Romaine Lettuce in Zone 7A — Mountain West

Romaine lettuce is a fantastic addition to any Mountain West garden. Its crisp texture and slightly bitter flavor add a refreshing element to salads, sandwiches, and even grilled dishes. Plus, there's nothing quite like the satisfaction of harvesting your own fresh greens, especially when those cool nights at our altitude help to sweeten them up.

Growing Romaine in our region does present some unique challenges: intense sun, alkaline soil, and a short growing season. But with careful timing and a few tricks, you can enjoy a steady supply of delicious lettuce from late spring to mid-fall. You have about 173 days to work with, so let's make the most of them.

Starting Romaine lettuce indoors gives you a head start, but it's not strictly necessary in our zone. If you want to get a jump on the season, aim to start seeds indoors from early to late March, about four weeks before you plan to transplant.

Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist (bottom watering works great to prevent damping off) and provide plenty of light, either with a grow light or a sunny windowsill. Remember, our spring weather can be unpredictable, so starting indoors provides some insurance against late frosts.

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

When transplanting, space the seedlings about 8-10 inches apart in well-drained soil. Be prepared to protect them from unexpected late frosts with row covers or blankets. Those cool nights, even in spring, can sometimes dip below freezing.

Direct sowing Romaine lettuce is a perfectly viable option in the Mountain West. Sow seeds from late March through late July for a continuous harvest. Prepare the soil by loosening it and adding compost. Romaine seeds germinate best in soil temperatures between 60-70°F, so wait until the soil has warmed up a bit.

Sow seeds about ¼ inch deep and space them 8-10 inches apart. Keep the soil consistently moist until the seedlings emerge. Thin the seedlings to the strongest plant once they are a few inches tall.

Consistent watering is crucial for growing crisp, tender Romaine lettuce in our dry Mountain climate. Unlike some regions, we don't have the humidity to rely on, so we need to be diligent. Aim for about 1-1.5 inches of water per week, especially during the heat of summer.

Check the soil moisture regularly using the "finger test": stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Water deeply at the base of the plants to encourage strong root growth and reduce the risk of fungal diseases in our low-humidity environment. Overhead watering can work, but water early in the day so the foliage dries quickly.

Underwatering will result in bitter, tough leaves, while overwatering can lead to root rot. Signs of underwatering include wilting leaves and dry soil. Overwatering can manifest as yellowing leaves and soggy soil. A layer of mulch around your lettuce plants will help retain moisture and keep the soil cool, which is especially important during our hot summer days.

You can expect your first Romaine lettuce harvest from late May through mid October, depending on when you planted. Look for outer leaves that are 6-8 inches long, or harvest the whole head when it feels firm and full-sized. The key is to harvest before the center stem starts to elongate, as this indicates that the plant is bolting.

To harvest individual leaves, simply cut them off near the base of the plant. This will allow the plant to continue producing new leaves for several weeks. For a whole head harvest, cut the stem at the base of the plant. As the first frost approaches in early October, harvest any remaining heads to enjoy before the cold weather sets in.

Here are some common problems you might encounter when 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. The leaves become tough and bitter.
• What causes it: Extended periods of warm weather, especially when daytime temperatures consistently exceed 80°F.
• How to fix/prevent it: Time your plantings for cool weather, choose bolt-resistant varieties, provide shade during warm spells, mulch to keep the soil cool, and harvest before bolting progresses.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects that thrive in warm weather.
• How to fix/prevent it: Knock them off with a strong water spray, encourage natural predators like ladybugs and lacewings, use insecticidal soap for heavy infestations, and 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: Use beer traps, iron phosphate bait (pet-safe), remove hiding spots, water in the morning so the soil surface dries by evening, and apply diatomaceous earth around plants.

Tip Burn

• What it looks like: Brown, dried edges on inner lettuce leaves.
• What causes it: Calcium uptake problems caused by inconsistent watering, worsened by high temperatures.
• How to fix/prevent it: Water consistently, avoid fertilizers high in ammonium nitrogen, ensure good soil calcium levels, choose resistant varieties, and provide shade in warm weather.

Mountain West Specific Challenges: Our moderate-at-altitude heat, combined with low humidity and dry rainfall, means that consistent watering and protection from intense sun are crucial for preventing bolting and tip burn. The intense UV light can also stress plants, so providing some afternoon shade can be beneficial.

Companion planting can help your Romaine lettuce thrive in the Mountain West.

• Carrots: Carrots loosen the soil, making it easier for lettuce roots to grow.
• Radishes: Radishes deter pests that might attack lettuce and act as a quick-growing marker crop.
• Strawberries: Strawberries provide ground cover, helping to retain moisture and suppress weeds.
• Chives and Onions: These alliums repel aphids and other pests.

Avoid planting Romaine lettuce near:

• Celery: Celery competes for nutrients and water, hindering lettuce growth.
• Parsley: Parsley attracts aphids, which can then spread to your lettuce.