Iceberg Lettuce in Zone 7A — Pacific Northwest

Iceberg lettuce might seem basic, but a homegrown head, crisp and sweet from our cool nights, is a different experience than what you find at the store. It's incredibly versatile in salads and sandwiches, and there's real satisfaction in growing your own, especially when you control the quality from seed to table. Plus, in our climate, it's less about battling intense heat and more about smart timing, making it a great fit for the PNW garden.

We do face challenges like slugs and the potential for bolting if we get an unexpected heat wave, but with our 183-day growing season and generally mild summers, you can absolutely succeed with Iceberg lettuce here. Proper planning and a few preventative measures will have you enjoying fresh lettuce all season long.

Starting Iceberg lettuce indoors isn't always necessary in our climate, but it can give you a jump start, especially if you're eager for an early harvest. If you choose to start indoors, aim for early to late March, about four weeks before you plan to transplant. This allows the seedlings to get a good head start before the still-cool spring weather sets in.

Use seed trays or small pots filled with a good seed-starting mix. Keep them in a warm spot (around 65-70°F) and provide plenty of light, either with a grow light or a very sunny windowsill. Bottom watering is ideal to prevent damping off – just set the tray in a shallow dish of water and let the soil absorb it. Remember, our springs can be overcast, so supplemental light often helps.

Transplant your Iceberg lettuce seedlings outdoors from early April through early May, after they've developed a few sets of true leaves. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the cooler temperatures and stronger sunlight.

Space the seedlings about 12 inches apart in well-drained soil. Be mindful of the weather forecast; a late frost can still happen in early April, so be prepared to cover your transplants if necessary. Those overcast spring days can lull you into a false sense of security!

Direct sowing Iceberg lettuce is a perfectly viable option in the PNW, and it can save you some time and effort. Sow seeds from late March through late July for a continuous harvest. Keep in mind that later sowings will need to be carefully watched for bolting if we get a heat spike in the summer.

Prepare the soil by loosening it and adding some compost. Sow seeds about ¼ inch deep and 12 inches apart. Keep the soil consistently moist until the seeds germinate. Direct sowing skips the transplant shock, but you'll need to be diligent about thinning the seedlings as they grow.

Consistent moisture is key for growing crisp, delicious Iceberg lettuce in our climate. It's more water-sensitive than other lettuce types, and fluctuations can lead to tip burn. Aim to keep the soil consistently moist, but not soggy.

During our wet springs, you might not need to water much at all, but as the dry summer months approach, increase your watering frequency. Check the soil moisture by sticking your finger about two inches deep. If it feels dry, it's time to water. Generally, aim for about 1 inch of water per week, either from rainfall 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 stunted growth, while overwatering can lead to yellowing leaves and root rot. A light layer of mulch, like straw or shredded leaves, can help retain soil moisture and keep the soil cool during the warmer months.

You can expect your first Iceberg lettuce harvest from early June through late October, depending on when you planted. Iceberg lettuce is ready to harvest when the head feels firm and compact, similar to what you'd find at the grocery store. It takes about 70 days from seed.

To harvest, simply cut the head at the base with a sharp knife. This is a one-time harvest, as Iceberg lettuce doesn't regrow like leaf lettuce. As mid- October approaches and the threat of frost looms, harvest any remaining heads, even if they're not quite fully mature. They'll still be delicious, even if a bit smaller.

Here are some common issues you might encounter with Iceberg lettuce in the PNW:

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, 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.

Bolting in Heat

• What it looks like: The lettuce plant sends up a flower stalk. Leaves become tough and bitter. Harvest quality declines.
• What causes it: Extended warm temperatures above the crop's comfort zone.
• How to fix/prevent it: Time plantings for cool weather (spring/fall). Choose bolt-resistant varieties. Provide shade during warm spells. Mulch to keep soil cool. Harvest before bolting progresses.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) 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 knocks them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer (it attracts them).

Slugs

• What it looks like: Irregular holes in leaves, especially low-growing plants. Silvery slime trails on leaves and soil. Damage worse at night and in wet weather.
• What causes it: Gastropods that feed at night in moist conditions. Hide under mulch, boards, and debris during the day.
• How to fix/prevent it: Beer traps (shallow dish of beer sunk into soil). Iron phosphate bait (pet-safe). Remove hiding spots. Water in morning so soil surface dries by evening. Copper tape around beds. Diatomaceous earth around plants.

Pacific Northwest Specific Challenges: Our mild heat and dry-summer rainfall patterns mean that bolting is less of a concern than in hotter climates, but inconsistent watering can still lead to tip burn. Slugs are an ever-present threat, especially during our wet springs, so be vigilant with your control methods. Late blight is not a direct threat to lettuce, but it's important to practice good garden hygiene to prevent its spread to other susceptible plants like tomatoes and potatoes.

Companion planting can help your Iceberg lettuce thrive. Carrots are good companions because their scent deters lettuce root aphids. Radishes break up the soil, making it easier for lettuce roots to grow. Strawberries provide ground cover and help retain moisture. Chives and garlic are natural pest repellents, keeping aphids and other insects away.

Avoid planting Iceberg lettuce near celery and parsley. Celery competes for nutrients and water, while parsley can attract certain pests that also affect lettuce. By choosing the right companions, you can create a healthier and more productive garden.