Bok Choy in Zone 8B — Northern California

Bok choy is a fantastic addition to any Northern California garden. Its mild, slightly sweet flavor shines in stir-fries, soups, and salads, and it's incredibly satisfying to harvest your own fresh greens, especially when you can grow them nearly year-round in our Mediterranean climate. Plus, it's a nutritional powerhouse!

We definitely have our share of gardening challenges here – drought, the occasional heatwave, and unpredictable microclimates. But with a little planning and attention to timing, you can easily grow bok choy during our long 269-day growing season.

While you can directly sow bok choy, starting seeds indoors gives you a head start, especially for an early spring harvest. Start your seeds indoors from late January through mid February, roughly four weeks before you intend to transplant them. Use seed trays or small pots filled with a good seed-starting mix.

Keep the soil consistently moist by watering gently from the bottom, setting the tray in a shallow dish of water until the surface looks damp. Place the trays in a warm spot and under grow lights to mimic our increasingly sunny days. Starting indoors gives you more control over the early stages when the weather can still be unpredictable.

Transplant your bok choy seedlings outdoors from early March through mid April, once they have a few sets of true leaves. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. Start with an hour or two of shade, gradually increasing the sun and time each day.

Space the seedlings 6-10 inches apart in well-drained soil amended with compost. Watch out for late frosts, which can still occur. Row covers can provide extra protection if the forecast looks dicey.

Direct sowing bok choy is simple and works well in our climate. Sow seeds from mid February through late September for a continuous harvest. Choose a spot with full sun to partial shade, especially during the warmer months.

Prepare the soil by loosening it and adding compost. Sow seeds about ¼ inch deep and 6-10 inches apart. Keep the soil consistently moist until germination, which usually takes about a week. Direct sowing is great for successive planting, ensuring a steady supply of fresh bok choy.

Bok choy needs consistent moisture, especially during our dry summers. Aim to keep the soil evenly moist, but not waterlogged. A good rule of thumb is to water when the top 2 inches of soil feel dry to the touch – the "finger test."

During the cooler spring and fall months, you might only need to water once or twice a week, providing about an inch of water each time. In the hotter summer months, you may need to water every other day, or even daily, depending on your specific microclimate. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in humid conditions (though low humidity is common here).

Wilting leaves are a sign of underwatering, while yellowing leaves can indicate overwatering. A layer of mulch, like straw or wood chips, can help retain moisture in the soil and keep the roots cool during the heat of summer.

You can start harvesting bok choy as early as early April and continue through early December, depending on when you planted. You can harvest baby bok choy when the leaves are 6-8 inches tall for a more tender flavor. For full-sized bok choy, wait until the heads reach 12-15 inches.

To harvest, cut the entire head off at the base, leaving about an inch of stem. This encourages the plant to send up new leaves for a second harvest. If you see a flower stalk developing as we approach late November, harvest immediately, as the leaves will become bitter once the plant bolts.

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: Flea beetles love brassicas. They thrive in dry conditions, so they can be a real nuisance during our dry summers.
• How to fix/prevent it: Use row covers to protect seedlings. You can also try spraying with neem oil or coating the leaves with kaolin clay. Interplanting with basil or catnip can also help deter them.

Cabbage Worms

• What it looks like: Smooth green caterpillars munching on leaves, leaving irregular holes. You might also see dark green droppings and white cabbage butterflies fluttering around.
• What causes it: Cabbage worms are the larvae of those pretty white cabbage butterflies. They can have multiple generations throughout our long growing season.
• How to fix/prevent it: Bt spray is very effective against cabbage worms. Floating row covers will prevent the butterflies from laying eggs. Handpick any caterpillars you find.

Slugs

• What it looks like: Irregular holes in leaves, especially on low-growing plants. Silvery slime trails are a dead giveaway. Damage is worse at night and in wet weather.
• What causes it: Slugs love moisture and shade. They hide under mulch and debris during the day and come out to feed at night.
• How to fix/prevent it: Beer traps work wonders. You can also use iron phosphate bait, which is safe for pets. Remove any hiding spots around your plants. Water in the morning so the soil surface dries out by evening.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Bok choy is a cool-season crop and bolts when temperatures rise. This is especially a concern during our occasional heatwaves.
• How to fix/prevent it: Time your plantings for spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells. Mulch to keep the soil cool. Harvest promptly if you see signs of bolting.

Northern California Specific Challenges: Our moderate-to-hot summers and dry-summer rainfall pattern mean that you need to be extra vigilant about watering and providing shade for your bok choy. Drought conditions can stress the plants, making them more susceptible to pests and diseases.

Good companions for bok choy include garlic and onions, as their strong scent can help deter pests like flea beetles. Beets help by improving the soil structure and providing nutrients. Lettuce and spinach make great ground covers, helping to retain moisture and suppress weeds.

Avoid planting bok choy near strawberries, as they can attract slugs and snails. Tomatoes are also not ideal companions, as they can compete for nutrients and water.