Lettuce is a delicious veggie with varieties that grow all year round, but like many other veggies, the seeds should be started indoors. This is true of head lettuce especially since it has a low germination success rate.
Once the seeds have sprouted, you should plan for the delicate process of transplanting the seedlings.
When should you transplant lettuce seedlings? You need to be patient with lettuce seedlings and only transplant them when they’re between 4 and 6 weeks old. By that time, each seedling will be between 2 and 3 inches long. Harden the seedlings off before transplanting them to reduce the shock and increase the chances of success.
To say that lettuce is finicky is an understatement. The veggies with all their varieties require careful planning and constant care to keep them growing healthily. Read more to find out the best time to transplant lettuce seedlings.
6 Things To Check Before Transplanting Lettuce Seedlings
Since transplanting lettuce seedlings is a process fraught with risks, you should make sure that the seedlings are of the right age and height before you transplant them. The weather also plays a major role in the success or failure of the lettuce crop.
The following is a checklist of 6 conditions that your lettuce seedlings have to satisfy.
1. Number of True Leaves
Once the lettuce seedling has developed its first set of true leaves, that’s the time to transplant it. Don’t delay the process any longer since the older the lettuce gets, the harder it is for the plant to get over transplantation shock.
You should know the difference between true leaves and seed leaves. The first leaves that emerge from the sprouting seedling are seed leaves. The plant uses the resources in the seed to develop them.
Once the roots have developed long enough to get nutrients and moisture out of the soil, the first set of true leaves emerge.
2. Age of Seedlings
Lettuce is known for its slow growth rate in the early stages of its life. That’s because the roots take their time to develop. Once the root ball reaches 2 to 3 inches long, the veggie starts to grow at a faster rate.
Usually, you’ll wait between 4 and 6 weeks after germination before you consider transplanting the seedlings.
The right age for transplanting the lettuce seedlings depends on the variety. Some varieties take longer than others to develop their root ball and become ready for transplantation without damaging the roots or stunting the growth of the lettuce.
3. Seedling Height
On average, the lettuce seedling shouldn’t exceed 3 inches at the time of transplanting it, but it would take the seedling up to 6 weeks to reach that height, and you likely won’t wait that long.
Don’t try to transplant a young sprout that’s less than 2 inches long. Its root system is still not developed, and there’s a high chance the seedling won’t take in the garden.
4. Deep Freezes Are No Longer a Threat
Freezing is always a threat to most veggies, and this applies to lettuce seedlings that you have germinated indoors. While lettuce seedlings usually survive a light frost, a prolonged or heavy frost may prove fatal.
Allow about 2 to 3 weeks after the last frost is over for the weather to warm up and the chances of any chilly weather to be minimal. Only then should you prepare the soil for the lettuce seedlings to transplant to the garden.
5. Well-Developed Root System
The root system of the lettuce takes the longest time to grow just a couple of inches. While the crown is developing leaves from the resources in the seed, the roots take between 4 and 6 weeks to grow 2 to 3 inches.
This is the ideal development for the roots before you transplant the seedlings. If you allow the seedlings to stay any longer, the roots will grow aggressively and become harder to transplant.
6. Seedlings Have Been Hardened Off
Like many other plants that were started indoors, lettuce seedlings need to be hardened off to ease the shock of transplanting.
This involves taking the seedling outdoors for a limited number of hours 7 to 10 days from the time you want to transplant them. That way, the seedlings will establish quickly and won’t have stunted growth.
What Temperature Is Too Cold for Lettuce?
As a cool-season veggie, lettuce can handle cold temperatures and even the occasional light freeze at night, but if the cold temperature persists night after night, the plant will show signs of stress. If the temperature drops below 25℉, the plant will start to freeze over.
Ice forms inside the tissue of the stems and leaves causing cracks to appear. Even if the weather warms up and the icy stem and leaves melt, chances are the plant will die immediately after that.
Thinning Lettuce Seedlings
As with other veggies, you need to start more lettuce seeds than you actually need. This ensures that you get the right number of seedlings. You should also transplant all the seedlings because you can never tell how many of those seedlings will take. Then you can thin them out.
Thinning lettuce seedlings should be done in two phases. That way you’ll avoid disturbing the soil and exposing the roots of the healthy plants more than necessary.
Allow one week after the first time you thin the lettuce seedlings. Then come back to pull out more seedlings and achieve the right spacing.
How To Harden Off Lettuce Seedlings
To harden off your lettuce seedlings and improve their chances of success, follow these steps.
- Start hardening off the seedlings 7 to 10 days before you plan to transplant them.
- When the air temperature is above 55℉, take the seedlings outside.
- Place them in a spot that gets partial shade and is sheltered from strong winds.
- Keep the seedlings outdoors for just one hour on the first day, and then take them back inside.
- On the second day, place them in the same spot for 2 hours.
- Increase the number of outdoor hours by increments of one hour every day.
- On the last day before transplanting, keep the seedlings outside all day, and take them inside in the evening.
- Transplant the hardened lettuce seedlings the next day.
How To Transplant Lettuce Seedlings
While the lettuce seedlings are being hardened off, you can start preparing the planting bed. The process is as delicate as can be since lettuce seedlings are sensitive to transplant shock even when hardened off. Here are the necessary steps.
- Select a spot that gets 6 to 8 hours of sunlight every day.
- Clear the planting bed of any debris, fallen leaves, or weeds. Lettuce plants don’t like competing over resources.
- Till the top 12 inches of the soil, and mix in a 3-inch thick layer of organic compost. Rake the planting bed well, and let it sit for a few days under the sun.
- When the lettuce seedlings are ready to transplant, water the medium in the tray to make it easier to extract the seedlings.
- Gently take out the seedling with a clump of wet soil around the roots.
- Dig a hole in the planting bed as deep as the distance from the tip of the root ball to the soil mark on the stem.
- Place the seedling into the hole, and gently backfill with soil.
- Repeat with the rest of the seedlings.
- Water the planting bed thoroughly to help the seedlings settle.
When planting lettuce in rows, the spacing is crucial for the success of the veggies. For head lettuce, the rows should be 12 to 18 inches apart, and each lettuce plant should be 10 to 12 inches from the next one.
As for leaf lettuce, the rows should also be 12 to 18 inches apart, but the lettuce seedlings should only be 4 inches apart.
Can You Replant Thinned Seedlings?
You can replant thinned lettuce seedlings as long as the root system is intact and the seedlings haven’t been left out in the open for too long.
How Long Does Lettuce Take To Grow From Seed?
The majority of lettuce varieties will reach maturity within 6 to 14 weeks from the time you plant the seeds. Some varieties reach harvest size faster than others.
You should transplant lettuce seedlings between 4 and 6 weeks after germination. Start hardening off the seedlings 7 to 10 days before transplanting them.