Starting lettuce from seed *(re-purposing plastic tofu containers)

Red Iceberg Lettuce - a summer rose!

This post gives generic information for starting cool-weather crops (lettuce, cabbage, broccoli, kale etc) from seed.

 

Note: Though this was originally written and posted in 2011, and some of our practices have shifted (for example we no longer use rabbit manure - or any animal by-products - in our garden or soil-mix - LINK: Making Your Own "Veganic" Potting Soil in Your Greenhouse Paths - Using Worms) - the core of the information is still accurate and useful so we have republished with minimal editing...

 

Here at the Sharing Gardens (in the Pacific NW) we have several ways of starting seeds. This post is about starting them in a grow-tunnel or greenhouse using re-purposed tofu containers to get them started. (To read about Starting Seedlings Directly in Greenhouse Raised Beds - click here).

We're vegetarians and end up with a lot of these white, plastic, square tofu containers. We've found they make great tubs to start small seedlings. We drill holes in the bottom for drainage and fill with a finely sifted, moist, organic potting mix.

This method presumes you have a greenhouse though it doesn't need to be very big. Seedlings will need sun and protection from wind and severe cold once they have germinated. In 2010, we started everything we needed for three 50 x 50' garden-beds in an 8'x10' greenhouse (below). We just had to time everything so that the first seedlings that were less cold-sensitive (lettuce, peas, cabbage etc.) could be brought outside in time for the hot-weather crops (tomatoes, peppers, melons etc.) to be started inside.

Of course if you have a much larger greenhouse, you can start many more seedlings!

In 2010 we started everything we needed for three 50 x 50' garden-beds in this cozy, little 8'x10' greenhouse. We just had to time everything so that the first seedlings that were less cold-sensitive (lettuce, peas, cabbage etc.) could be brought outside in time for the hot-weather crops (tomatoes, peppers, melons etc.) to be started inside.

First step - Soil: In the early days of the Sharing Gardens we purchased soil by the trailer-load. We chose an organic soil that didn't have any nutrients added, and added an organic fertilizer. We mixed up batches in a wheelbarrow. Later, once we were more established, we began to make our own potting mix but most people don't have that capacity. Just be sure you use 'organic' potting mix from a reliable source.
 

In the early days, we bought organic soil by the trailer-load and added commercially-made fertilizer. Now, we make our own. Making Your Own "Veganic" Potting Soil in Your Greenhouse Paths - Using Worms

Sifting Soil: The key here is that, if your potting mix has large chunks of organic matter, your seedlings will struggle to grow. We sift our soil through a nursery flat with tiny holes to remove all large chunks.

We use a nursery-flat to sift our potting mix. This gets rid of larger chunks of material that would make new seedlings struggle to grow.

Be sure your soil is moist, but not wet. Fill with a good potting mix, using the bottom of another tofu tub to pack the soil firmly and make a flat surface for the seeds. This is important as, if the soil level is uneven you will get varying germination-times for your seedlings. You want them all to come up at once.

Planting seeds: After misting the soil so it is good and damp, we sprinkle the seeds with our finger-tips trying to distribute them evenly and not too thickly. If the are planted too densely, it's hard to tease them apart when you transplant them to larger pots.  

 

Seedlings germinating in re-purposed tofu containers. We try to sprinkle them evenly and not-too densely.

 

Lastly we gently sprinkle a thin lay of cover soil over the seeds and lightly mist to settle the seeds. They must be kept moist but not overly wet or the seeds and starts may rot. Lettuce and brassica seeds germinate best in a cool soil so you shouldn't need to put it on a heat mat or under a lamp to get it to germinate. If you do apply bottom heat, check seedlings frequently so they don't dry out.

 

Chris and Donn transplanting seedlings into tofu containers; six to a 'pot'.

When the seedlings are about 1/2" - 1" (2 cm) high, they are ready for transplanting. We put ours in regular or "jumbo" six-packs, or in the same tofu-containers (six to a container). We use a basic, organic potting soil and add our own fertilizer. To each wheelbarrow of soil we add about two cups of all-purpose organic fertilizer and about a half-gallon of sifted rabbit manure. (Note 2025: We now make our own potting mix from the compost 'harvested' in our greenhouse paths, wood-ash and perlite: Making Your Own "Veganic" Potting Soil in Your Greenhouse Paths - Using Worms). For the Sharing Gardens, where we might grow 1,000 or more lettuce plants per season, transplanting is done in large batches. Being systematic in the nursery will save you time and materials and you will have much better results. Have labels ready so you keep track of the varieties you are transplanting. 

 

Being systematic in the nursery will save you time and materials and you will have much better results.

Fill a flat of six-packs (or tofu containers) with soil and mist them with water. Wet soil is less shocking to transplanted roots than dry. 

 

Adri, filling 6-packs with soil. A fun, relaxing job, at any age!

Using your finger, a stick or some other object, make a generous hole in each of the cells of the six-packs (or whatever you're planting into).

Lettuce seedlings in a tofu container. Using a pen to make holes for transplants.

To remove seedlings for transplanting: Cupping your hand over the whole tofu-tub of seedlings, flip it over and tap the bottom, catching the whole clump of soil and seedlings in your hand. Gently flip it back over and place it on a tray to catch the loose soil as it drops off.

 

From the tray, pull off a clump of seedlings and, holding them by their leaves, tease apart a single plant with its roots. 

 

It is very important that all the roots go down into the soil and are covered. If they stick out from the surface, this is called 'J-rooting' and  will often kill the plants as they dry out too easily. This is why you want to dig a generously-sized hole so the rootlets don't catch on the sides as you lower them in. After pressing the soil in around each seedling, water them in gently to settle the soil. Label the tray and move onto the next.

Transplanting seedlings. Note: Hold seedlings by leaves, not roots or stems.

Depending on warmth and sunlight, and the size of the six-packs you use, your lettuce will be ready to plant in garden beds in six to ten weeks. If you stagger your plantings it will mean your lettuce doesn't all come ripe at once. Ideally you wait until the root ball has filled the six-pack cell enough to hold the soil as you pop it out, without being totally root-bound (roots coming through the bottom of the six-pack).

A variety of seedlings growing in tofu containers; six to a pot.

 A week or two before you transplant into your garden, bring the starts outside and begin "hardening them off". Put them where they will get plenty of sun but not too much wind. They will withstand a light frost but if it is going to get very cold, or doesn't warm up in the day, bring them back into the greenhouse till conditions improve. During this hardening-off period, prepare garden beds so they are ready to receive transplants. In our "deep-mulch/minimal till" gardens, we pull a row of mulch over to the adjacent path (with a pitchfork) and, with a trowel dig a small hole just the size of the lettuce's root-ball. This leaves worm holes intact and lettuce seems to thrive without any roto-tilling needed.

Seedlings "hardening-off".

Here in our area, slugs can be a real problem in the spring. Follow this link for ideas on how to re-use milk cartons or soy-milk containers to thwart off their feasting: Re-Purposing Things. Here is another way to deal with a slug problem: Organic Solution to Slugs - Iron Phosphate. 

Transplanting peas and lettuce

We don't find that additional fertilizing is necessary for lettuce plants. They receive enough nutrients from the soil. But heavy feeders such as broccoli, cabbage or any of the other 'brassicas' would benefit from added compost or some organic fertilizer mixed in at the site you are planting out your seedlings - just don't use too much or the plants will grow quickly and have thin cell walls making them more susceptible to pests.) 

Several weeks after transplanting. Picking individual lettuce leaves for salad.

We hold off on mulching them because we want the sun to warm up and dry out the soil and mulch provides habitat for the slugs. Sometimes, after the lettuce or other seedlings are well established and the soil is warmed up, we mulch with a few inches of grass clippings around our plants. Ideally, let the clippings dry out for a few days on a tarp or in a bin. Fresh clippings, if piled thickly, can heat up considerably and burn your plants.

Chris Burns with beautiful lettuce harvest! 2011

We plant our lettuce spaced about 6" - 8" (12 - 15 cm) apart (brassicas need more room: 18" seems to work well...). We harvest the lettuce intermittently, giving the remaining lettuce room to grow. In the early stages, before the heads are fully formed, we harvest one to three leaves off each plant, rather than clipping whole heads. As the heads become full-size we harvest by cutting them off at the root with a paring knife, leaving the roots in the ground to feed the worms.

 

We hope this post has helped take some of the mystery out of starting spring crops from seed. If you've been interested in learning to save your own seed, lettuce is one of the easier crops to save seeds from. Here's a post we wrote about the process: LINK: How to Save Your Own Lettuce Seed Enjoy!