Bok Choy in Zone 6A — Mountain West

Bok choy is a fantastic addition to any Mountain West garden. Its mild, slightly sweet flavor adds a delightful crunch to stir-fries, soups, and salads. Plus, in our climate, the cool nights even in summer enhance its flavor, making it taste even better. It’s also incredibly satisfying to harvest a crop that thrives in our unique conditions.

Our high altitude, intense sun, and short growing season can be a challenge, but with careful timing, you can enjoy a bountiful harvest of bok choy. You have about 153 days between frosts, and bok choy's relatively short maturity time means you can squeeze in a spring and fall crop if you plan well.

Starting bok choy indoors is possible, but honestly, it's often not necessary unless you are trying to get a very early jump on the season. If you choose to start indoors, begin in late March through mid April, about 4 weeks before you intend to transplant.

Use seed trays or small pots filled with a good quality seed-starting mix. Keep the soil consistently moist, and consider bottom watering to prevent damping off. Provide a warm location and plenty of light, either from a grow light or a very sunny window. Remember that spring starts late in the mountains.

Transplant your bok choy seedlings outdoors in early May through mid June, once the danger of hard frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space the plants 6-10 inches apart in well-drained soil. Keep an eye on the weather; even in May and June, we can get unexpected cold snaps or even hail in the mountains. Be prepared to cover your young plants if necessary.

Direct sowing bok choy is a very viable option and often the easiest way to go. Sow seeds mid April through early August for succession planting.

Prepare your soil by loosening it and adding compost. Bok choy prefers a soil temperature of around 60-70°F for germination. Sow seeds about ¼ inch deep and 6-10 inches apart. Thin seedlings as needed once they emerge.

Bok choy thrives with consistent moisture, which is critical in our dry Mountain West climate. You'll need to pay close attention to watering, especially during the hotter parts of the summer.

A good rule of thumb is to water deeply about 1-2 times per week, providing about 1-1.5 inches 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. 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 other regions.

Underwatering will cause the leaves to wilt and can lead to bolting. Overwatering, on the other hand, can cause root rot, though our well-draining alkaline soil helps mitigate this somewhat. Look for yellowing leaves as a sign of overwatering. Mulching around your plants with straw or wood chips will help retain moisture and keep the soil cool.

You can expect your first harvest of bok choy starting in early June and continuing through early October, depending on when you planted. Bok choy matures in about 45 days, so keep an eye on your plants.

Harvest baby bok choy when the leaves are 6-8 inches tall for a more tender flavor. For larger heads, wait until they reach 12-15 inches. To harvest, cut the plant above the base, leaving the roots intact; this allows the plant to regrow and provide you with multiple harvests.

As the first frost approaches in early October, harvest any remaining bok choy, even if it's not fully mature. You can use it in stir-fries or soups, or even pickle it.

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 the leaves, especially on young seedlings. You might see small, dark beetles that jump when disturbed.
• What causes it: These small jumping beetles feed on the leaves. They are most damaging to small, young plants.
• How to fix/prevent it: Row covers are your best bet to protect seedlings during their vulnerable stage. You can also delay planting until the plants are larger and more resilient. Kaolin clay coating and neem oil spray can also help.

Cabbage Worms

• What it looks like: Smooth green caterpillars on the leaves, with irregular holes chewed into them. 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. Floating row covers prevent the butterflies from laying eggs on your plants. You can also handpick the caterpillars.

Slugs

• What it looks like: Irregular holes in the leaves, especially on low-growing plants. You'll see silvery slime trails on the leaves and soil. Damage is worse at night and in wet weather.
• What causes it: Slugs feed at night in moist conditions.
• How to fix/prevent it: Beer traps (shallow dishes of beer sunk into the soil) work well. Iron phosphate bait is pet-safe. Remove any hiding spots like boards or debris. Copper tape around your beds can also deter slugs.

Bolting in Heat

• What it looks like: Your bok choy sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Bok choy is a cool-season crop and bolts when temperatures rise.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties if possible. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest before bolting progresses too far.

Mountain West Specific Challenges: Our intense sun can stress bok choy, making it more susceptible to bolting. The low humidity, while generally beneficial for preventing fungal diseases, means you need to be extra vigilant about watering. Hail can also cause significant damage to the leaves, so consider using netting if hail is in the forecast.

Good companions for bok choy include garlic and onion because their strong scent can deter pests. Beets are helpful because they don't compete for the same nutrients, and lettuce and spinach thrive in similar conditions, making them good neighbors.

Avoid planting bok choy near strawberries or tomatoes. Strawberries can attract slugs that will also munch on your bok choy. Tomatoes can stunt the growth of bok choy.