Bok Choy in Zone 8B — Pacific Northwest

Bok choy is a fantastic addition to any Pacific Northwest garden. Its mild, slightly sweet flavor makes it incredibly versatile in stir-fries, soups, and salads. Plus, it thrives in our cool, mild summers and even benefits from the cool nights, developing a sweeter taste. There's nothing quite like harvesting your own fresh bok choy, especially when our long, mild fall gives you ample time to enjoy it.

While the PNW offers a welcoming climate for bok choy, we do face challenges like slugs and the potential for bolting during unexpected warm spells. However, with careful timing and attention, you can easily overcome these hurdles and enjoy a bountiful harvest during our 210-day growing season.

Starting bok choy indoors in the Pacific Northwest isn't always necessary, but it can give you a head start, especially if our spring weather is slow to warm. You can start seeds indoors from early to late March, 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. Bottom watering helps prevent damping off, so set the tray in a shallow dish of water and let the soil absorb it from below. Given our often overcast spring days, grow lights might be your best bet for strong, healthy seedlings.

Transplant your bok choy seedlings outdoors from early April through mid May, after they've developed a few true leaves. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the cooler temperatures and stronger sunlight.

When transplanting, space the seedlings 6-10 inches apart to allow for adequate growth. Keep an eye on the weather forecast, as late frosts can still occur during this time. If frost is predicted, cover the seedlings with horticultural fleece or cloches.

Direct sowing bok choy is a simple and effective method for Pacific Northwest gardeners. You can sow seeds directly into the garden from late March through early September, ensuring a continuous harvest.

Prepare the soil by loosening it and adding compost or other organic matter. Bok choy prefers soil temperatures between 50°F and 70°F for optimal germination. Sow seeds about ¼ inch deep and 6-10 inches apart. Thin seedlings as needed once they emerge. Direct sowing is especially useful in the late summer for a fall crop.

Bok choy needs consistent moisture to thrive in the Pacific Northwest. While our mild summers and dry-summer rainfall mean we don't often face extreme heat, keeping the soil consistently moist is crucial to prevent bolting and ensure healthy growth. Aim for about 1 inch of water per week, adjusting based on rainfall.

The "finger test" is your best friend: stick your finger about 2 inches deep into the soil. If it feels 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 sometimes humid conditions, even though it's generally a dry-summer climate.

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 around the plants helps retain moisture and suppress weeds, which is especially useful during our dry summer months.

You can expect your first bok choy harvest from early May through early November in the Pacific Northwest, depending on when you planted. Baby bok choy can be harvested when it reaches 6-8 inches tall, while full-size bok choy is ready at 12-15 inches.

To harvest, cut the plant above the base, leaving the roots intact. This allows the plant to regrow, providing you with multiple harvests. Regularly harvesting outer leaves also encourages continued production.

As our first frost approaches in early November, harvest any remaining bok choy, even if it's not fully mature. You can use the smaller leaves in salads or stir-fries. If frost is light, you can extend harvest by covering plants.

Here are some common problems you might encounter growing bok choy in the Pacific Northwest:

Flea Beetles

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

Cabbage Worms

• What it looks like: Smooth green caterpillars on brassica leaves. Irregular holes chewed in leaves, and dark green droppings on the plants. You might also see white butterflies fluttering around.
• What causes it: These are the larvae of white cabbage butterflies. They can have multiple generations in a season, especially if we have a warmer than usual summer.
• How to fix/prevent it: Bt spray is very effective. Floating row covers will prevent the butterflies from laying eggs on your plants. Handpick caterpillars whenever you see them. Interplant with aromatic herbs like thyme and sage to deter the butterflies.

Slugs

• What it looks like: Irregular holes in leaves, especially on low-growing plants. Silvery slime trails on leaves and soil. Damage is worse at night and in wet weather.
• What causes it: Slugs thrive in our moist Pacific Northwest climate, especially during our wet springs and falls. They feed at night and 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. Use iron phosphate bait, which is pet-safe. Remove hiding spots like boards and debris. Water in the morning so the soil surface dries by evening. Copper tape around beds and diatomaceous earth around plants can also help.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Bolting is triggered by extended warm temperatures. Bok choy is a cool-season crop and bolts when temperatures consistently exceed 80°F.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest bok choy before bolting progresses.

Pacific Northwest Specific Challenges: Our mild heat and dry-summer rainfall can create ideal conditions for slugs and bolting. Monitor your plants closely, especially during warmer periods, and take steps to manage moisture levels and protect against pests. Late blight is not usually a problem for bok choy.

Good companions for bok choy in the Pacific Northwest include garlic and onions, whose strong scent deters pests like aphids and cabbage moths. Beets help to loosen the soil, improving drainage, which is crucial in our wet springs. Lettuce and spinach make great ground cover, suppressing weeds and keeping the soil cool and moist during our dry summer months.

Avoid planting bok choy near strawberries, as they can attract slugs, which are already a common problem in our region. Tomatoes can compete for nutrients and attract similar pests, so it's best to keep them separate.