Not every herb likes indoor life. Coriander (cilantro), garden cress, and dill are short-lived annuals that, when cut for harvest, do not regrow. You have to resow these herbs to produce a continuous crop. Three pots of each plant, each at a different stage (seeded, intermediate growth, and ready to cut), are usually enough. Forget trying to grow coriander, dill, or other spice herbs indoors for their seeds: They won't set enough to warrant the effort.
You can grow parsley in pots, but I prefer to bring in established plants from the garden at the end of the season. The older leaves will fall off, but the thick taproot will drive new growth from the center. However, parsley grown indoors from seed never reaches the size and productivity of plants dug from the garden. That's why I dig outdoor plants in fall and bring them inside. Keep the soil around the taproot intact, and be sure to use a pot that's deep enough to accommodate the root.
Unless light is plentiful, growth of most indoor herbs will slow or even stop during the winter, even with enough warmth. When growth slows, reduce harvests and hold back a little on the water. Reducing the indoor temperature to 60° to 65°F, if possible, also helps.
French tarragon and chives in particular benefit from a cool period. When growth flags in winter, place them in an unheated shed or garage (or in the refrigerator) for a month or two; freezing temperatures are fine. When returned to room temperature and good light, they'll put out succulent new growth.
My mother, co-founder of Richters Herbs, grows herbs indoors in window boxes. She "plants" herbs in their pots in a window box filled with soil up to the rim of the pots. This system may seem odd, because the roots can only get at the soil outside through the holes in the pots. But herbs do precisely that, with faster and more lush growth than in stand-alone pots. The extra soil prevents the plants from becoming potbound, humidity and soil moisture remain more even, and the herbs seem to grow better. Also, the roots don't become so intertwined that it's difficult to rearrange or replace plants. A firm yank dislodges them.
Herbs are sun worshipers for the most part. As expatriates of the Mediterranean region, most flavorful herbs don't thrive in the un-Mediterranean environment and inadequate light our houses provide. Herbs don't tolerate north-facing windows, or any window that gets less than four hours of direct sunshine a day.
Provide light. Even if your indoor herbs get their four hours of direct sunshine daily, installing supplementary lighting is a necessity. The light coming through a window may seem bright to your eyes, but its intensity in winter is often less than one-tenth of the outdoor light during a summer day. Grow lights will work if their light intensity is high enough and the spectral quality is right.
Acclimate plants gradually. Plants produce two kinds of leaves in response to strong or weak light. High-light leaves are thick, strong, and narrow. Low-light leaves are thinner, more delicate, and broader than high-light leaves. But narrow high-light leaves are less efficient in converting light energy into food than low-light leaves. High-light leaves are accustomed to an abundance of light, so they don't have be as efficient at food production. A plant that is adapted to abundant light often turns brown and drops leaves indoors. This is because it can't produce enough food to maintain itself. The plant tries to make food by shedding the inefficient leaves and producing efficient leaves higher up and closer to the light source. When you bring herbs indoors, this leaf drop and increased leggy growth can happen within weeks, or even days. Some herbs cannot make the transition fast enough to survive.
Rosemary is a case in point. This slow-growing evergreen doesn't have the chance to adjust to changes in light before the plant slowly starves itself. By January, February, or March, the leaves dry up, and the plant dies. This sudden death is by far the most common complaint about growing rosemary indoors. Here's what to do: Gradually adjust the plant to lower light. Place it in partial shade for two to three weeks, then in deeper shade for another two to three weeks before bringing it indoors. When plenty of new growth appears, the plant is ready to go into the house.
Soil, fertilizer, and water. After light, proper soil is the next most important factor in producing healthy herbs. With few exceptions, herbs require excellent drainage, especially during the winter months, when transpiration rates are lowest (that's the rate at which plants release water from their leaves to the atmosphere). When roots are confined in a pot or planter, water and air cannot move easily. To improve drainage without sacrificing nutrients, add sharp sand or perlite to a good sterilized compost-based mix. Most herbs do well in soils of pH 6 to 7.
Many people incorrectly think that herbs grow better in poor soil. Flavors are stronger when culinary herbs grow outdoors in gardens. But in the confines of a pot, supplementary feedings with liquid fertilizer or organic fish emulsion are necessary. Feed herbs once a week when plants are actively growing, but not when dormant.
Watering is not a trivial matter with herbs. In general, water less often and more thoroughly, and only when the soil is actually dry. When the soil is dry to the touch, add water until it comes out the bottom of the pot. If the water doesn't come out, pots have a drainage problem. First, check that the holes aren't blocked; if not, you may have to repot with soil that has better drainage.
Pests and diseases. Herbs are susceptible to common pests, including whiteflies, spider mites, aphids, mealybugs, scale insects, and thrips. Inspect herbs regularly.
If your herbs are in portable containers, control pests by dipping the whole aboveground part of the plant into a pail of insecticidal soap. Swish vigorously for a minute or two to wet all leaf surfaces (hold your hand over the pot to prevent soil loss). Dipping herbs once or twice a week for three to four weeks will clear up most problems.
Over the years, many new varieties of herbs have been introduced, some of which do better indoors than the traditional varieties. Here are 10 herbs notable for their consistent, compact growth habit and strong flavor.
'Grolau' chives (Allium schoenoprasum): Strong flavor and thick, dark green leaves. Developed for forcing, 8 to 12 inches tall. Seeds germinate in 10 to 14 days at 60° to 68°F.
'Fernleaf' dill (Anethum graveolens): Dwarf form of dill only 18 inches tall. Ideal for dill weed indoors. Standard varieties grow too tall and bolt too soon. Easy from seeds, germinating in 7 to 14 days at 60° to 68°F.
'English' mint (Mentha spicata): Perhaps the best-behaved spearmint variety (not as invasive as others, and the leaves are broader and deeper green). Excellent for cooking and tea. Easy to propagate from cuttings.
'Spicy Globe' basil (Ocimum basilicum minimum): Dense, compact form of basil, 8 to 10 inches tall. Good flavor. Grow from seed; germinates in 6 to 12 days at 68° to 77°F.
Greek oregano (Origanum vulgare hirtum): The true oregano for Mediterranean cooking, with excellent flavor and white flowers. Watch out for the impostor (called wild marjoram) with pink flowers and no flavor. Greek oregano grows well in pots, reaching 8 to 12 inches. Grows easily from seed in 7 to 21 days at 65° to 72°F.
Broadleaf thyme (Plectranthus amboinicus or Coleus amboinicus): Also known as Spanish thyme and Cuban oregano, this plant has broad, fleshy leaves unlike those of ordinary thyme. Wonderful, spicy thyme-oregano flavor and useful in many of the same recipes as ordinary thyme. Never goes dormant. Grows from cuttings only, and reaches 10 to 12 inches tall.
Vietnamese coriander (Polygonum odoratum): Not true coriander, but a good substitute. Regrows after cutting, unlike true coriander, which must be reseeded after harvest. Grows 4 to 8 inches tall. Propagate from cuttings.
'Blue Boy' rosemary (Rosmarinus officinalis): More compact and diminutive than regular rosemary, reaching only 24 inches. Flowers freely and has excellent flavor. Propagated by cuttings only.
Dwarf garden sage (Salvia officinalis 'Compacta'): Smaller leaves and more compact habit than regular sage, growing only 10 inches high. Same sage flavor. Propagated by cuttings only; seeds are unavailable.
Creeping savory (Satureja repandra or S. spicigera): Flavor identical to that of winter savory, but easier and faster to grow indoors. Reaches only 2 to 4 inches in height, but fills the pot with a dense mat of foliage. Difficult to find seeds, but grows readily from cuttings.
So consider growing herbs indoors at home or in a school garden. Photograph by Suzanne DeJohn/National Gardening Association