Tips for Growing Lettuce Indoors

Branching Out

Deeply Rooted
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I have started two large batches of leaf lettuce seedlings over the course of the past month, and while I am having good results getting them started I ran in to a bottle neck with my first batch now that the seedlings are about 3-4 weeks old. The lettuce seedlings are developing a broad habit, and become crowded in the large 4-cells that I had used to bump them up. A friend got a fancy cold frame for Christmas, so she took a couple of dozen off my hands thankfully. I will have to move the rest of them to individual 4" pots, which will require a lot of potting soil.

Round two of lettuce seedlings were started in 3/4" mini soil blocks, and are just one week old. This time I selected four kinds of Romaine in the hopes that it will have a more slender upright growth habit. I am going to try bumping them up to the 2" soil blocks this time, so that I can space the lettuce blocks 5-6" apart on a tray to grow them out under lights. It is my hope that this will help with the crowding, but it will take up a lot of space. It will also be interesting to see if a 2" block of soil is sufficient to sustain them to grow to a reasonable size without having to bump them up again. The plan is to be able to harvest the outer leaves so that the rest of the plant can keep growing, so I suspect that I will need a large number of plants.

In looking through past threads on this topic I noticed that most of the posts were from long, long ago. Just curious if anyone has had success producing robust quantities of lettuce indoors recently. Any tips would be most appreciated.
 

ducks4you

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In my experience starting indoors, it was on the porch shelf in April.
My studies suggest that EVERY seed wants heat to germinate. Elios Coleman starts his winter crops in October/November, while it is still warm, then they grow VERY SLOWLY with not the best sunlight, but in cold temperatures without ice.
Therefore, I would start ALL vegetable seeds in a warm place or on a heat mat with the best light. If you have a south facing window and can use a ledge or a small table you could start them there.
 
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heirloomgal

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I've never tried indoor lettuce @Branching Out but I do know that when I set out those wee transplants in late May, it pained me to see all that empty space around them. I needed to give them the full amount of space for full maturity & seed saving and by Sept they took up all that space. I wonder if leaf lettuce like Black Seeded Simpson might be another option, simply because people tend to grow it crowded anyway and that probably helps limit the size they get when planted as a single?
 

Dahlia

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I have started two large batches of leaf lettuce seedlings over the course of the past month, and while I am having good results getting them started I ran in to a bottle neck with my first batch now that the seedlings are about 3-4 weeks old. The lettuce seedlings are developing a broad habit, and become crowded in the large 4-cells that I had used to bump them up. A friend got a fancy cold frame for Christmas, so she took a couple of dozen off my hands thankfully. I will have to move the rest of them to individual 4" pots, which will require a lot of potting soil.

Round two of lettuce seedlings were started in 3/4" mini soil blocks, and are just one week old. This time I selected four kinds of Romaine in the hopes that it will have a more slender upright growth habit. I am going to try bumping them up to the 2" soil blocks this time, so that I can space the lettuce blocks 5-6" apart on a tray to grow them out under lights. It is my hope that this will help with the crowding, but it will take up a lot of space. It will also be interesting to see if a 2" block of soil is sufficient to sustain them to grow to a reasonable size without having to bump them up again. The plan is to be able to harvest the outer leaves so that the rest of the plant can keep growing, so I suspect that I will need a large number of plants.

In looking through past threads on this topic I noticed that most of the posts were from long, long ago. Just curious if anyone has had success producing robust quantities of lettuce indoors recently. Any tips would be most appreciated.
I've never grown lettuce indoors. However, I read about someone who used a hydroponic method to grow lettuce indoors in 4 ounce plastic bottles! I believe they used the "Kratky" method. It sounded very low maintenance and cheap to do!
 

Branching Out

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I've never tried indoor lettuce @Branching Out but I do know that when I set out those wee transplants in late May, it pained me to see all that empty space around them. I needed to give them the full amount of space for full maturity & seed saving and by Sept they took up all that space. I wonder if leaf lettuce like Black Seeded Simpson might be another option, simply because people tend to grow it crowded anyway and that probably helps limit the size they get when planted as a single?
I am definitely seeing a big difference in the spread between some of the varieties that are sizing up, so finding just the right cultivars may well be an important piece of the puzzle. I will put Black Seeded Simpson on the list-- thank you!
 

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I've never grown lettuce indoors. However, I read about someone who used a hydroponic method to grow lettuce indoors in 4 ounce plastic bottles! I believe they used the "Kratky" method. It sounded very low maintenance and cheap to do!
Kratky will be worth considering. I just watched a couple of video on this method, and while I am not sure that I want to go a 100% hydroponic route it still amazes me that plants can be grown this way, without any soil at all. Which leads me to think that a 2" soil block could indeed be sufficient as long as enough nutrients reach the lettuce plants. There may be a hybrid version that I could do, involving lettuce in soil blocks on a wide-weave plastic mesh tray that sits above a tray of nutrient rich water; will have to give that some thought. By the way, my friend has an indoor water-based system on her kitchen counter in her condo, and she is growing circles around me.
 

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In my experience starting indoors, it was on the porch shelf in April.
My studies suggest that EVERY seed wants heat to germinate. Elios Coleman starts his winter crops in October/November, while it is still warm, then they grow VERY SLOWLY with not the best sunlight, but in cold temperatures without ice.
Therefore, I would start ALL vegetable seeds in a warm place or on a heat mat with the best light. If you have a south facing window and can use a ledge or a small table you could start them there.
I save a lot of lettuce seed each year, and it seems to germinates really fast--- usually in just 3-5 days if I set the trays in the living room with a humidity dome. The very second I see a sprout I move them under lights or they seem to stretch quite dramatically. Germinating them primarily under lights seems to produce a nice low, stocky seedling.
 

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My quest to find a cost effective and space saving way to grow lettuce indoors continues. The past two days have been spent trying out my new 2" soil blocker for bumping up tiny little 3/4" cubes of 2 week old lettuce seedlings. First up was Buttercrunch lettuce, which is frequently recommended for growing indoors. It is crazy how the roots have developed already, and bumping them up to the large block is an absolute dream. While I sifted ProMix potting soil for the tiny blocks, I am using ProMix HP straight from the large bale for the larger blocks (steamed in the oven for a bit first, to make sure I am not bringing in fungus gnats from outdoors). Hopefully the blocks will hold together nicely once the lettuce roots fill in. Given that the fresh blocks are rather fragile I will bottom water them, and place them under lights.
 

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Branching Out

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Bumping up the one month old lettuce was not nearly as much fun, as I needed a LOT of potting soil and it was kind of messy and fiddly too. Some of the seedlings had completely outgrown the good sized 4-cells that I had them in, so they each got their own 4" pot. It was quite interesting to see the variation in growth from one cultivar to another. My lettuce hero Frank Morton recommends growing different kinds of lettuce side by side so that you can really compare them, and I can now see that this is a very good idea. The bright chartreuse green leafy one is from seed that I have been saving for years, and it is almost twice the size of the diminutive and slow growing Lolla Darki with tightly curled red leaves.
 

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The difference in size between 2 week old lettuce (top left) and 4 week old lettuce (bottom right) is astonishing. Clearly now that the one month old lettuce are in 4" pots I will have to be creative in finding space for them. My thought is to divide the group in two, so that I can put half of them under lights and move the other half of the pack outdoors for hardening off. Then midday I will do a swap, so the ones from inside go outside and the others go back under lights indoors. (And yes, I must be crazy. Or enthusiastic. You be the judge). Once the lettuce are completely hardened off a bunch will go to friends and neighbours, for Phase 2 of this experiment: how to keep lettuce alive outdoors in January.
 

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