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Grow salad greens indoors all winter long under inexpensive shop lights | The Old Farmer's Almanac

Grow Your Own Salads Indoors All Winter

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Growing Lettuce Indoors Under Lights

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You might not think it’s possible to grow salad leaves during the depths of winter, but it is! Seriously, it’s not that hard because lettuce and greens are perfect for growing in containers—plus, no weeds or pests! Learn how to grow fresh, homegrown leaves even in the coldest months.

This project is a great opportunity to repurpose those polystyrene (both foam and transparent) containers. These are always good to collect for starting spring transplants. Or you could use old plastic or wooden fruit crates; you’ll just need to line the sides with a couple sheets of newspaper or weed fabric since the sides aren’t solid. Wider containers are better because they will give more space between plants and more growing medium for the roots to explore. 

All of the salad greens I plant will grow well in a variety of places:

  1. Grow in a cold frame outside.
  2. Grow under cover in the greenhouse.
  3. Bring trays indoors to grow under grow lights.

Growing Lettuce Under Lights

Last year, I purchased grow lights to start seedlings in early spring. They’ve never been used in winter so growing salad in winter is a perfect match!

If you don’t have grow lights, you just need cheap fluorescent shop lights. My fixture is suspended by chains and S-hooks from the ceiling of my living-room alcove. (You could also put the grow lights in an upstairs bedroom since heat rises.)  

It is not necessary to invest in the very intense lighting systems that hydroponic growers use, because vegetable and herb seedlings live indoors for but a few short weeks, and regular florescent lights are ample for their needs. Besides, once seedlings are up and growing, gradually exposing them to more sunlight is the best way to prepare them for life in the garden.

Ideally, you want the light to be less than 2 inches from the tops of plants, but some seedlings gain height faster than others. Raising the slower growers by placing them atop books or boxes is often the easiest way to get them closer to the light they crave. 

Filling the Containers With Potting Mix

You’ll want to fill the trays. I like a mixture of half soilless sterile potting soil suitable for seeds and half compost. But you could also just use all-purpose potting mix. 

Push the potting mix into corners to get a really good fill. Well-filled trays mean more for the roots to explore, and ultimately this makes for stronger plants. Shake and tap to level and settle the potting mix once the trays are filled.

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Photo: Margaret Boyles

Which Salad Greens To Plant?

The simple answer: almost any type of salad or cooking greens—the faster-growing the better—and leafy herbs.

During my first experiments, I mixed together seeds left over from my spring–summer garden and simply divided into 3 trays based on comparable germination times. Over time, I’ve added new leaves. 

  • Winter Lettuce: Oak-leaf lettuce and various leaf lettuces provide the perfect base to any salad. They also work well for cut-and-come-again harvesting where you can remove a few leaves every week, extending production over a longer period.
  • Asian Greens, Arugula, and Mustard: Mizuna is one of my favorite Asian greens for salads, producing a contrasting feathery texture, a mild peppery tang, and nutrition. It’s great in stir-fries, too. Arugula is a delicious leave which also offers a peppery taste. Mustard has a complementary warming flavor with colorful leaves to pretty up salads.
  • Winter Purslane: Also called miner’s lettuce of Claytonia, this super-hardy winter green has lush, almost juicy leaves with a smooth, mild taste. 
  • Mâche: This green, also known as corn salad or lamb’s lettuce, is another mild leaf that’s also one of the most prolific. Expect lots of leaves to form the bedrock of any winter salad.
  • Pea Shoots: Hardy varieties of pea shoots promise that sweet, super-fresh pea taste in leaf form. Totally delicious and well worth growing! Not only good in salads, they also add a fresh taste of peas as a garnish on warming soups, such as those made from winter squash. Once they’re 8 to 10 inches tall, harvest the top few inches so they keep sprouting!
  • Mesclun: If you’re buying new seeds for winter planting, I suggest one of the fast-growing mesclun or braising mixes (also called stir-fry mixes) sold by most seed companies.I scattered the seeds thickly across the soil surface, covered them with a bit of compost, and watered them well with a small watering can.

Herbs: I also planted a few seeds each of basil, parsley, and cilantro in smaller, separate containers.

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Credit: Margaret Boyles

Planting and Growing Winter Greens

Follow the directions on seed depth and distance. With containers, do not crowd. Air circulation is important and the roots need room to explain in the container since they don’t have limitless ground soil. After everything is sown, it’s time to give them a good water.

To water, we recommend a simple watering can fitted with a rose. Just water back and forth a few times to soak the potting mix. Leave them to drain off.

Once the seeds germinate, I turn the lights on when I get up each morning and shut them off around supper time. I watered them every couple of days, when the top of the planting medium felt dry. Every week to 10 days, I watered with a weak solution of seaweed and fish emulsion (available at garden stores).

It’s important to keep the seedlings well watered and use high-quality compost or amendments to supply ample nutrients. 

Equally important is thinning out the plants. I started thinning the plants as soon as they’d developed two or three sets of leaves, about three weeks after germination. I cut out any plants that were closer than an inch apart, snipping the plants just above soil level (to avoid disturbing neighboring seedlings), rinsing them, and tossing them into soups and cabbage salads.

As the plants grew bigger, I harvested the outer leaves and left the rest to grow. Alternatively, you can clip greens from throughout the whole container with fingernail scissors, making sure to leave the growing tips to produce another crop.

Be sure to raise your lights so that the plants do not get scorched. As a general guide, lights should be kept 4 inches above the highest leaf.

After 5 weeks of growth, six to eight containers of greens began producing robust, two-person salads three or four times a week for about 6 weeks, as well as quite a few handfuls of greens to toss into our frequent winter soups.

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Photo: Margaret Boyles

By the way, producing winter salad greens under lights makes a wonderful project for children of any age. Great science project possibilities, too. Plus, there aren’t any weeds or critters eating your greens!

The alcove where I keep my containers is also home to my stationary bike, which I ride almost every day or evening all winter long. Good food and good exercise: What a combo!

Video on Starting Winter Lettuce and Greens in Trays

To learn more, our colleague Ben demonstrates how he starts his lettuce leaves in trays in the autumn to enjoy a little piece of summer green in the cold, dark days of winter!

See the Almanac’s Growing Guides for vegetables and herbs.

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