Bok Choy in Zone 10B — Desert Southwest

Bok choy is a fantastic addition to your Desert Southwest garden. Its mild, slightly sweet flavor and crisp texture make it a versatile ingredient for stir-fries, soups, and salads. The satisfaction of harvesting your own fresh greens, especially in our challenging climate, is hard to beat.

Our extreme heat and arid climate present unique challenges for growing cool-season crops like bok choy. But with careful timing and a few tricks, you can enjoy a bountiful harvest during our two growing seasons. Our 349-day growing season allows for success with careful planning!

Starting bok choy indoors is an option, but often not necessary given our long growing season. If you want a head start, sow seeds indoors from mid-December through early January, about four weeks before you plan to transplant. Use seed trays with a good seed-starting mix, and keep them in a warm location with plenty of light – a sunny windowsill or under grow lights will work.

Bottom watering is key to prevent damping off. Place the tray in a shallow dish of water and let the soil soak it up from the bottom. Given our very-early spring character, indoor starting is a good way to get ahead of the heat.

Transplant your bok choy seedlings outdoors from 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 desert sun and wind.

Space plants 6-10 inches apart in well-drained soil. Keep an eye on the weather; even in late winter, we can get unexpected temperature swings. Be ready to cover your seedlings if a cold snap is predicted.

Direct sowing bok choy is an easy and reliable method in our climate. Sow seeds directly into the garden from early January through early November, taking advantage of our two growing seasons. Prepare the soil by loosening it and adding compost.

Bok choy seeds germinate best when the soil temperature is between 50°F and 70°F. Plant seeds about ¼ inch deep and space them 6-10 inches apart. Thin seedlings as needed to ensure proper spacing.

Consistent watering is essential for bok choy in our arid Desert Southwest climate. Bok choy needs consistently moist soil to thrive, and it will quickly bolt (go to seed) if it dries out, especially when temperatures rise. During the cooler months (January-April and October-December), aim to water deeply about twice a week, providing about 1 inch of water each time.

Use the "finger test" – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. In the hottest part of the year, especially during our monsoon season, you might need to water every other day, or even daily, depending on rainfall. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our humid monsoon conditions.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. Applying a layer of mulch around your bok choy plants helps to retain moisture in the soil and keep the roots cool.

You can expect your first bok choy harvest from mid-February through early January, about 45 days after planting. Harvest baby bok choy when the leaves are 6-8 inches tall, or wait for the full-size heads to reach 12-15 inches. To harvest, cut the entire head above the base, leaving the roots intact.

Bok choy will often regrow after harvesting, giving you a second or even third harvest. Continue to water and fertilize the plants to encourage new growth. As our first frost approaches in late December, harvest any remaining bok choy, even if it's small, to prevent frost damage.

Here are some common problems you might encounter growing bok choy in the Desert Southwest:

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves. You might see small dark beetles that jump when disturbed.
• What causes it: Small jumping beetles that feed on leaves. They are 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 a kaolin clay coating or neem oil spray. Interplant with basil or catnip.

Cabbage Worms

• What it looks like: Smooth green caterpillars on the leaves, with irregular holes chewed in them. Dark green droppings. White butterflies hovering around your plants are a warning sign.
• What causes it: Larvae of white cabbage butterflies. We 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. Handpick caterpillars when you see them. Interplant with aromatic herbs like thyme or sage to deter them.

Slugs

• What it looks like: Irregular holes in leaves, especially low-growing plants. Look for silvery slime trails on leaves and soil. Damage is usually worse at night and in wet weather.
• What causes it: These gastropods feed at night in moist conditions. They hide under mulch, boards, and debris during the day.
• How to fix/prevent it: Use beer traps (shallow dish of beer sunk into the soil). Iron phosphate bait is pet-safe. Remove hiding spots. Water in the morning so the soil surface dries by evening. You can also try copper tape around beds or diatomaceous earth around plants.

Bolting in Heat

• What it looks like: The cool-season crop sends up a flower stalk when temperatures rise. The leaves become tough and bitter.
• What causes it: Extended warm temperatures above the crop's comfort zone. Bok choy bolts when days consistently exceed 80°F.
• How to fix/prevent it: Time plantings for cool weather (spring/fall). Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest before bolting progresses too far.

Desert Southwest Specific Challenges: Our extreme heat can cause bolting, even in bolt-resistant varieties, so shading is essential. The arid humidity means you'll need to monitor soil moisture closely, especially during our dry spells. Even with monsoon moisture, you may still need to water deeply to ensure consistent growth.

Good companions for bok choy in the Desert Southwest include garlic and onions, whose pungent odors deter pests. Beets help improve the soil structure. Lettuce and spinach, being cool-season greens themselves, thrive in similar conditions and don't compete for the same nutrients.

Avoid planting bok choy near strawberries or tomatoes. Strawberries can attract slugs that will also feed on bok choy. Tomatoes can compete for nutrients and sunlight, hindering bok choy growth, especially given our intense sun.