Bok Choy in Zone 5A — Mountain West

Bok choy is a fantastic addition to the Mountain West garden. Its mild, slightly sweet flavor and crisp texture make it delicious in stir-fries, soups, and salads. Plus, it thrives in our cool nights and intense sunlight, developing a richer flavor than you might find elsewhere.

Our short growing season and alkaline soil can present challenges, but with careful timing and soil amendments, you can enjoy a bountiful harvest of bok choy. With our 138-day growing season, success comes down to timing and choosing varieties that mature quickly.

Starting bok choy indoors isn't always necessary in our climate, but it can give you a jump start, especially for a spring harvest. If you choose to start indoors, sow seeds early to late April, about four weeks before you intend to transplant them.

Use seed trays or small pots filled with a good quality seed-starting mix. Provide warmth (around 70°F) and plenty of light, either from a sunny window or a grow light. Bottom watering is an excellent way to keep the soil consistently moist without overwatering, which is key for good germination. Remember, our springs can be slow to warm up, so indoor starts protect your plants from those lingering cool spells.

Transplant your bok choy seedlings outdoors early May through late June, 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 intense Mountain sun and cooler temperatures.

Space plants 6-10 inches apart in well-drained soil. Be mindful of late spring frosts – keep an eye on the forecast and be ready to cover your transplants if needed. Our cool nights can actually benefit bok choy, but a hard freeze will certainly damage young plants.

Direct sowing is a reliable method for growing bok choy in the Mountain West, especially for succession planting. Sow seeds late April through late July, directly into well-prepared soil. Bok choy prefers soil temperatures between 50°F and 75°F for optimal germination.

Prepare the soil by amending it with compost to improve drainage and fertility. Sow seeds about ¼ inch deep and 6-10 inches apart. Keep the soil consistently moist until seedlings emerge. Direct sowing avoids transplant shock, but be aware that young seedlings are more vulnerable to flea beetles.

Bok choy needs consistent moisture to thrive, especially given our dry climate. Aim to keep the soil evenly moist, but not waterlogged. During the warmer months, you'll likely need to water every other day, or even daily if it's particularly hot and dry. In cooler spring and fall, you can reduce watering to a few times a week.

Use the "finger test" – stick your finger into the soil about two inches deep. If it feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or irrigation. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases, though our low humidity makes this less of a concern than in wetter climates.

Underwatering can cause bolting (premature flowering) and tough leaves. Overwatering, on the other hand, can lead to root rot. Signs of underwatering include wilting leaves and dry soil. Signs of overwatering include yellowing leaves and soggy soil. A layer of mulch, such as straw or wood chips, can help retain moisture and keep the soil cool during the summer months.

You can expect your first harvest of bok choy starting early June through early October, depending on when you planted. Baby bok choy can be harvested when the leaves are 6-8 inches tall, while full-size bok choy is ready when it reaches 12-15 inches.

To harvest, cut the entire head off at the base, just above the soil line. Alternatively, you can harvest individual outer leaves as needed, allowing the plant to continue producing. For continuous production, leave the central bud intact when harvesting.

As the first frost approaches in late September, harvest any remaining bok choy, even if it's not fully mature. Smaller leaves can still be used in salads and stir-fries. You can also try covering your plants with a frost blanket to extend the harvest a bit longer.

Here are some common problems you might encounter growing bok choy in the Mountain West:

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: These small jumping beetles feed on the leaves, and are especially damaging to young plants.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. Delay planting until plants are larger and more resilient. You can also try applying a kaolin clay coating or spraying with neem oil. Interplanting with basil or catnip can help deter them.

Cabbage Worms

• What it looks like: Smooth green caterpillars on the leaves, with irregular holes chewed in the leaves. You might also see dark green droppings and white butterflies hovering around your plants.
• What causes it: These are the larvae of white cabbage butterflies.
• How to fix/prevent it: Bt spray is very effective against cabbage worms. Floating row covers can prevent the butterflies from laying eggs on your plants. You can also handpick the caterpillars or interplant with aromatic herbs like thyme and sage to deter them.

Slugs

• What it looks like: Irregular holes in leaves, especially on low-growing plants. You'll often see silvery slime trails on the leaves and soil. Damage is worse at night and in wet weather.
• What causes it: Slugs are gastropods that 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 dishes of beer sunk into the soil). Iron phosphate bait is a pet-safe option. Remove any hiding spots like mulch or debris. Water in the morning so the soil surface dries out by evening. Copper tape around your beds and diatomaceous earth around your 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. The harvest quality declines rapidly.
• What causes it: Bok choy is a cool-season crop and will bolt when temperatures rise. This happens when days consistently exceed 80°F.
• How to fix/prevent it: Time your plantings for cool weather in the spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells, and use mulch to keep the soil cool. Harvest before the bolting progresses too far.

Mountain West Specific Challenges: Our intense sun can stress bok choy, so providing afternoon shade can be beneficial. Our low humidity can help prevent fungal diseases, but it also means you'll need to be diligent about watering. Dry rainfall can also lead to inconsistent soil moisture, so monitor your plants closely.

Companion planting can help your bok choy thrive. Garlic and onions are great companions because their strong scent deters pests like aphids and cabbage moths. Beets are also beneficial because they improve soil structure and provide nutrients that bok choy needs. Lettuce and spinach make good ground cover, helping to retain moisture and suppress weeds.

Avoid planting bok choy near strawberries or tomatoes. Strawberries can attract slugs, which will also target your bok choy. Tomatoes can stunt the growth of bok choy due to allelopathic chemicals they release into the soil.