Bok Choy in Zone 10A — Southern California

Bok choy is a fantastic addition to your Southern California garden. Its mild, slightly sweet flavor shines in stir-fries, soups, and salads, and its crisp texture adds a delightful crunch. Plus, you can harvest baby bok choy in just a few weeks, giving you quick gardening wins.

While we face challenges like drought and the occasional heat wave, our long growing season means you can enjoy bok choy for much of the year if you time things right. With a little planning, you can easily work around the summer heat and enjoy a year-round harvest from your garden.

Starting bok choy indoors is an option, especially if you want a head start on the growing season or want to avoid flea beetle damage when the plants are very young. Start your seeds mid-December through early January, about four weeks before you plan to transplant them outside. Use seed trays with a good seed-starting mix, and keep them in a warm spot with plenty of light – a sunny windowsill or under grow lights works well.

Remember to water from the bottom by setting the tray in a shallow dish of water; this encourages strong root growth. Because our spring comes early, you will want to have these ready to transplant as soon as the weather permits.

Transplant your bok choy seedlings outdoors mid-January through late February. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Space the plants 6-10 inches apart in well-drained soil. Keep an eye on the weather forecast – even though our winters are mild, we can still get occasional cold snaps or heavy rains that could stress young transplants.

Direct sowing bok choy is an easy and effective method, especially for succession planting throughout the growing season. Sow seeds early January through early November, taking a break during the hottest part of the summer inland. Prepare the soil by loosening it and adding compost.

Bok choy seeds germinate best in soil temperatures between 50°F and 75°F. Plant seeds about ¼ inch deep and space them 6-10 inches apart. Keep the soil consistently moist until the seedlings emerge.

Bok choy needs consistent moisture, especially in our dry Southern California climate. During the cooler months (late fall, winter, and early spring), you'll likely only need to water once or twice a week, depending on rainfall. In the hotter months, especially inland, you might need to water every day or every other day.

Use the "finger test" to check the soil moisture: stick your finger about two inches deep into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week, but adjust based on the weather. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our low-to-moderate humidity.

Yellowing leaves can indicate overwatering, while wilting leaves mean the plant is thirsty. Mulching around your bok choy plants with straw or wood chips will help retain moisture and keep the soil cool, which is especially important during our hot summers and Santa Ana winds.

You can expect your first harvest of bok choy mid-February through early January, about 45 days after planting. You can harvest baby bok choy when the leaves are 6-8 inches tall, or wait for the full-sized plants to reach 12-15 inches. A good sign of ripeness is when the leaves are firm and have a vibrant color.

To harvest, cut the plant above the base, leaving the roots intact. This allows the plant to regrow and produce more leaves for a continuous harvest. As late December approaches, keep an eye on the weather. If a frost is predicted, harvest any remaining bok choy, as frost can damage the leaves.

Flea Beetles

• What it looks like: Tiny round holes in the leaves, creating a "shot-hole" pattern. You might see small, dark beetles jumping around when you disturb the plant.
• What causes it: Flea beetles are attracted to young brassica plants. The dry conditions and warm weather we often experience in early spring and fall can make them more active.
• How to fix/prevent it: Use row covers to protect young seedlings. You can also try spraying with neem oil or kaolin clay. Interplanting with basil or catnip can help deter these pests.

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: Cabbage worms are the larvae of cabbage butterflies. They thrive in our mild climate and can have multiple generations per season.
• How to fix/prevent it: Use Bt (Bacillus thuringiensis) spray, which is very effective against cabbage worms. Floating row covers can prevent the butterflies from laying eggs on your plants. Handpicking the caterpillars is also an option.

Slugs

• What it looks like: Irregular holes in the leaves, especially on low-growing plants. You'll see silvery slime trails on the leaves and soil.
• What causes it: Slugs are gastropods that feed at night in moist conditions. They love to hide under mulch and debris during the day.
• How to fix/prevent it: Set out beer traps (shallow dishes of beer sunk into the soil) to attract and drown the slugs. Iron phosphate bait is another option. Remove hiding spots like mulch and weeds. 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 will bolt (go to seed) when temperatures get too high. This is a common problem during our hot summers inland.
• How to fix/prevent it: Time your plantings to avoid the hottest months. Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest the bok choy before bolting progresses too far.

Southern California Specific Challenges: Our hot, dry summers inland mean you need to be extra vigilant about watering and providing shade to prevent bolting. The low-to-moderate humidity can help reduce fungal diseases, but it also means that pests like flea beetles can thrive. Winter rains can occasionally lead to slug problems, so be prepared to take action.

Garlic and onions are great companions for bok choy because they deter pests like aphids and cabbage moths. Beets help by improving the soil structure and nutrient availability. Lettuce and spinach, as low-growing crops, can help shade the soil and keep it cool, which is especially beneficial during our warmer months.

Avoid planting bok choy near strawberries or tomatoes. Strawberries can attract slugs, which can then move on to your bok choy. Tomatoes can compete for nutrients and space, hindering the growth of your bok choy.