Question: I'd like to grow some herbs indoors on the windowsill. Which ones grow best during the winter months?
-Red Lodge, MN
Answer: The list of those herbs that do not do well indoors is short. Sweet basil, lemon verbena, summer savory, and tarragon are all poor choices because they either go dormant or shed their leaves excessively. With these exceptions, most other herbs do very well in a south-facing windowsill. Oregano, thyme, parsley, and sage can all be grown in small pots and trimmed as needed for the kitchen. Equally valuable, though needing more space, are pots of rosemary and sweet bay (Laurus nobilis). In the onion family, windowsill candidates include chives and both onion sets and garlic cloves, which can be started in pots and the emerging foliage clipped when it reaches a couple of inches high. If you have only an east- or west-facing windowsill, try such herbs as peppermint, spearmint, or lemon balm. Provided they are sheared regularly, these, too, make excellent houseplants.
If you are bringing in herbs that have summered outdoors, be sure that you are not importing whiteflies or other insect pests with them. It is safest to discard any such infested specimens; plants that are intended for human consumption cannot be sprayed with the pesticides used on ornamentals. As for the potting medium, indoor herbs grow best in a mixture of two parts potting soil to one part coarse sand or perlite. Setting the pots in trays lined with gravel will keep them from getting wet feet should you overwater. Cool temperatures (60 degrees Fahrenheit), especially at night, will keep herbs at their best. Where sunlight is inadequate, herbs also do well if given 14 to 16 hours of fluorescent light per day.