Bok Choy in Zone 4B — Mountain West

Bok choy is a fantastic addition to any Mountain West garden. Its mild, slightly sweet flavor and crisp texture make it incredibly versatile in stir-fries, soups, and salads. Plus, it thrives in our cool nights and intense sunlight, developing a wonderful flavor that rivals anything you'll find in the store.

Our short growing season and alkaline soil can present challenges, but with careful timing, you can easily enjoy a bountiful harvest of bok choy. Considering our 128-day growing season, it's all about getting the timing right to avoid the worst of the summer heat and those early fall frosts.

Starting bok choy indoors is possible, but it's honestly not always necessary given our short season. If you want a super early start, sow seeds indoors from early April through early May, about four weeks before you plan to transplant. Use seed trays with a good seed-starting mix and keep them consistently moist with bottom watering to avoid damping off.

Provide warmth and plenty of light, especially since our spring weather can be unpredictable. A simple grow light will ensure your seedlings don't get leggy waiting for transplant time, because our spring weather is often later than you wish it was.

Transplant your bok choy seedlings outdoors from mid-May through late June, after the risk of hard frost has passed. Be sure to harden them off for about a week before transplanting, gradually exposing them to outdoor conditions. This is critical to help them withstand our intense UV and temperature swings.

Space the plants 6-10 inches apart in well-draining soil. Keep an eye on the forecast for late frosts, which can still happen even in June at our altitude. A row cover can provide extra protection if needed.

Direct sowing bok choy is a great option in our Mountain West climate, especially for succession planting. Sow seeds from early May through late July, ensuring the soil temperature is at least 50°F. Prepare the soil by amending with compost to improve drainage and nutrient content.

Plant seeds about ¼ inch deep and space them 6-10 inches apart. Keep the soil consistently moist, especially during germination. Direct sowing is a good way to get a continuous harvest throughout the growing season.

Watering bok choy correctly is crucial in our dry Mountain West climate. The key is to keep the soil consistently moist, but not waterlogged. Bok choy is not drought-tolerant and will bolt quickly if it dries out, especially during warm spells.

During the spring and fall, when temperatures are cooler, water deeply about once a week, providing about 1 inch of water. In the hotter summer months, you may need to water every other day, or even daily, especially with our intense sun. Use the "finger test" – if the top 2 inches of soil feel dry, it's time to water.

Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases, even with our low humidity. Signs of underwatering include wilting leaves, while overwatering can lead to yellowing leaves and root rot. A layer of mulch, like straw or wood chips, will help retain moisture and keep the soil cool.

You can expect your first bok choy harvest from mid-June through late September, about 45 days after planting. You can harvest baby bok choy when it's 6-8 inches tall, or wait for the full size of 12-15 inches.

To harvest, cut the plant above the base, leaving the roots intact. This allows the plant to regrow, giving you a continuous harvest. As the first frost approaches around mid-September, harvest any remaining bok choy, even if it's not fully mature, as it won't survive a hard freeze.

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

Flea Beetles

• What it looks like: Tiny round holes in the leaves, creating a "shot-hole" pattern. You'll see small, dark beetles that jump when disturbed.
• What causes it: These small jumping beetles feed on the leaves, and they're most damaging to young seedlings.
• 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. Interplanting with basil or catnip can also help deter them.

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 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. Use floating row covers to prevent the butterflies from laying eggs. Handpick the caterpillars when you see them. Interplant with aromatic herbs like thyme and sage to deter the butterflies.

Slugs

• What it looks like: Irregular holes in the leaves, especially on low-growing plants. You'll also see silvery slime trails on the leaves and soil.
• What causes it: Slugs feed at night in moist conditions, hiding under mulch 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 also effective and pet-safe. Remove any hiding spots like mulch or boards. Water in the morning so the soil surface dries out 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: Bok choy is a cool-season crop and will bolt when temperatures rise.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells and mulch to keep the soil cool. Harvest before bolting progresses too far.

Mountain West Specific Challenges: Our high altitude and intense sun can exacerbate bolting, so providing shade during the hottest part of the day is crucial. The low humidity can help reduce fungal diseases, but it also means you need to be extra vigilant about watering. The dry rainfall can cause the alkaline soil to dry out quickly, so be sure to mulch well and amend the soil with plenty of organic matter.

Companion planting can be very helpful for bok choy in our Mountain West gardens. Garlic and onions are great companions because they deter pests like aphids and cabbage worms. Beets help to loosen the soil, improving drainage, which is important in our often-compacted alkaline soils.

Lettuce and spinach are also good companions as they provide ground cover, helping to retain moisture and suppress weeds. Avoid planting bok choy near strawberries or tomatoes. Strawberries compete for nutrients and water, while tomatoes can attract pests that also affect bok choy.