Growing Lettuce and Greens Indoors Through Winter
Pick loose-leaf lettuce, and skip the iceberg
When the days shorten and the outdoor garden is done, a windowsill can still grow salad. Lettuce is one of the most forgiving winter crops indoors, as long as you pick the right kind. The University of Illinois Extension says your best bet is loose-leaf lettuce, which can usually be harvested at about four weeks.
Loose-leaf varieties do not need to form a head, so they suit a small pot and a short winter day. Pick outer leaves as you need them, and the plant keeps growing from the centre. Iceberg, by contrast, needs a long season and plenty of space to form a firm head, which makes it a poor fit for a windowsill.
Choose a loose-leaf mix for different colours and flavours in one pot.
Light is the whole game in winter
Indoors in winter, light matters more than anything else. The University of Illinois Extension puts it plainly: lettuce and herbs usually need between six and eight hours of bright light each day, and southern exposure windows are great. A bright south-facing window is your first choice.
If your windows do not get that kind of light, use supplemental lighting. Illinois Extension suggests two 40-watt cool white fluorescent lights held six to twelve inches above the plants for fourteen to sixteen hours per day. Supplemental lighting is not equivalent to natural light, which is why the lights run longer: for every one hour of natural light, you need around two hours of supplemental lighting. Rotate containers every few days so plants grow evenly.
Containers, soil, and a cool spot
Lettuce has shallow roots and needs drainage. Make sure every container has drainage holes, and use a good-quality potting mix. Do not use topsoil or garden soil in containers.
Water when the top of the mix feels dry, and keep pots away from radiators and heating vents. Room temperatures are best at 70 degrees Fahrenheit (21 degrees Celsius) and below, so avoid placing lettuce near a direct heat source.
For a staggered supply, a set of small pots works well. The 1-Gallon Jute Grow Pots (5-Pack), $33.75 CAD (regularly $40.00) lets you sow one pot this week and another in a fortnight. If sill space is tight, a 3-Pocket Vertical Living Wall Planter, $42.75 CAD (regularly $50.00) turns a bright wall into a small salad garden. Check wall planters often, as they dry out faster than pots on a sill.
Sow little and often, and harvest leaf by leaf
The secret to winter salad is not one big sowing. It is a little, often. Seed company Johnny's Selected Seeds advises sowing every two to three weeks for a continuous supply of full heads or salad mix.
Harvest the same way. Illinois Extension notes that lettuce leaves may be cut when they are large enough to use, and leaf lettuce reaches maximum size in 40 to 60 days. That is the full-size plant, not your first picking: the first baby leaves are ready at about four weeks. Remove the outer leaves when they are three to six inches long and allow the younger leaves to develop. For baby leaf, Johnny's advises harvesting about one inch above the growing point when leaves are three to four inches long.
Start with one pot this week, sow a second in two weeks, and let the rhythm build.
Frequently asked questions
What is the easiest lettuce to grow indoors in winter?
Loose-leaf lettuce. It does not need to form a head, so it suits a windowsill pot, and the University of Illinois Extension notes it can usually be harvested at about four weeks.
How much light does indoor lettuce need in winter?
Six to eight hours of bright light each day, ideally from a south-facing window. If your window does not get that much winter light, run supplemental lights for 14 to 16 hours a day.
How do I harvest lettuce so it keeps growing?
Cut the outer leaves when they are 3 to 6 inches long and let the younger inner leaves keep developing. For baby leaf, cut about 1 inch above the growing point when the leaves are 3 to 4 inches long.
How often should I sow lettuce for a continuous supply?
Sow a small batch every two to three weeks. That succession timing, from seed company Johnny's Selected Seeds, keeps new leaves coming instead of one big harvest all at once.
