Try your hand at an indoor winter garden! You can have fresh salad greens year round by growing lettuce indoors.
If you give lettuce what it needs, you can be successful and provide your family with baby greens that will rival those store-bought clam shells of salad greens. Lettuce has different needs than microgreens, so keep that in mind.
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How to grow lettuce indoors
1. Soil depth of four inches
Baby lettuce has a long tap root. They need a deeper pot than microgreens. If you can give them at least four inches of soil depth, your lettuce will have room to grow.
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The deeper one-pound plastic clam shells that organic greens are often sold in are 4″ deep. That’s just the right size container to grow lettuce in.
If you have some of these to recycle, they’re ideal for growing lettuce indoors.
I recommend using a sterilized organic seed potting mix for indoor growing. If you are using a commercial potting mix, add 1/4 cup of kelp meal, and 1/3 cup of worm castings for 1 gallon (16 cups) of potting mix to provide the micronutrients for your growing lettuce.
2. Bright grow lights or bright daylight window
Young lettuce needs a bright, full spectrum grow light, or a very sunny window. If your natural light is dim in winter, provide supplemental lighting for baby greens. The full spectrum grow light should be placed about 4″ above the top of the leaves.
I use lights to grow lettuce indoors in January, when the natural light is lacking.
If you notice the leaves of your baby plants stretching and becoming spindly, lower the light to give adequate light for plant growth or raise the plants to get them within four inches of the light. If they are in a sunny window, this is an indication that they need supplemental light.
Related: Winter Garden Projects to Tackle
3. Organic fertilizer
Microgreens grow to harvest size from the energy inherent in the seed, so soil fertility isn’t as great a concern. On the other hand, baby lettuce leaves require nitrogen and trace minerals for fast growth. Sweet, tender baby lettuce leaves must grow fast to maintain their good qualities.
Liquid kelp fertilizer, worm castings, or compost tea can ensure fast growth in your indoor winter garden. In a greenhouse you can also try fish fertilizer or manure tea, but these are too strong smelling to use in your home.
Plan to feed your baby lettuce with liquid fertilizer after each harvest. When treated this way you can expect three harvests of baby lettuce from each planting, every 3 to 4 weeks. When you are finished harvesting your lettuce, just dump the soil in the compost, then wash and sanitize the container. Now you are ready to replant with fresh soil to start the cycle again.
Since your container can be harvested every 3 to 4 weeks, consider staggering your plantings when growing lettuce indoors. (Kind of like the succession planting you’ll use in your outdoor garden.) If you plant a new container every week, for a month, and give the lettuce what it needs to thrive, you’ll have a continual supply of lettuce over the winter.
Where to get lettuce seed for growing indoors?
Butterhead and loose-leaf lettuce varieties are the best choice to grow in containers. They mature faster than romaine and iceberg types, and make fast growth early on. Look for lettuce varieties that mature in 45 to 55 days. Or buy a mix of lettuce seed specifically chosen for baby leaf production.
You can find seed in the specialty seed catalogs that cater to market gardeners. Many of these catalogs carry fast maturing lettuce with interesting leaf colors and shapes specifically for baby leaf production. In Canada I get my seed at West Coast Seeds (see pages 38 to 40 in their 2016 catalog). In the USA try Annie’s or Baker Creek.
Related: Try Growing Lettuce Hydroponically
How to harvest your baby lettuce
After four weeks your baby greens should be ready to harvest. The leaves will be 3-4″ high. Using scissors, cut them off ½ inch above the soil surface. Wash them well. Drain them or put them through a salad spinner. Use them as you would lettuce or spring greens in a salad or stir fry.
You can grow lettuce indoors!
Don’t hesitate to try growing lettuce at home. Lettuce seed is inexpensive. Soil is cheap. The investment in a grow-light set up will pay for itself over time. And if you live where the sun shines brightly year round, you don’t even need a grow-light to get started.