How to Grow Lettuce Indoors
Grow a salad on a sunny windowsill or under full-spectrum grow lights
THERE'S nothing quite like the taste of fresh-picked greens, straight from the garden. For most of us, that's a pleasure reserved for spring through fall. However, salad lovers can grow lettuce indoors, all winter long. Depending upon available sunlight, you can raise a steady supply of your favorite greens on a windowsill or beneath grow lights.
Select the best location. Take a walk through your living space to determine suitable, sunny spots — ideally, a place that gets 12 hours of bright light each day. For lettuce, a south-facing window is best. Even better: a south-facing bay window.
If you have a window that gets 12 hours of bright light each day, you can grow lettuce in the Mobile Grow Cart.
Chris Ahrens, who works in Gardener's Supply's marketing department, grows lettuce in the My Greens Light Garden — right in his cubicle. With five growing trays, it's easy to grow several crops. This tabletop garden has three kinds of lettuce — including a tray of romaine that's almost ready for harvest — wheatgrass, leaf lettuce and calendula, a flowering plant that will be transplanted outdoors in spring.
If you don't have enough light on a windowsill, grow your crop under lights. Specially designed systems, such as the My Greens Light Garden, are perfect for growing small crops of lettuce. Larger light gardens, such as our Vermont-made SunLite® systems, will accommodate even more growing trays.
Your chosen location must also be a safe one. Pick a spot away from active heat sources and cold drafts, and inaccessible to mischievous, hungry pets.
Choose your container, growing medium and seeds. Flat, fairly shallow containers with good drainage are ideal. Other options include 4" to 6" plastic pots or a multi-cell seed-starting system (as shown in our slideshow, above). You can also recycle produce containers or take-out dishes, some of which come with clear covers handy for seed starting. Wash them well and poke a few holes in the bottom for drainage.
For soil, choose a planting mix that's made for seed starting, such as Eco-Co® Coir Seedsarting Mix or Germinating Mix. Do not use garden soil or "potting soil," which is often too coarse for seed starting.
When it comes to choosing seeds, some varieties are better suited to indoor growing. Look for loose-leaf varieties, such as Baby Oakleaf, Tom Thumb and Black-Seeded Simpson. Some varieties are known to grow well in winter light, such as Arctic King, Winter Marvel and Winter Density. You can also try growing other salad bowl favorites, such as spinach, arugula (Astro is a variety that does well indoors) and mesclun. Avoid head lettuces, which are difficult to grow indoors.
Plant and wait. Moisten the soil to prepare it for planting, then fill containers with about 3-4" of prepared mix. Scatter seeds on top of the mix or arrange seeds in rows, trying to keep them about an inch apart. Cover the seeds in a very thin layer of planting mix. If you're using a multi-cell seed starting system, plant three or four seeds in each cell.
Place your containers in a warm location, on a small tray to collect excess water. To maintain moisture, cover them loosely with plastic wrap or a lid. Check daily for signs of sprouts. Once sprouts appear, remove the cover and thin the seedlings so they're about an inch apart. Scissors work well for this task. Keep the seedlings moist but not overwatered.
You can harvest the crop all at once or do it gradually. Start with the outer leaves first and leave the rest to grow a few days longer.
Monitor growth and make adjustments. Lettuces are delicate and require extra attention when grown indoors. Your seedlings should look green and robust; leggy, yellowed plants are light-starved. Once your tiny plants have their first set of true leaves, start feeding them with a liquid fertilizer, such as Easy Grow Fertilizer. Monitor the moisture level to make sure your seedlings are moist but not waterlogged. A seed-starting system with a wicking mat and a water reservoir makes it easy to keep your lettuce watered.
Harvest! In about three to four weeks, indoor baby lettuce should be around 4" inches tall and ready to harvest. Because lettuce is perishable, cut only what you need. Starting with the outer leaves first, trim each leaf at the plant's base, about an inch from the soil. Leave the remaining leaves to grow for a few days longer. When the harvest is complete, plant another set of seeds.