Yes, You Can Have Homegrown Lettuce All Year
By Wendy MacLean, Master Gardener
A trio of reasons motivate me to grow lettuce (Lactuca sativa) indoors: the carbon footprint of transporting lettuce long distances to my home; the shocking price of one head of lettuce at grocery stores in the winter; and the memory of a family member being sickened by E. coli a few years earlier, at the same time health authorities had issued warnings about imported lettuce.
What influenced me to sow the lettuce seeds when I did was my craving for “greens,” which begins in February during our long Prairie winter. Since many seed packages state that the “baby leaf” stage is reached about 30 days from sowing and “full size” at 45–60 days, I chose the dates of December 13 and 14 to sow my seeds. In this way, I calculated that I could begin eating fresh, home-grown salads by early to mid-February.
What you need
Growing lettuce indoors requires consideration of the containers, growing medium, seeds, and plant care needed to ensure success.
Containers. I retrieved four clean rectangular planters, 61 cm or 81 cm long by 20 cm wide by 15 cm deep (24 in. or 32 in. long x 8 in. wide x 6 in. deep), and a few smaller plastic containers saved from a store-bought BBQ chicken. A depth of 15 cm (6 in.) is adequate for lettuce’s shallow root system. Ensure that all containers have good drainage holes, to avoid soil waterlogging and root rot. Place the containers on trays to catch any excess water. If you plan on harvesting just a few leaves every couple of days, grow one to three plants in a 20‑cm (8‑in.) pot.
Soil. I used a good-quality potting mix for the initial sowing of seeds in smaller containers. For the direct-sown ‘Ovations Mix’ and for transplanting the lettuce seedlings into the larger planters, I used about two parts of this potting mix moistened to the damp sponge stage and one part of moist, good-quality compost gently mixed into the top 5 – 7.5 cm (2 – 3 in.) of the growing medium. This compost helps retain moisture and adds nitrogen. (Leafy greens grow quickly and need sufficient nitrogen.) If the growing medium has no fertilizer, feed them a balanced fertilizer every two weeks or so after true leaves appear. Try a balanced 10-10-10 or 5-5-5 water-soluble or granular fertilizer, diluted to half strength. I, however, found that the addition of compost provided sufficient nutrients.
Seeds. My stack of partly used seed packages from the previous summer provided ‘Black Seeded Simpson’, a loose-leaf lettuce (Lactuca sativa), and ‘Buttercrunch’, a butterhead type (Lactuca sativa var.capitata1). To give my salads variety, I also chose ‘Ovations Mix’ (Brassica spp.), which is a combination of red mustard (Brassica juncea), mizuna (Brassica rapa), tatsoi (Brassica rapa), kale (Brassica oleraceae),and arugula (Eruca sativa).
I initially sowed the seeds into the smaller containers for later transplanting at the true-leaf stage into larger planters, to ensure that no blank spaces were left where seeds did not germinate. This also helped me space the plants with adequate distance between them, as it is very easy to sow the small seeds too closely together. Since the seed package for the ‘Ovations Mix’ stated that these do not transplant well, I sowed these directly into one larger planter.
Photo: Wendy MacLean – Young lettuce seedlings in first container
Lettuce seeds need lots of light for optimal germination. You can lightly cover them with moist soil or simply press the seeds into the top of the soil. Cover the various small Brassica seeds in the ‘Ovations Mix’ lightly too. A good guide is a depth of 0.5 cm (0.25 in.).
To eat lettuce earlier, choose varieties with the fewest days to maturity and those you can harvest early as “baby leaf.” Varieties that can be eaten at the baby leaf stage include ‘Deer Tongue’, ‘Black Seeded Simpson’, ‘Red Sails’, ‘Lollo Rossa’, and ‘Rouge d’Hiver’. To have an ongoing supply of fresh greens, sow seeds every 2–4 weeks.
Finally, bear in mind that most lettuce and Brassica seeds retain viability for five years if stored in a cool, dark, and dry place.
Photo: Wendy MacLean – Lettuce with first set of true leaves
Transplanting. By January 2, my seedlings had developed their first set of “true leaves,” and I transplanted them into the larger planters. To make the best use of space, I staggered the plants in two rows along the length of the planters. At this stage, too, ensure that the growing medium is moist for the tiny roots of the seedlings. When transplanting young seedlings, handle them by their leaves and not by their stems, which can be easily crushed.
Growing conditions. I placed the containers and planters on shelves with grow lights about 15 cm (6 in.) above them. I used two 60-cm (24-in.) full-spectrum T5HO 24W 6400oK lights, two per shelf; this allowed for one light per planter. To begin, I kept the lights on for 16 hours and off for 8 hours; once they germinated and started growing, I gradually cut back the time to 8 hours on and 16 hours off, as lettuce grows well in part sun and I wanted to reduce energy use. (Also, bolting occurs when daylight hours lengthen and temperatures increase, and I hoped to delay this.) The plants continued to grow well, even with fewer hours of light. I set up this grow-op in our basement where the temperature was between 17o C and 18o C (62–64o F). By January 21, the lettuce seedlings had grown significantly.
Keep the soil consistently moist, as lettuce is 90–99% water.2 Less-frequent watering is needed indoors than outdoors, as the plants are not exposed to hot, drying winds. You may need to water more often than once per week when the plants are larger, because at that point they will have more leaf surface area and therefore transpire more. When watering, add water until it seeps out from the bottom drainage holes and onto the trays; at this point you will know that water has reached the roots where it is needed. As the plants grow, raise the lights so that they are 2.5 to 5 cm (1–2 in.) above the tender leaves. If the leaves come into contact with the lights, they can become scorched. Note that lettuce prefers cooler temperatures, ideally below 21o C (70o F).
Photo: Wendy MacLean – Ovations Mix
Harvesting. I started harvesting leaves from the ‘Ovations Mix’ on January 17; by January 22, I could cut some baby lettuce leaves. By January 31, many leaves were big enough to use in sandwiches and salads. There are two main ways to harvest salad greens. One is to harvest the mature outer leaves first and let the inner leaves continue to grow to mature size. The other method is called “cut and come again”: when the plants are 15 cm (6 in.) high, cut all the leaves down to about 4 cm (1.5 in.) high. The plants will grow and give you another harvest or two. By mid-February, there were many full-sized leaves and salads became a regular menu item in our house.
Observations. The ‘Ovations Mix’ grew to maturity two weeks sooner than the lettuce. This may be due, in part, to the fact that they had not been set back by transplanting. These greens are ready to harvest at a “baby leaf” stage. The ‘Ovations Mix’ easily gave three harvests of sturdy leaves.
Lettuce leaves that are grown indoors are delicate because they are not exposed to outdoor elements; be sure to handle them gently.
Photo: Wendy MacLean – Using the first leaves in vegetarian wrap
Advantages of indoor growing. In addition to reducing my carbon footprint, food cost, and the risks to food safety, I discovered other reasons that made this endeavour worthwhile. I liked being able to take two or three leaves for a sandwich and let the rest continue to grow; fresh greens were available for at least two months. My indoor lettuce did not suffer damage from slugs, flea beetles, or cabbage butterfly caterpillars, all of which had been known to attack Brassica crops in my outdoor garden; it was also safe from rabbits. The leaves were very clean, needing only a quick rinse before use. And importantly, salads made from these freshly harvested greens tasted delicious. The “feel good factor” from seeing something green growing in the coldest, darkest days of winter and the sense of self-sufficiency were bonuses.
Photo: Wendy MacLean – ‘Buttercrunch’ and ‘Black Seeded Simpson’
Future growing plans. To add more colour to future salads, I plan to include a red leaf variety such as ‘Lolla Rossa’ or ‘Red Oak Leaf’; I would also like to grow some baby spinach and beet leaves. There are smaller varieties of cucumbers and tomatoes that can be grown in containers. The possibilities continue to expand as new cultivars arrive on the scene, and I can envision even more beautiful and interesting indoor-grown salads in my future.
1 Butterhead lettuce types are distinguished from regular head lettuce types, in that the former feature loose heads and can be harvested as individual leaves.
2 For information on various foods and their water content see www.ncbi.nlm.nih.gov/pmc/articles/PMC2908954/table/T1/.
*This article originally appeared in The Prairie Garden and has been reprinted with permission.*