With enough light and heat, you can grow your own vegetables all year round.
Just because the days are getting cooler and shorter here in the northern hemisphere, that doesn't mean you should stop harvesting homegrown food. Instead, consider starting an indoor garden with edible crops that you can enjoy throughout the winter. According to The Gateway Gardener, it's not that hard, and actually sounds rather fun.
Generally speaking, plants that are harvested for their leaves tend to do much better indoors than ones whose fruit is eaten. For example, microgreens, sprouts, and lettuces are easier to grow than tomatoes, peppers, and cucumbers.You'll need pots of sufficient size with adequate drainage. A four-inch diameter is enough for lettuce and herbs, whereas cherry tomatoes would need a 1-2 gallon pot, and anything larger at least 5 gallons.
Start plants from seeds or buy some starter herb plants at a greenhouse or supermarket. Robert Weaver, editor at The Gateway Gardener, suggests:
"Fill the containers with a soilless starting mix, moisten, plant the seeds at the depth recommended on the seed packet, cover the soil with plastic to keep it from drying out, and place in a warm window or even on top of the refrigerator. They don’t need light to germinate. After they start to germinate, remove the plastic, and place in a sunny location or under grow lights. Once seedlings reach a couple inches and have 2-3 sets of true leaves, transplant them in their own containers."
Greater care must be taken to keep indoor plants well-lit. If you can, place them in a south-facing window that gets plenty of sunshine and natural light. The reason leafy plants do better than fruiting plants is because the latter requires more light to produce flowers and fruit, but this is achievable with artificial light. Weaver writes:
"When comparing lights, you need to consider their output in two terms — color and intensity. Plants respond in certain ways to certain color spectrums. Of course daylight has it all, but artificial lighting sometimes only provides a limited spectrum, and varying degree of intensity. Once again, leafy veggies and herbs will do fine with less intense lighting, while anything larger than 12” will require a little more 'oomph!' For the cooler lights (fluorescents and LED) keep the light source about 4″ above the top of the plant. Others will have to be at a greater distance away to prevent frying the plants."
He compares fluorescents, High Intensity Discharge lights, and LEDs. You can read a more detailed comparison here.
Plants must be watered diligently because indoor air gets very dry in wintertime. Check the soil and, if it feels dry to the touch, add some water.
If you're growing tomatoes or peppers, you will have to aid with pollination, since there are (hopefully) no bees buzzing around your house. Peppers dislodge their pollen easily, so you can do this by dabbing the flowers with a cotton swab and transferring to other flowers. With tomatoes, use an electric toothbrush simply to jiggle the flower and release pollen to encourage self-pollination.
Which crops should you start with? Modern Farmer has a good list, some of which I've shared below:
Herbs: Mint is the most shade-tolerant, whereas basil and dill need a room that does not drop below 60F (15.5C) at night.
Greens: Lettuce, arugula, kale, and spinach grow well indoors, but are best harvested as baby greens, before reaching maturity. Brian Barth writes for Modern Farmer, "Greens do not need supplemental light if located in a sunny, south-facing window. Otherwise, provide 10 to 12 hours of artificial light daily."
Cherry tomatoes: These grow more readily than full-size tomatoes, although they need 16 hours of artificial light daily and temperatures that do not go below 65F (18C). Chili peppers do well under these same conditions.
Sprouts & Microgreens: Pick up a sprouting kit for an easy way to add fresh crunch to your salads and sandwiches; the seeds germinate and grow quickly and do not require direct sunlight. Microgreens are sprouts grown in soil that have been allowed to grow a bit longer, to develop small leaves. Barth advises,
"Harvest once the first leaves emerge by cutting them with scissors just above the soil. Greens of all types are ideal for harvesting as microgreens, as are peas (that’s how you get pea shoots), and root crops, like turnips, beets, and radishes."