Many herbs—including oregano, thyme, rosemary, and sage—are best propagated for indoor growing by taking a cutting from an existing outdoor plant. To do it, snip off a 4-inch section, measured back from the tip. Strip off the lower leaves and stick the stem into moist, soilless mix, such as perlite and/or vermiculite. To ensure good humidity, cover with glass or clear plastic, and keep the growing medium-moist.
Transition to indoors
Before the first fall frost (while the weather is still on the mild side), start moving your potted herb plants toward their winter home. Instead of bringing them directly inside, put them in a bright, cool "transitional zone," such as a garage, entryway, or enclosed porch, for a few weeks.
Once they've acclimated, move them to an area with lots of sun (south-facing windows are brightest, followed by east or west views). But protect them from heat and dryness. Most herbs prefer daytime temperatures of about 65°F to 70°F, although they can withstand climbs into the 70s. It's especially important that night temperatures drop at least 10°F—down into the 50s would be better—to simulate outdoor conditions.
With the exception of basil, they'll even do well with occasional dips into the 40s. (So turn that thermostat down when you go to bed.) Place them outside on mild days, and give them regular baths to wash off dust.
Water, light, and temperature
Most herbs like to be well watered but don't like wet feet. That's why good drainage is important. Water when the top of the container feels dry, or learn to judge the moisture in the soil by the weight of the pot. Add sand or vermiculite to the potting soil to ensure good drainage.
Learn to juggle water, light, and temperature. An herb in a clay pot in a south-facing window will need more water than one in a plastic pot in an east- or west-facing window. If the light is low, keep the temperature low.
Choose the soil for your indoor herbs carefully. A good commercial potting soil is fine, or for a deluxe mix, blend one part potting soil with one part compost and one part vermiculite, perlite, or sand (or a mixture of all three).
Resist the temptation to use disease- and pest-prone garden soil. And when you pot up garden-grown plants, remove as much of the garden soil as possible without damaging the roots.
Keep such transplants separate from your other houseplants while you're gradually acclimating them to the indoors. If you see insects on a plant during this "quarantine," leave it outside.
If, despite such defenses, your indoor plants do come under insect attack, help the herbs stay healthy by providing the correct mix of light and temperature, and give them regular baths. A plant weakened by hot, dry indoor conditions is even more susceptible to spider mite, whitefly, or aphid damage than a healthy one.
If you choose to use soap sprays to control these pests, remember that the wet spray must come in contact with the insect to be effective. Spray in the evening (and never in bright sunlight) to prevent rapid drying, and wash off residues the next day (or before eating the leaves). Don't spray very young seedlings with soap!
Hold back on the water and fertilizer through December, but when the days start getting longer in mid-January, feed them with liquid seaweed or compost. Even potted soil gets compacted as you water it, so cultivate it with a little fork, then top-dress it with compost.
February is usually a great month for indoor plants because of all the bright light. By March, they are starting to get buds, and in April, be sure to put them outside on a warm day. Then it won't be long before the herbs—and you—are ready to move back to the garden.