Bok Choy in Zone 4A — Mountain West

Bok Choy is a fantastic addition to any Mountain West garden. Its crisp, mild flavor shines in stir-fries and salads, and it’s quick to mature, delivering fresh greens even with our short growing season. Plus, the cool nights we get even in summer intensify its sweetness.

Our high altitude, intense sun, and sometimes unpredictable weather can present challenges. However, with careful timing and a few tricks, you can easily harvest Bok Choy within our 118-day growing season.

Starting Bok Choy indoors is an option, particularly if you're eager to get a head start. Begin in mid April through early May, about four weeks before you plan to transplant. Use seed trays with a good seed-starting mix and provide warmth and plenty of light – a grow light is ideal.

Don't forget to bottom water your seedlings to encourage strong root development. Starting indoors allows you to get a jump on the season, especially important given our late springs.

Transplant your Bok Choy seedlings outdoors from mid May through early July. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense UV and fluctuating temperatures they'll face.

Space plants 6-10 inches apart. Be mindful of potential late frosts or unexpected hail storms, and consider using row covers for extra protection during those first few weeks.

Direct sowing Bok Choy is a straightforward method that works well in our climate. Sow seeds directly into the garden from early May through mid July. Ensure the soil is well-prepared and has warmed up a bit.

Plant seeds 1/4 to 1/2 inch deep, spacing them 6-10 inches apart. Direct sowing avoids transplant shock, but keep a close eye on soil moisture, as the topsoil can dry out quickly in our dry climate.

Consistent moisture is key to growing healthy Bok Choy in our dry Mountain West climate. While we don't battle humidity, our low rainfall means you'll need to be vigilant about watering. Aim to keep the soil consistently moist, but not waterlogged.

During the warmer months, especially July and August, you might need to water every other day, providing about 1 inch of water per week. Use the "finger test"—stick your finger about 2 inches 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 lead to fungal issues.

Signs of underwatering include wilting leaves and slow growth. Overwatering can cause yellowing leaves and root rot. A layer of mulch, like straw or wood chips, can help retain moisture and regulate soil temperature.

You can expect your first Bok Choy harvest from mid June through late September, depending on when you planted. Baby Bok Choy is ready when it reaches 6-8 inches tall, while full-size heads can be harvested at 12-15 inches.

To harvest, cut the plant just above the base, leaving the roots intact; this encourages regrowth for a second harvest. Regularly harvesting outer leaves also promotes continued production.

As our first frosts approach in mid- September, harvest any remaining Bok Choy, even if it's not fully mature. It's better to harvest early than to lose it to frost.

• 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 beetles are drawn to brassicas. The intense sun can stress young plants, making them more susceptible.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger and more resilient. Kaolin clay coating can deter them. Neem oil spray can also help.

• 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: The larvae of cabbage butterflies. They can be a problem during our warmer months.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent butterflies from laying eggs. Handpick caterpillars whenever you spot them.

• What it looks like: Irregular holes in leaves, especially on lower leaves. Silvery slime trails are a telltale sign.
• What causes it: Slugs thrive in moist conditions. Although our climate is dry, they can find refuge under mulch or in shaded areas.
• How to fix/prevent it: Beer traps work well. Iron phosphate bait is a pet-safe option. Remove any debris where slugs might hide. Water in the morning so the soil surface dries out by evening.

• 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 consistently exceed 80°F. Our intense sun can exacerbate this.
• How to fix/prevent it: Time your plantings for cooler weather in spring or late summer. Choose bolt-resistant varieties. Provide shade during warm spells. Mulch to keep the soil cool. Harvest promptly if bolting starts.

Mountain West Specific Challenges: Our moderate-at-altitude heat, low humidity, and dry rainfall mean you need to be extra vigilant about consistent watering and providing shade during the hottest parts of the day. The intense UV radiation can also stress plants, making them more susceptible to pests.

Garlic and onions are excellent companions for Bok Choy. Their strong scent deters many pests, including flea beetles and cabbage worms. Beets loosen the soil and improve drainage, which is beneficial in our sometimes alkaline soil. Lettuce and spinach are also good companions, as they have similar growing requirements and won't compete for resources.

Avoid planting Bok Choy near strawberries or tomatoes. Strawberries can attract slugs, which will then target your Bok Choy. Tomatoes can stunt the growth of brassicas.