I've got this lettuce, similar to the red leaf, ruffly variety. It seems to grow only during summer and autumn. I can't coax it into sprouting from the seeds I harvest at any other time of year, which is pretty disappointing as I really want to have part of my salad greens come from my garden. Halp. Edit: I live in the center of Mexico, where climate is warm, hot and dry during the day but cools down quite a bit when the sun sets (desertic and semi-desertic environment). Spring is very dry, summers "moisten" towards the end, autumns are the middle ground between hot-cold and dry-wet, and finally, winters are quite cold, with a hail or two per year. Overall, low natural humidity. My lettuce plants are outside, although I also want to know if growing veggies inside is an option.
Yes, you can do it. In fact on market in present days, we see lettuce all year around.
How? It depends on where you live. @b.nota wrote about artificial light, but this is needed only if you live very north, and for sure Mexico do not have such requirement.
To do it, you may need a green house, or an hotbed, especially for the seedlings. You may generate seedling all months. Depending on the climate, you may keep the lettuce on open field. Maybe with right soil preparation: on some place, stones are used to keep day heat for night, on other maybe just hay, Now it could be simpler just to use some plastic to keep heat during night. You may experiment some methods.
As Bamboo wrote in comment, also the variety could help (and could remove the "greenhouse/plastic" requirement).
Note: "lettuce all year" is possible, but it is also more "professional" type of gardening: it requires some more tools (e.g. plastic cover), but also more control on fertilizers (your soil will never sleep), and more control on diseases and insects/birds (they will learn soon where there is good salad all year around).
From your climate, I think you may plant in autumn the last seedling, and many lettuce varieties should survive your winter, without much extra care. I think the problem is for the late winter and early spring (so preparing and keeping the seedlings on late autumn, early winter), and keeping the young plants from freezing.
I recommend you to ask this group also for alternative vegetables (e.g. arugula, spinach, Swiss chard, etc could be used in similar way, but they have less requirements on winter heat/light)
In winter time you can grow lettuce indoors using artificial light. For lettuce both LED or T5 light will work. Here an example on youtube.
Edit. Okay for Mexico maybe artificial lights are not necessary. I was assuming a temperate climate.
Much as others have said, to grow lettuce year-round you'll probably have to use a temperature-controlled greenhouse, or else grow the lettuce indoors. Or do different things different times of the year.
If you don't like the idea of that, my advice to you is to grow other kinds of greens that taste like lettuce, too, but that have a bigger harvest window (not necessarily all year long, but much longer than lettuce). The closest taste to lettuce I've found in a green might surprise you (but the plants are related; so, it makes sense they might taste similar): Mary thistle (Silybum marianum). Let me explain how to use it:
- Grow it in an at least partially shaded area. The sunnier the location, the more prickly, crinkly, firm, and hard-to-use the leaves will be. In the right light, they're closer to the shape of horseradish leaves.
- You can eat the leaves young, or let them grow huge and cut out the veins. The veins get fibrous, but the rest of the leaf is quite tender, even when large. The veins are easy to remove.
- When harvesting large leaves, use scissors to cut the prickly perimeter of the leaf off. It's pretty easy, as long as the plant wasn't in full sun (if it was in full sun, it'll be hard to avoid the prickles during harvest and when you're preparing the leaves).
Mary thistle leaves are checkered green and white, and very ornamental. Be sure to read up on any interactions they might have with any medications you're taking, or conditions you might have.
Mary thistle is supposed to be a bienniel.
Other plants that taste like lettuce probably exist, too. So, I recommend investigating. It's more common to find those that taste more like spinach or cabbage, though.
Chicory tastes like lettuce before it gets bitter (in the early spring), but although it's easier to grow than lettuce (in my opinion), the non-bitter season for it isn't longer than the lettuce season. If you like the bitterness, you can eat it during the whole frost-free growing season. Also, check out other chicory relatives and derivatives: endive, puntarelle, radicchio, radichetta, sugarloaf, and witloof. I'm not sure if they taste like regular chicory or not. Regular chicory is a perennial.
If you don't mind other flavors, and just want tasty greens, I might recommend trying the greens of these plants: Kale, collards, chard, and kohlrabi (kohlrabi is not known for its greens, but they're exceedingly delicious, and the flowers are even better). Some of these are rather cold hardy. Some grow very well in hot weather.