Romaine Lettuce in Zone 6B — Pacific Northwest

Romaine lettuce is a fantastic addition to any Pacific Northwest garden. Its crisp texture and slightly bitter flavor make it ideal for salads, wraps, and even grilling. Plus, the satisfaction of harvesting your own fresh lettuce, grown in our cool nights and mild summers, is hard to beat.

While we enjoy relatively mild summers, our springs can be slow to warm up, and we sometimes struggle to get enough consistent heat for certain crops. However, with a little planning and attention to timing within our 162-day growing season, you can easily enjoy a bountiful harvest of Romaine lettuce.

Starting Romaine lettuce indoors can give you a head start, especially with our sometimes cool springs. Start your seeds indoors from mid-March through early April, about four weeks before you plan to transplant them outdoors. Use seed trays or small pots filled with a good seed-starting mix.

Keep the trays in a warm location, around 65-70°F, and provide plenty of light. A simple shop light works wonders, or a sunny windowsill if it's bright enough. Bottom watering is your friend here – set the tray in a shallow dish of water and let the soil soak it up to avoid damping off.

Remember, our overcast spring days might mean your seedlings need supplemental light to prevent them from getting leggy.

Transplant your Romaine lettuce seedlings outdoors from mid-April through mid-May, 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 prevents transplant shock.

Space the plants 8-10 inches apart in rows. Even though we have mild summers, a sudden late frost can still happen in April, so keep an eye on the forecast and be ready to cover your seedlings if needed.

Direct sowing Romaine lettuce is also a great option, especially for a continuous harvest. Sow seeds directly into the garden from early April through late July. Direct sowing is easy, but the seeds need consistent moisture to germinate, which can be a challenge if we have a dry spell.

Prepare the soil by loosening it and adding compost. Sow seeds about ¼ inch deep and space them 8-10 inches apart. Thin seedlings as needed to maintain proper spacing.

Romaine lettuce needs consistent moisture to produce crisp, tender leaves. In the Pacific Northwest, our dry summer months mean you'll need to pay attention to watering, but it's not the same as gardening in a hotter climate. Aim for about 1 inch of water per week, especially during the dry summer.

Check the soil moisture by using the "finger test": stick your finger into the soil about 2 inches deep. 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 sometimes humid springs.

Signs of underwatering include wilting leaves and slow growth. Overwatering, on the other hand, can lead to root rot. A layer of mulch, like straw or wood chips, can help retain moisture and keep the soil cool, especially during the warmer parts of the summer.

You can expect your first harvest of Romaine lettuce from early June through mid-October, about 65 days after planting. Harvest outer leaves when they are 6-8 inches long, or harvest the whole head when it feels firm and full-sized. Cut the lettuce just above the soil line.

For a continuous harvest, pick the outer leaves as needed, allowing the inner leaves to continue growing. This will extend your harvest window. As the first frost approaches in early October, harvest any remaining heads to prevent them from being damaged.

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

Bolting in Heat *What it looks like:* A tall flower stalk emerges from the center of the lettuce head, and the leaves become bitter and tough. *What causes it:* Extended warm temperatures, which, although rare, can happen in our PNW summers. *How to fix/prevent it:* Time your plantings for cooler weather, choose bolt-resistant varieties, and provide shade during warm spells. Mulch can also help keep the soil cool.

Aphids *What it looks like:* Clusters of tiny green, black, or white insects on the stems and undersides of leaves. Sticky honeydew residue may also be present. *What causes it:* These sap-sucking insects can multiply quickly, especially during warm weather. *How to fix/prevent it:* Knock them off with a strong spray of water. Encourage beneficial insects like ladybugs. Insecticidal soap can be used for heavy infestations.

Slugs *What it looks like:* Irregular holes in the leaves, especially on low-growing plants. Silvery slime trails are a dead giveaway. *What causes it:* Slugs thrive in our moist conditions, especially in spring and fall. *How to fix/prevent it:* Use beer traps, iron phosphate bait, or diatomaceous earth. Remove hiding spots like mulch and debris. Water in the morning so the soil surface dries out by evening.

Tip Burn *What it looks like:* Brown, dried edges on the inner lettuce leaves. *What causes it:* Inconsistent watering and calcium uptake problems, similar to blossom end rot in tomatoes. *How to fix/prevent it:* Water consistently, avoid fertilizers high in ammonium nitrogen, and ensure good soil calcium levels.

Pacific Northwest Specific Challenges: Our mild summers and dry-summer humidity mean that while bolting can be a concern, it's usually less severe than in hotter climates. Slugs, however, are a constant battle due to our wet springs and falls. Consistent watering is key to preventing tip burn, and choosing bolt-resistant varieties will help you extend your harvest through the warmer months. Late blight isn't as serious of a threat to lettuce, but it's important to be aware of it and practice good garden hygiene.

Companion planting can help your Romaine lettuce thrive. Carrots are good companions because they deter lettuce root aphids. Radishes help repel flea beetles and other pests. Strawberries make a good ground cover and don't compete for resources.

Chives and onions deter aphids and other pests with their strong scent. Avoid planting celery and parsley near Romaine lettuce, as they can attract pests that also target lettuce.