Romaine Lettuce in Zone 5B — Midwest

Romaine lettuce is a fantastic addition to any Midwest garden. Its crisp texture and mild flavor make it perfect for salads, wraps, and even grilling. Plus, it thrives in our fertile soil and enjoys the adequate rainfall we typically get during the growing season.

While we do have to contend with variable springs and occasional summer heat spells, Romaine lettuce is relatively easy to grow if you time your plantings right. With our 168-day growing season, you can enjoy multiple harvests of this versatile green.

Starting Romaine lettuce indoors in the Midwest gives you a head start, especially if you're eager to get a spring crop going. Start your seeds indoors from early to late March, about 4 weeks before you plan to transplant them outside. Use seed trays filled with a good seed-starting mix, and keep them in a warm spot with plenty of light – a sunny windowsill or under grow lights works well.

Make sure to keep the soil consistently moist, and consider bottom watering to prevent damping off. Starting indoors can be beneficial, but direct sowing works well too, so don't feel obligated if you're short on space or time.

Transplant your Romaine lettuce seedlings outdoors from mid April through early May, once the risk 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 sun and wind.

When transplanting, space the seedlings about 8-10 inches apart. Keep an eye on the weather forecast – a late frost can still happen, so be prepared to cover your seedlings if necessary.

Direct sowing Romaine lettuce is a simple and effective method, especially for succession planting throughout the season. Sow seeds directly into the garden from late March through late July. Make sure the soil is well-prepared and the temperature is consistently above 40°F.

Plant seeds about ¼ inch deep and space them 8-10 inches apart. Thin the seedlings as they grow, selecting the strongest plants. Direct sowing is great because it avoids transplant shock, but you'll need to stay on top of weeding.

Watering is crucial for Romaine lettuce, especially in the Midwest climate. Aim for consistent moisture to ensure crisp, tender leaves, as Romaine tends to bolt faster than leaf lettuce when stressed by heat. During the spring and fall, when temperatures are cooler, water about 1 inch per week, depending on rainfall.

In the summer, when we can experience moderate-to-hot heat and moderate-to-humid conditions, increase watering to 1-2 inches per week. Use the "finger test" – stick your finger about 2 inches deep 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 in our humid climate.

Signs of underwatering include wilting and slow growth, while overwatering can lead to yellowing leaves and root rot. A layer of mulch, like straw or shredded leaves, can help retain moisture and keep the soil cool during those summer heat spells.

You can expect your first harvest of Romaine lettuce from early June through mid October, about 65 days after planting. Look for outer leaves that are 6-8 inches long, or harvest the whole head when it feels firm and full-sized. It's best to harvest before the center stem starts to elongate, as this indicates bolting.

To harvest, either cut the outer leaves as needed, allowing the plant to continue producing, or cut the entire head at the base. For continued production, keep the plant watered and fertilized lightly. 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 growing Romaine lettuce in the Midwest:

Bolting in Heat

• What it looks like: A tall flower stalk emerges from the center of the lettuce head. The leaves become tough and bitter.
• What causes it: Romaine lettuce is a cool-season crop, and it bolts when temperatures consistently exceed 80°F. Our summer heat spells can trigger this.
• How to fix/prevent it: Time your plantings for cooler weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest lettuce before bolting progresses too far.

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. Avoid excess nitrogen fertilizer.

Slugs

• What it looks like: Irregular holes in leaves, especially on lower leaves. Silvery slime trails on leaves and soil.
• What causes it: Slugs feed at night in moist conditions. They hide under mulch and debris during the day.
• How to fix/prevent it: Beer traps. Iron phosphate bait (pet-safe). Remove hiding spots. Water in the morning. Copper tape around beds. 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 and 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.

Midwest Specific Challenges: Our moderate-to-hot summer heat and moderate-to-humid conditions can create a perfect storm for bolting, aphids, and fungal diseases. Consistent watering and proper air circulation are key to mitigating these issues.

Companion planting can be a great way to improve the health and yield of your Romaine lettuce. Carrots are good companions because they deter lettuce root aphids. Radishes help to break up the soil and can act as a trap crop for flea beetles. Strawberries provide ground cover and help retain moisture.

Chives and onions deter aphids and other pests with their strong scent. Avoid planting Romaine lettuce near celery and parsley, as they can attract similar pests and compete for nutrients.