early February through early March, about four weeks before you plan to transplant. Use seed trays filled with a good seed-starting mix, and keep them warm and consistently moist – bottom watering is a great way to avoid damping off.

Transplant your bok choy seedlings outdoors from mid March through late April, once the soil has warmed up a bit. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. Space plants 6-10 inches apart to allow for good air circulation. Be mindful of late-season frosts, which can still occur in some NorCal microclimates during this time.

Direct sowing bok choy is a straightforward method that takes advantage of our mild climate. Sow seeds directly into the garden from early March through mid September. Ensure the soil is well-draining and has warmed up to at least 50°F. Plant seeds about ¼ inch deep and space them 6-10 inches apart. Thin seedlings as needed to maintain proper spacing.

Bok choy thrives with consistent moisture, which is especially important during our dry summers. Aim to keep the soil consistently moist but not waterlogged. A good rule of thumb is to water when the top two inches of soil feel dry to the touch – the "finger test."

During the spring and fall, when temperatures are milder, you'll likely only need to water once or twice a week, providing about 1 inch of water each time. In the heat of summer, you may need to water more frequently, possibly every other day, to prevent bolting. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in some microclimates.

Pay attention to your plants: drooping leaves indicate underwatering, while yellowing leaves can signal overwatering. A layer of mulch, like straw or wood chips, can help retain soil moisture and regulate soil temperature, which is crucial in our variable climate.

You can expect your first bok choy harvest from mid April through late November, about 45 days after planting. Harvest baby bok choy when the leaves are 6-8 inches tall, or wait for the plant to reach full size at 12-15 inches. To harvest, cut the plant just above the base, leaving the roots intact.

This allows the plant to potentially regrow for a second harvest, extending your yield. Regularly harvesting outer leaves also encourages continued production. As the first frost approaches in mid- November, harvest any remaining bok choy, even if it's not fully mature, to prevent damage.

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

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves, especially on young seedlings. You might see small, dark beetles jumping when disturbed.
• What causes it: Small jumping beetles that feed on leaves. They're most damaging to small, young plants.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger. You can also try spraying with neem oil or interplanting with basil or catnip.

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in the leaves. You might also see dark green droppings and white butterflies fluttering around your plants.
• What causes it: These are the larvae of those white cabbage butterflies. They can have multiple generations per season in our warm climate.
• How to fix/prevent it: Bt spray is very effective. Floating row covers can prevent the butterflies from laying eggs. Handpicking the caterpillars is also an option.

Slugs

• What it looks like: Irregular holes in leaves, especially on low-growing plants. You'll often see silvery slime trails on the leaves and soil. Damage is worse at night and in wet weather.
• What causes it: These gastropods feed at night in moist conditions. They hide under mulch and debris during the day.
• How to fix/prevent it: Try beer traps (shallow dishes of beer sunk into the soil). Iron phosphate bait is also effective and pet-safe. Remove any hiding spots and water in the morning so the soil surface dries out by evening.

Bolting in Heat

• What it looks like: The bok choy sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Bok choy is a cool-season crop and will bolt when temperatures rise.
• How to fix/prevent it: Time your plantings for cooler weather (spring and fall). Choose bolt-resistant varieties. Provide shade during warm spells and mulch to keep the soil cool.

Northern California Specific Challenges: Our moderate-to-hot summers and dry conditions can stress bok choy, making it more susceptible to bolting and pest infestations. Consistent watering and providing shade during the hottest part of the day are crucial for success. Also, be mindful of water restrictions and choose water-wise gardening practices.

Good companion plants for bok choy in Northern California include garlic and onions. Their strong scent can deter pests like aphids and cabbage moths, which can be a problem here. Beets are also good companions as they don't compete for the same nutrients. Lettuce and spinach make great ground cover, helping to keep the soil cool and moist, which is beneficial during our dry summers.

Avoid planting bok choy near strawberries or tomatoes. Strawberries can attract slugs, which can then move on to your bok choy. Tomatoes, being heavy feeders, can compete with bok choy for nutrients in the soil.