Iceberg Lettuce in Zone 7B — Pacific Northwest

Iceberg lettuce gets a bad rap sometimes, but there's nothing quite like the crisp, cool crunch of a homegrown head on a summer sandwich. Plus, our cool nights here in the PNW actually enhance the sweetness, so you get a flavor that store-bought iceberg just can't match. It's incredibly satisfying to harvest a beautiful, tightly packed head of lettuce from your own backyard.

Growing Iceberg in the Pacific Northwest does present a few challenges, mostly related to our cool springs and the potential for a quick bolt when the weather warms up. But with a little planning and attention to timing, you can definitely enjoy fresh Iceberg from your garden throughout our generous 193-day growing season.

Starting Iceberg lettuce indoors is an option, especially if you're eager for an early harvest, but it's not essential. Our springs are often overcast, so seedlings may get leggy indoors without supplemental lighting. If you choose to start indoors, aim to sow seeds from late February through mid March, about four weeks before you plan to transplant.

Use seed trays with a good seed-starting mix, and keep them in a warm location, ideally around 65-70°F. A heat mat can help with germination. Bottom watering is a great way to keep the soil consistently moist without overwatering, which can lead to damping off.

Transplant your Iceberg lettuce seedlings outdoors from 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 helps them adjust to the cooler temperatures and stronger sunlight.

Space your plants about 12 inches apart to give them plenty of room to develop those large heads. Be prepared for some cool, wet weather during this time; row covers can provide extra protection if needed.

Direct sowing Iceberg lettuce is perfectly feasible in the Pacific Northwest, and it can save you some effort. Sow seeds from mid March through early August for a continuous harvest.

Prepare your soil by loosening it and adding some compost. Lettuce seeds need light to germinate, so sow them shallowly, about ¼ inch deep. Keep the soil consistently moist until the seedlings emerge. Thin the seedlings to about 12 inches apart once they're a few inches tall.

Consistent moisture is key to growing great Iceberg lettuce in our climate, even though we have dry summers. Unlike some other types of lettuce, Iceberg is more sensitive to drying out, which can lead to tip burn and other problems.

During our wet springs, you may not need to water much at all, but once the dry summer months arrive, check the soil moisture regularly. Stick your finger about 2 inches deep into the soil; if it feels dry, it's time to water. Aim for about 1 inch of water per week, adjusting based on rainfall. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our humid (dry-summer type) conditions.

Signs of underwatering include wilting and stunted growth, while overwatering can lead to yellowing leaves and root rot. Applying a layer of mulch, like straw or shredded leaves, can help retain moisture and keep the soil cool during the warmer months.

You can expect your first harvest of Iceberg lettuce from late May through early November, 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 generally takes about 70 days from planting.

To harvest, simply cut the head at the base with a sharp knife. Once you cut the head, it won't regrow, so it's a one-time harvest.

As the first frost approaches in late October, harvest any remaining heads, even if they're not quite fully mature. They won't survive a hard freeze.

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

Tip Burn

• What it looks like: Brown, dried edges on the inner lettuce leaves. In severe cases, it can affect the outer leaves too.
• What causes it: A calcium uptake problem caused by inconsistent watering, similar to blossom end rot in tomatoes. High temperatures worsen it.
• How to fix/prevent it: Water consistently to maintain even soil moisture. Avoid fertilizers high in ammonium nitrogen. Ensure your soil has good calcium levels. Choose tip burn-resistant varieties, and provide shade during warm spells.

Bolting in Heat

• What it looks like: The lettuce plant sends up a flower stalk. The leaves become tough and bitter, and the harvest quality declines.
• What causes it: Extended warm temperatures above the crop's comfort zone. Lettuce bolts when days consistently exceed 80°F.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells. Mulch to keep the soil cool. Harvest the lettuce before bolting progresses too far.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on the stems and undersides of leaves. There might be a sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects. Their populations explode in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: Use a strong spray of water to knock them off the plants. Encourage ladybugs and lacewings, which are natural predators. Apply insecticidal soap for heavy infestations. Neem oil can also work systemically. Avoid excess nitrogen fertilizer, as it attracts aphids.

Slugs

• What it looks like: Irregular holes in the leaves, especially on low-growing plants. Silvery slime trails on the leaves and soil. Damage is worse at night and in wet weather.
• What causes it: Gastropods that feed at night in moist conditions. They hide under mulch, boards, and debris during the day. Our wet springs and mild, moist conditions make this a common problem.
• How to fix/prevent it: Use beer traps (shallow dishes of beer sunk into the soil). Apply iron phosphate bait (which is pet-safe). Remove hiding spots like boards and debris. Water in the morning so the soil surface dries out by evening. Put copper tape around beds. Sprinkle diatomaceous earth around the plants.

Pacific Northwest Specific Challenges: Our mild summers rarely see temperatures above 90°F, which is a big advantage for growing Iceberg. However, our dry-summer humidity and rainfall patterns mean you need to be vigilant about consistent watering to prevent tip burn. Slugs are also a constant threat, especially during our wet springs, so be proactive with your slug control measures. We don't need to worry about late blight on lettuce.

Companion planting can be a great way to improve the health and productivity of your Iceberg lettuce. Carrots make excellent companions because they deter lettuce root aphids. Radishes are also beneficial, as they attract flea beetles away from the lettuce. Strawberries can act as a living mulch, keeping the soil cool and moist.

Chives and garlic are great because they repel aphids and other pests with their strong scent.

Avoid planting celery and parsley near Iceberg lettuce. Celery competes for nutrients, and parsley can attract some of the same pests that bother lettuce.