Romaine Lettuce in Zone 7B — Pacific Northwest

Romaine lettuce is a fantastic addition to any Pacific Northwest garden. Its crisp texture and slightly sweet flavor make it perfect for salads, wraps, or even a quick sauté. Plus, with our cool nights and mild summers, Romaine thrives here, developing a superior flavor compared to what you'll find in the grocery store.

While we enjoy a long growing season of around 193 days, our wet springs and the potential for a short burst of heat in the summer can present challenges. Don't worry, with a little planning and attention to timing, you can enjoy a steady supply of homegrown Romaine from late spring well into the fall.

Starting Romaine indoors is an option if you want a head start, but it's not strictly necessary in our climate. If you choose to start indoors, begin in late February through mid March, about four weeks before you plan to transplant. Use seed trays with a good seed-starting mix, and provide consistent warmth (around 70°F) and bright light, either from a sunny window or a grow light.

Keep the soil consistently moist, and consider bottom watering to prevent damping off. Our overcast spring days can sometimes slow growth, so supplemental light will give your seedlings the best start.

Transplant your Romaine seedlings outdoors in early to late April, once the soil has warmed up a bit. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This will help them adjust to the cooler temperatures and stronger sunlight.

Space your Romaine plants 8-10 inches apart to allow for good air circulation and prevent overcrowding, which can lead to problems like tip burn. Keep an eye on the weather forecast; a late frost can still happen in April, so be prepared to cover your seedlings if necessary.

Direct sowing Romaine is a simple and effective method, especially for later crops. Sow seeds mid March through early August for a continuous harvest. Choose a spot with well-drained soil and full sun to partial shade, especially for summer plantings.

Prepare the soil by loosening it and adding compost. Sow seeds about ¼ inch deep and 8-10 inches apart, or thin seedlings to that spacing after they emerge. Keep the soil consistently moist until germination, which usually takes about a week. Direct sowing works great in our mild summers.

Consistent watering is key to growing crisp, delicious Romaine in the Pacific Northwest. While our summers are relatively mild, they can be dry, and Romaine needs consistent moisture to thrive. Aim to keep the soil evenly moist, but not waterlogged.

During our wet springs, you may not need to water at all, relying on natural rainfall. As the dry summer months approach, check the soil moisture regularly. Use the "finger test" – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. Generally, aim for about 1 inch of water per week, either from rain or irrigation. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our sometimes humid conditions.

Signs of underwatering include wilting and dry leaf edges. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, such as straw or shredded leaves, can help retain moisture and keep the soil cool, which is especially helpful during warmer spells.

You can expect your first Romaine harvest from late May through early November, depending on when you planted. Romaine is ready to harvest about 65 days after planting. You can harvest outer leaves when they are 6-8 inches long for a continuous harvest, or cut the entire head when it's firm and full-sized.

To harvest individual leaves, simply snap or cut them off near the base of the plant. For a whole head harvest, cut the stem at the base of the plant with a sharp knife. Harvest before the center stem starts to elongate, as this indicates bolting, which will make the leaves bitter.

As the first frost approaches in late October, harvest any remaining mature heads. You can also cover plants with a frost blanket to extend the harvest a bit longer, taking advantage of our long, mild fall weather.

Here are some common problems you might encounter growing Romaine in the Pacific Northwest:

Bolting in Heat

• What it looks like: A tall flower stalk emerges from the center of the lettuce head. The leaves become bitter and tough.
• What causes it: Extended warm temperatures, especially days consistently above 80°F, trigger bolting. This is more likely to happen during a heatwave in the summer.
• How to fix/prevent it: Choose bolt-resistant varieties. Plant in early spring or late summer for cooler growing conditions. Provide shade during warm spells with shade cloth. Water deeply and mulch to keep the soil cool. Harvest lettuce as soon as it's ready to prevent bolting.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and undersides of leaves. Sticky honeydew residue and curled, distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects that thrive in warm weather.
• How to fix/prevent it: Spray plants with a strong stream of water to dislodge aphids. Encourage beneficial insects like ladybugs and lacewings. Use insecticidal soap or neem oil for heavy infestations.

Slugs

• What it looks like: Irregular holes in leaves, especially on lower leaves. Silvery slime trails on leaves and soil.
• What causes it: Slugs thrive in our moist, mild climate, especially during wet springs.
• How to fix/prevent it: Use beer traps or iron phosphate bait. Remove hiding spots like weeds and debris. Water in the morning to allow the soil surface to dry out by evening. Apply copper tape around beds or diatomaceous earth around plants.

Tip Burn

• What it looks like: Brown, dried edges on inner lettuce leaves, sometimes spreading to outer leaves.
• What causes it: Calcium deficiency due to inconsistent watering, especially during warm weather.
• How to fix/prevent it: Water consistently to maintain even soil moisture. Avoid fertilizers high in ammonium nitrogen. Ensure good soil calcium levels by adding lime to the soil if needed. Choose tip burn-resistant varieties.

Pacific Northwest Specific Challenges: Our mild summers generally benefit Romaine, but a sudden heatwave can still cause bolting. The dry-summer rainfall pattern means consistent watering is crucial during those months. Slug pressure is a constant concern, especially during our wet springs, so be vigilant with your slug control methods. Late blight is more of a tomato issue, but keep it in mind if you grow both together.

Companion planting can help your Romaine lettuce thrive. Carrots are great companions because they deter lettuce root aphids. Radishes are quick-growing and help break up the soil, improving drainage. Strawberries make a good ground cover and help retain moisture. Chives and onions deter aphids and other pests with their strong scent.

Avoid planting Romaine near celery and parsley. Celery competes for nutrients and can attract pests that also affect lettuce. Parsley can stunt the growth of lettuce.