Romaine Lettuce in Zone 3B — Mountain West

Romaine lettuce, with its crisp texture and slightly bitter edge, brings a refreshing bite to summer salads and sandwiches. The cool nights we get even in the height of summer here in the Mountain West seem to give it an extra boost of flavor, making it a garden staple. Plus, there's real satisfaction in growing your own, knowing it hasn't traveled hundreds of miles to reach your table.

Sure, our high altitude and short growing season (about 108 days) present challenges. But by paying attention to timing and taking a few precautions, you can absolutely enjoy a successful Romaine harvest. Don't worry, you've got this!

Starting Romaine indoors can give you a head start, but honestly, it's often not necessary given how well it direct sows. If you're itching to get going early, or want to squeeze in a late fall crop, starting seeds indoors from early to late April is the way to go. This gives you about four weeks to get them going before transplanting.

Use seed trays with a good seed-starting mix. Keep them warm (around 70°F) and provide plenty of light – a grow light works best. To avoid damping off, water from the bottom by setting the tray in a shallow dish of water until the soil surface is moist. Remember, our spring can be late, so don't be tempted to rush things!

Transplanting Romaine seedlings outdoors happens from mid May through early June, once the risk of hard frost has passed. Before planting, you'll want to harden them off. This means gradually exposing them to outdoor conditions for about a week. Start with an hour or two of shade, increasing the time each day.

Space your Romaine plants 8-10 inches apart in well-drained soil. Even in May, we can still get some chilly nights, so keep an eye on the forecast and be ready to cover them if needed.

Direct sowing Romaine is a great option for us Mountain gardeners, especially since our summers are moderate. You can sow seeds directly into the garden from late April through late June. This gives you a succession of harvests throughout the growing season.

Prepare your soil by loosening it and removing any rocks or debris. 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. The downside to direct sowing is that the seedlings are more vulnerable to pests and weather fluctuations.

Consistent watering is key to growing crisp, delicious Romaine in our dry Mountain climate. While we don't have the humidity to worry about like other regions, our low rainfall means you'll need to be diligent. Romaine needs consistent moisture to stay tender, otherwise it will bolt faster than leaf lettuce in summer heat.

During the spring, when temperatures are cooler, water deeply once or twice a week, providing about 1 inch of water. As the weather warms up in summer, increase watering to every other day, providing 1-2 inches of water per week. 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 lead to disease problems. Signs of underwatering include wilting and yellowing leaves. Overwatering can cause root rot, so make sure your soil drains well. A light layer of mulch, like straw or shredded bark, can help retain moisture and keep the soil cool.

You can expect your first Romaine harvest from early July through mid September, depending on when you planted. Romaine is ready to harvest when the outer leaves are 6-8 inches long, or when the whole head feels firm and full-sized. Don't wait too long, though; once the center stem starts to elongate, the leaves will become bitter.

To harvest, you can either cut off the outer leaves as needed or harvest the entire head. If you're harvesting outer leaves, be careful not to damage the rest of the plant. For a continuous harvest, leave the inner leaves to continue growing.

As our first frost approaches in early September, harvest any remaining heads to enjoy in salads or sandwiches. You can also try covering your plants with a frost blanket to extend the harvest a bit longer.

Here are some common problems you might encounter with Romaine lettuce in the Mountain West:

Bolting in Heat

• What it looks like: A tall flower stalk shoots up from the center of the lettuce head. The leaves become tough and bitter.
• What causes it: Extended warm temperatures. Romaine is a cool-season crop and bolts when days consistently exceed 80°F.
• How to fix/prevent it: Time your plantings for cooler weather in spring and fall. Choose bolt-resistant varieties. Provide shade with row covers during warm spells. Mulch to keep the soil cool. Harvest immediately if you see signs of bolting.

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. Populations explode in warm weather.
• How to fix/prevent it: Strong water spray to knock them off. Encourage ladybugs and lacewings. Insecticidal soap for heavy infestations. Neem oil works systemically.

Slugs

• What it looks like: Irregular holes in leaves, especially on lower leaves. Silvery slime trails.
• What causes it: These critters 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 like rocks and boards. 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.
• 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 you need to be extra vigilant about watering and providing shade. The intense UV at our altitude can also stress plants, making them more susceptible to bolting and other problems.

Companion planting can help your Romaine thrive. Carrots are good companions because their scent deters lettuce root aphids, and they don't compete for the same nutrients. Radishes are quick to mature and can help break up the soil, making it easier for lettuce roots to grow. Strawberries make a good ground cover that helps retain moisture and suppress weeds. Chives and onions deter aphids and other pests with their strong scent.

Avoid planting Romaine near celery and parsley. Celery attracts whiteflies, which can also infest lettuce. Parsley can stunt the growth of lettuce. By choosing the right companions, you can create a healthier and more productive garden.