Just because days are shorter and colder and the outdoor gardening days are over, doesn't mean that it all must come to an end. Indoors we can have our green houseplants, but what if I told you – you can have herbs and lettuce and eat them too!
You can grow a number of herbs and lettuce indoors even in the middle of winter, short days and all. Whether you are growing indoors or outdoors, please still have the same needs but indoors in winter the two restricting factors that can affect growth is light levels and humidity.
Lettuce and herbs usually need between 6-8 hours of bright light each day. Southern exposure windows are great. If your windows don't receive that kind of light during the winter months, you can use supplemental lighting. You can use specialty grow lights, which can be more expensive, or you can use 2 40 watt cool white fluorescent lights held 6-12 inches above the plants for 14-16 hours per day. Supplemental lighting is not equivalent to natural light which is why the lights need to run for longer. For every 1 hour of natural light you need around 2 hours of supplemental lighting. Room temperatures are best 70 degrees and below so make sure to avoid placing your herbs or lettuce near a direct heat source.
If you are lucky enough to have a window with lots of natural light make sure to rotate your containers every few days. Plants will lean towards the light which is called phototropism. So to encourage even growth turning the containers is helpful and recommended.
Make sure all the containers you are using to growing your herbs or lettuce have drainage holes and utilize a good quality potting mix. Don't use top soil in your containers. You'll want to plan on a water-soluble fertilizer every 2 weeks for your herbs, but don't fertilize more often. Fertilizing more often can negatively affect the flavor and aroma of your herbs.
To increase humidity you can cluster plants together making sure to give some space between for good air circulation. Another option is a tray with pebbles in it. Fill the tray with water to just below the tops of the pebbles and place your pots on the top of the pebbles. As the water evaporates it adds extra humidity to the air.
At this point you're probably wondering what herbs you can grow indoors and what kind of lettuce. With lettuce, your best bet is loose leaf lettuce. Usually loose leaf lettuce can be harvested at about 4 weeks. I'm a fan of loose leaf lettuce mixes and they are great in the garden in spring and fall as well. As for herbs – basil, chives, oregano, thyme, winter savory, rosemary, parsley, sage and mint all do well indoors. For herbs – harvest what you need when you need it for use in cooking. If you are using fresh herbs in place of dried herbs in recipe the conversion rate is 1 tablespoon of fresh herbs for every 1 teaspoon of dried.