Romaine Lettuce in Zone 6B — Mountain West

Romaine lettuce is a fantastic addition to any Mountain West garden. Its crisp texture and mild flavor make it incredibly versatile in salads, wraps, and even grilled dishes. Plus, the satisfaction of harvesting your own fresh lettuce, especially with our intense sunlight giving it extra flavor, is hard to beat.

Our high-altitude climate presents some unique challenges, like intense UV and a short growing season, but with careful timing and a few smart strategies, you can enjoy a steady supply of delicious Romaine from early summer well into fall. Our 163-day growing season is plenty of time to get multiple harvests if you plan right.

Starting Romaine lettuce indoors is an option, but not always necessary given our ability to direct sow. If you want a head start, particularly for an earlier spring harvest, starting seeds indoors from early to late March is your best bet. This gives you about 4 weeks to get them going before transplanting.

Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist, and bottom watering is a great way to prevent damping off. Place the trays in a warm location with plenty of light – a sunny windowsill or under grow lights works well. Remember, spring can be late coming in the Mountains, so indoor starts give you more control.

Transplant your Romaine lettuce seedlings outdoors from mid April through early May, after the danger of hard frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense sun and cooler nights we often experience.

Space your seedlings 8-10 inches apart in well-drained soil. Be prepared for unexpected late-season cold snaps, which can happen even in late April. Row covers can be a lifesaver if temperatures dip unexpectedly.

Direct sowing Romaine lettuce is a simple and effective method, especially for succession planting. You can sow seeds directly into the garden from late March through mid July, giving you a long window for multiple harvests. The advantage here is simplicity, but you're more at the mercy of the weather.

Prepare the soil by loosening it and adding compost to improve drainage and fertility. Sow seeds about ¼ inch deep and keep the soil consistently moist until they germinate. Thin seedlings to 8-10 inches apart once they have a few true leaves.

Consistent moisture is key to growing crisp, tender Romaine lettuce in our dry Mountain West climate. Unlike some regions, we don't have humidity on our side, so regular watering is essential, especially during the warmer months. The goal is to prevent the lettuce from bolting prematurely, as it's more prone to doing so in heat compared to leaf lettuce.

In the spring and fall, when temperatures are cooler, aim to water deeply about 1-2 times per week, providing around 1 inch of water each time. During the hotter summer months, you might need to water every other day, especially if you notice the leaves wilting. 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 diseases in more humid climates, though we don't typically have that problem here. Just be aware that overhead watering can cause tip burn (described below), so aim for the base of the plant. Mulching around your lettuce plants with straw or wood chips helps retain moisture in our dry air and keeps the soil cool. Signs of underwatering include wilting and stunted growth, while overwatering can lead to root rot.

You can expect your first Romaine lettuce harvest from early June through mid October, depending on when you planted. Romaine is ready to harvest about 65 days after planting. Look for outer leaves that are 6-8 inches long, or harvest the entire head when it feels firm and full-sized.

To harvest individual leaves, simply cut them from the base of the plant, leaving the inner leaves to continue growing. For a whole head harvest, cut the stem at the base of the plant. Harvest before the center stem elongates, as this indicates the plant is bolting and the leaves will become bitter.

To extend your harvest, especially as we approach our first frost in early October, consider using row covers to protect the plants from cold temperatures. You can also harvest smaller, younger leaves for salads if a frost is imminent.

Here are four common problems you might encounter growing Romaine lettuce in the Mountain West:

Bolting in Heat

• What it looks like: A tall flower stalk emerging from the center of the lettuce head. Leaves become tough and bitter.
• What causes it: Extended warm temperatures, especially when days consistently exceed 80°F. The plant is trying to reproduce due to stress.
• How to fix/prevent it: Time your plantings for cooler weather (spring and fall). Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest lettuce promptly once it reaches maturity.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects that thrive in warm weather.
• How to fix/prevent it: Strong water spray to knock them off. Encourage beneficial insects like ladybugs and lacewings. Use insecticidal soap for heavy infestations. Avoid excess nitrogen fertilizer.

Slugs

• What it looks like: Irregular holes in leaves, especially on low-growing plants. Silvery slime trails on leaves and soil.
• What causes it: Gastropods that feed at night in moist conditions.
• How to fix/prevent it: Beer traps (shallow dish of beer sunk into soil). Iron phosphate bait (pet-safe). Remove hiding spots. Water in the morning so the soil surface dries by evening. Diatomaceous earth around plants.

Tip Burn

• What it looks like: Brown, dried edges on inner lettuce leaves. Can affect outer leaves in severe cases.
• What causes it: Calcium uptake problem caused by inconsistent watering, similar to blossom end rot in tomatoes. Worsened by high temperatures.
• How to fix/prevent it: Water consistently. Avoid fertilizer high in ammonium nitrogen. Ensure good soil calcium levels. Choose resistant varieties. Provide shade in warm weather.

Mountain West Specific Challenges: Our moderate-at-altitude heat, combined with low humidity and dry rainfall, means consistent watering is crucial to prevent bolting and tip burn. The intense UV can also stress plants, so providing some afternoon shade can be beneficial, especially during the hottest part of the summer.

Companion planting can help your Romaine lettuce thrive. Carrots are good companions because their scent deters lettuce root aphids. Radishes break up the soil and deter flea beetles. Strawberries provide ground cover, which helps retain moisture. Chives and onions repel aphids and other pests with their strong scent.

Avoid planting Romaine lettuce near celery and parsley, as they can attract the same pests, increasing the risk of infestation.