Bok Choy in Zone 8A — Northern California

Bok choy is a fantastic addition to any Northern California garden. Its mild, slightly sweet flavor and crisp texture make it incredibly versatile in stir-fries, soups, and salads. Plus, here in Zone 8A, our long growing season and mild winters mean you can enjoy fresh bok choy for a good portion of the year.

Even with our Mediterranean climate and dry summers, growing bok choy is manageable with careful planning. Our 255-day growing season provides ample opportunity to plant and harvest this quick-growing vegetable. Just pay attention to watering, and you'll be enjoying homegrown bok choy in no time.

Starting bok choy indoors gives you a head start, especially for a spring crop. Sow seeds indoors from early to late February, about four weeks before you plan to transplant. This is particularly helpful if you want to get a jump on the growing season and avoid potential early heat waves.

Use seed trays with a good seed-starting mix. Keep the soil consistently moist, watering from the bottom to avoid damping off. Place the trays in a warm location with plenty of light. Our early spring warmth can be a bit unpredictable, so starting indoors gives you more control.

Transplant your bok choy seedlings outdoors from early March through late April. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This will help them adjust to the cooler temperatures and stronger sunlight.

Space the seedlings 6-10 inches apart in well-drained soil. Keep an eye on the weather forecast; a late frost can still occur during this period, so be prepared to cover the seedlings if necessary.

Direct sowing bok choy is a great option, especially for succession planting throughout the growing season. Sow seeds directly into the garden from late February through late September. This allows you to harvest fresh bok choy continuously.

Prepare the soil by loosening it and adding compost. Ensure the soil temperature is at least 50°F for optimal germination. Sow seeds 1/4 inch deep and 6-10 inches apart. Keep the soil consistently moist until the seedlings emerge. Direct sowing is convenient, but you'll need to protect young seedlings from pests.

Bok choy needs consistent moisture, especially during our dry summers. Since we get little to no rain during the summer months, supplemental watering is essential for a healthy crop. Aim to keep the soil consistently moist, but not waterlogged.

During the spring and fall, water deeply once or twice a week, providing about 1 inch of water each time. In the heat of summer, you might need to water every other day, or even daily, depending on your specific microclimate and soil type. Use the finger test: if the top 2 inches of soil feel dry, it's time to water. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our low-humidity environment.

Signs of underwatering include wilting leaves and slow growth. Overwatering, on the other hand, can lead to yellowing leaves and root rot. A layer of mulch, like straw or wood chips, can help retain moisture and keep the soil cool, which is especially important during the summer months.

You can expect your first harvest of bok choy from early April through late November, depending on your planting time. Baby bok choy can be harvested when the leaves are 6-8 inches tall, about 45 days after planting. For full-sized bok choy, wait until the heads are 12-15 inches tall.

To harvest, cut the bok choy just above the base, leaving the roots intact. This allows the plant to regrow, providing you with multiple harvests. You can continue to harvest leaves as needed.

As the first frost approaches in mid- November, harvest any remaining bok choy. Even though it's semi-hardy, a hard frost can damage the leaves. You might consider covering plants with frost cloth to extend the harvest a bit longer.

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. You might see small dark beetles that jump when disturbed. Young seedlings are most vulnerable.
• What causes it: These are small jumping beetles that feed on the leaves. They thrive in warm, dry conditions, so spring and early summer can be peak season.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger and more resilient. A kaolin clay coating can deter them. Neem oil spray can help. Interplanting with basil or catnip may also offer some protection.

Cabbage Worms

• What it looks like: Smooth green caterpillars on the leaves, with irregular holes chewed in them. You'll also see dark green droppings and white butterflies hovering around the plants.
• What causes it: These are the larvae of white cabbage butterflies. They love brassicas, and we can have multiple generations per season with our long growing period.
• How to fix/prevent it: Bt spray is very effective. Floating row covers will prevent the butterflies from laying eggs. Handpicking the caterpillars is also an option. Interplant with aromatic herbs like thyme or sage.

Slugs

• What it looks like: Irregular holes in the leaves, especially on low-growing plants. Look for silvery slime trails on the leaves and soil. Damage is often 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: Beer traps (shallow dish of beer sunk into the soil) work well. Iron phosphate bait is pet-safe. Remove any hiding spots. Water in the morning so the soil surface dries out by evening. Copper tape around beds can also deter them.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter. The overall harvest quality declines.
• What causes it: Bok choy is a cool-season crop, and it bolts when temperatures rise. This is especially common during our dry summers.
• How to fix/prevent it: Time your plantings for cooler weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells. Mulch to keep the soil cool. Harvest the bok choy before bolting progresses too far.

Northern California Specific Challenges: The moderate-to-hot heat and dry summers in Northern California can stress bok choy. Consistent watering is crucial to prevent bolting and ensure healthy growth. Pay attention to microclimates in your yard, and provide shade during the hottest part of the day if necessary.

Good companion plants for bok choy include garlic and onions. These alliums help to deter pests like aphids and cabbage worms. Beets are also beneficial, as they don't compete for the same nutrients and can help improve soil structure. Lettuce and spinach make good ground cover, helping to keep the soil cool and moist.

Avoid planting bok choy near strawberries, as they can attract slugs. It's also best to keep bok choy away from tomatoes, as they can both be susceptible to similar fungal diseases. Companion planting can help to maximize your garden space and create a healthier growing environment in Northern California's unique climate.