Knowing When to Transplant Lettuce Seedlings for a Successful Crop

Lettuce is a cool-season crop that can be grown in spring and fall in most climates. Starting lettuce from seed indoors provides several advantages over direct-sowing outdoors. Transplanting lettuce seedlings at the right time is key for a bountiful harvest. This comprehensive guide will walk you through when and how to transplant lettuce for optimal growth.

Why Start Lettuce Indoors?

Here are some of the top reasons for starting lettuce transplants rather than direct-sowing:

• Earlier harvest Getting a head start indoors allows you to transplant earlier in spring for an earlier harvest This extends the lettuce growing season

• More variety Starting indoors gives you access to a wider selection of lettuce varieties that may not be available as starts You can grow red, green, oakleaf, romaine, butterhead and more.

• Controlled conditions: Indoor seed-starting provides warmth, proper lighting and protection from pests. This leads to higher germination rates and sturdier transplants.

• Better spacing: Transplanting gives you more control over lettuce spacing and arrangement in the garden bed for efficient use of space.

• Seed saving: Allowing a few lettuces to bolt gives you seeds for future harvests.

When to Start Lettuce Seeds Indoors

Lettuce seedlings grow quickly, so seeds can be started indoors 4-6 weeks before the last expected spring frost date. Here are some tips for timing:

• In cooler climates, start seeds 6 weeks before your average last frost to give seedlings time to mature.

• In warmer climates with a longer growing season, 4 weeks may be enough time.

• Stagger planting every 2 weeks for a continuous lettuce harvest.

• Refer to the seed packet for days to maturity so you know how long each variety needs.

• Use a seed starting calculator based on your zip code to determine optimal start times.

Aim to transplant lettuce outdoors after danger of frost when soil temperatures reach at least 40°F.

Providing the Right Conditions for Germination

Lettuce seeds need proper temperature, moisture and light to germinate and grow into strong transplants:

• Soil temperature: Lettuce germinates best at 70-75°F. Use a seedling heat mat if needed.

• Moisture: Keep seeds and seedlings consistently moist but not soaked. Cover trays with plastic to retain moisture.

• Light: Place new seedlings under grow lights or in a sunny window once sprouted. Provide 12-16 hours per day.

• Air circulation: Use a small fan to circulate air once the plastic is removed. This prevents disease.

• Fertilizer: Use a diluted liquid fertilizer or compost tea once true leaves emerge.

How to Transplant Lettuce

Follow these tips for successfully moving lettuce from indoors to the garden:

• Harden off seedlings by reducing water and temperature for 7-10 days. Slowly introduce to outdoor conditions.

• Transplant on a cloudy day or in late afternoon to avoid transplant shock.

• Water soil well before and after transplanting.

• Dig a hole slightly larger than each root ball. Set plant at same level it was growing in the container.

• Space according to variety – 4-12 inches between plants is common.

• Water newly planted seedlings daily until established. Add mulch to retain moisture.

• Provide shade if transplanting in hot weather. Remove shade after a week once established.

What to Look for When Transplanting Lettuce

Use these signs to identify when lettuce seedlings are ready for transplanting:

• Age: Most varieties are ready about 3-5 weeks after germination when they have 2-4 true leaves.

• Size: Seedlings should be 3-4 inches tall with a robust stem and well developed root system.

• Health: Choose stocky, deep green plants without signs of premature bolting or disease.

• Hardened off: Seedlings should be acclimated to outdoor conditions through the hardening off process.

Avoid transplanting leggy, discolored or root-bound plants. These are stressed and less likely to survive and thrive.

Troubleshooting Transplant Shock

Lettuce transplants may experience some shock after transplanting. Here are some common issues and how to resolve them:

• Wilting: Increase watering frequency and use shade to reduce transpiration.

• Poor growth: Check for root issues like girdling or damage. Replant if needed.

• Bolting: Bolting is premature flowering. Control bolting by avoiding transplant stress and extreme temperatures.

• Tip burn: This browning of leaf margins can occur if inadequate calcium reaches leaves. Add dolomitic lime to soil.

• Pests/disease: Inspect for common lettuce pests like slugs, aphids and mildew. Treat accordingly.

With proper timing, conditions and care, transplanting lettuce from indoor starts to the garden can result in a healthy, plentiful lettuce crop. Pay close attention to signs of readiness, cautiously move seedlings outdoors, and address any transplant shock that occurs. With this lettuce transplanting guidance, your leafy greens will flourish!