As outdoor growing season winds down, gardeners often wonder if it’s possible to continue harvesting fresh salad mixes at home. With some simple steps, you can grow lettuce indoors year round.
Start with a decorative flower pot; it doesn’t need to be large, as lettuce roots are shallow. Fill it 3/4 of the way with potting soil and plant seeds thinly. Water the seeds and keep the planting area moist but not soaked.
1. Temperature
Since lettuce is a cool-season vegetable, you’ll need to keep temperatures fairly consistent for the best results. This helps prevent the plant from bolting prematurely, which makes its leaves unpleasantly bitter.
Choose a sunny window or a room that is warm and bright. Keep the area away from drafty heating and air conditioning vents and frequently-opened exterior doors to avoid sudden temperature fluctuations.
Fill your container with a loose, well-draining potting mix. The soil should be moist but not soaked, and the seeds can generally germinate in one to two weeks. Keep an eye on the growing space to ensure that the seeds are not overcrowded, as this can lead to seedling rot and stunted growth. Water your plants as needed to keep the potting mix moist. This could mean daily for small cell trays or once every couple of days for larger lettuce plants. Use tepid water rather than cold water to avoid fungal diseases like damping off.
2. Humidity
Lettuce seeds germinate quickly in potting soil that’s misted with water on a regular basis. This helps the seeds stay moist but not soaked—too much water will drown them and cause rot.
The location of your lettuce growing area is important, too. Choose a spot that gets at least six hours of sunlight each day (preferably a south-facing window). If you’re growing plants in containers on a windowsill or in a hydroponic garden, you may need to use plastic wicking trays or other containers designed to hold water and prevent overflow.
Plants in containers on a windowsill will dry out more quickly than those under grow lights or in a greenhouse, so you’ll need to monitor them closely and add moisture as needed. This is especially true when the weather turns colder or hotter, as sudden changes in humidity can cause the plants to wilt or develop fungus. For best results, keep the humidity level at about 50 to 70 percent.
3. Water
Lettuce plants require plenty of water. Water is essential for nutrient uptake and to prevent water-borne diseases.
To sow lettuce seeds, use a seed starter mix in a plastic container with a slanted bottom that allows water to drain away from the root ball. Mist the potting soil on a daily basis to keep it moistened. Seeds will germinate in 7-14 days depending on the variety.
For mature head-forming lettuce varieties, plant them in a sunny location where they will get at least 12 hours of sunlight a day. A bright light source, such as a window or a specially designed system tabletop grow lights, will help to ensure that the crop gets enough light to develop full heads of crunchy lettuce.
To reduce the risk of disease, sanitize the containers that were previously home to another type of plant before using them for growing lettuce indoors. This will prevent the introduction of fungi, bacteria or viruses that could harm your crops.
4. Light
For a salad bowl-ready harvest, choose loose leaf varieties that don’t form a head and grow quickly. Look for the days to maturity on your seed packet as a guide. Loose-leaf varieties also do well in winter environments, whereas head lettuce can go limp in colder temperatures and may bolt early (develop a flower stalk) under high heat.
Provide adequate spacing to encourage nutrient uptake. Crowded plants compete for airflow, nutrients and root space and can develop spindly growth.
For the best results, follow the recommendations for temperature and light requirements on your specific lettuce variety’s seed packet. If your indoor growing environment doesn’t meet these conditions, consider a simple artificial lighting set-up to help your lettuce thrive. This will reduce the amount of time that your crop needs to be in the garden before it is ready for a salad! Providing adequate light will also reduce the chance of fungal diseases, which can cause diseased or bitter-tasting leaves.