Year-Round Indoor Herb Garden: Light, Water, and Fertilizer for 15 Culinary Herbs

Light Requirements and Fixture Selection

Indoor herbs fall into three light categories: high-light herbs that require 12 to 16 hours of intense light, moderate-light herbs that thrive on 10 to 12 hours, and low-light herbs that survive on 8 to 10 hours. No indoor location provides enough light for high-light herbs without supplemental lighting, and even moderate-light herbs perform poorly on windowsills from November through February in most of North America.

LED vs. Fluorescent

T5 fluorescent (2 to 4 tubes, 24 to 48 inches): Produces 2,000 to 5,000 lumens. A 4-tube, 48-inch T5 fixture draws 216 watts and produces 20,000 lumens. Costs $40 to $60. Fixture lifespan: 20,000 to 30,000 hours (2 to 3 years of daily use at 12 hours per day). Tube replacement: $8 to $12 per tube every 2 years. LED strip or panel (full spectrum, 3000 to 5000K): Produces 2,000 to 8,000 lumens depending on wattage. A 45-watt LED panel (12 by 12 inches) produces 3,000 lumens and covers a 2-by-2-foot area. Costs $25 to $40. Lifespan: 30,000 to 50,000 hours (5 to 8 years). No tube replacement required. LEDs use 40 to 50 percent less electricity than T5 fluorescents for equivalent light output and produce less heat, which allows the fixture to be positioned closer to the plants (6 to 12 inches versus 2 to 4 inches for fluorescents). For a kitchen herb garden of 10 to 15 plants in 4-inch pots, a single 45-watt LED panel on a timer is the most cost-effective option.

Fixture Placement

Position the light source 6 to 12 inches above the tops of the herbs. Light intensity decreases by the inverse square of the distance: doubling the distance from the light reduces intensity to 25 percent. If herbs stretch toward the light, develop long internodes (spaces between leaves), or produce pale, thin leaves, the light is too far away. Raise the fixture as plants grow, maintaining the 6 to 12-inch gap. Use a simple outlet timer ($6 to $10) set to 12 hours on, 12 hours off. Herbs need a dark period for respiration; continuous 24-hour lighting reduces growth and flavor quality in basil, cilantro, and dill by 15 to 20 percent.

High-Light Herbs (12 to 16 Hours of Light)

These Mediterranean herbs originate in sunny, well-drained environments and demand the most light and the dridest soil of any culinary herbs. They are the most challenging to grow indoors without supplemental lighting but reward the effort with intense flavor.

Basil (Ocimum basilicum)

Light: 14 to 16 hours. Minimum 200 micromoles per square meter per second (umol/m2/s) PPFD. Water: When the top 1 inch of soil is dry. Typically every 2 to 3 days in a 6-inch pot. Basil wilts visibly when underwatered but recovers within 2 to 3 hours of watering. Fertilizer: 1/2 teaspoon of 10-10-10 water-soluble fertilizer per gallon of water, applied every 2 weeks. Basil is a heavy nitrogen feeder; pale yellow lower leaves indicate nitrogen deficiency. Container: Minimum 6 inches in diameter and 6 inches deep. One plant per 6-inch pot. Varieties for indoors: Genovese (classic pesto basil, large leaves, 18 to 24 inches tall), Spicy Globe (compact, 8 to 10 inches, suited for small pots), and Thai basil (licorice-clove flavor, 12 to 18 inches). Harvest: Begin harvesting when the plant has 6 to 8 sets of leaves. Cut the stem just above a leaf pair. Two new branches will grow from the leaf axils below the cut. Harvest up to one-third of the plant's foliage at one time. Never harvest more than two-thirds, which stunts regrowth. A well-maintained indoor basil plant produces 2 to 4 cups of packed leaves per month from April through October.

Rosemary (Salvia rosmarinus)

Light: 12 to 14 hours. Water: When the top 2 inches of soil are dry. Typically every 5 to 7 days in a 6-inch pot. Rosemary is the most drought-tolerant culinary herb. Overwatering kills rosemary faster than underwatering. Yellowing needles and a soggy, dark root zone indicate root rot (Phytophthora spp.), which is fatal. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, applied every 4 weeks. Rosemary requires less fertilizer than most herbs. Excess fertilizer produces soft, sappy growth with reduced essential oil content. Container: 6 to 8 inches in diameter and 8 inches deep. Terracotta pots are preferred over plastic because the porous clay allows faster soil drying. Varieties: Tuscan Blue (upright, 24 to 36 inches, best flavor), Prostrate (trailing, 12 to 18 inches, suited for hanging baskets), and Arp (cold-hardy, survives to 15 degrees Fahrenheit outdoors). Lifespan: Rosemary is a woody perennial that lives 10 to 15 years indoors with proper care. Purchase a small nursery plant ($4 to $6) rather than starting from seed; rosemary seeds germinate at only 30 to 40 percent and take 21 to 28 days to sprout.

Thyme (Thymus vulgaris)

Light: 12 to 14 hours. Water: When the top 1.5 inches of soil are dry. Typically every 4 to 6 days in a 4-inch pot. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 4 weeks. Container: 4 to 6 inches in diameter. Thyme has a shallow root system and thrives in small pots. Varieties: Common thyme (Thymus vulgaris, classic culinary thyme, 6 to 12 inches), Lemon thyme (Thymus x citriodorus, citrus flavor, 4 to 8 inches), and Creeping thyme (Thymus serpyllum, ornamental ground cover, edible but less flavorful). Harvest: Cut stems 2 to 3 inches above the soil. Thyme is woody at the base; do not cut into the woody portion, which does not regrow. A 6-inch thyme plant produces 1/4 to 1/2 cup of stripped leaves per month.

Oregano (Origanum vulgare)

Light: 12 to 14 hours. Water: When the top 1.5 inches of soil are dry. Every 4 to 5 days in a 6-inch pot. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 3 to 4 weeks. Container: 6 inches in diameter. Varieties: Greek oregano (Origanum vulgare subsp. hirtum, the standard for Italian and Greek cooking, 12 to 18 inches, the most pungent variety), Italian oregano (O. x majoricum, milder, 12 to 18 inches), and Golden oregano (ornamental, mild flavor, 6 to 8 inches). Harvest: Cut stems back by one-third every 4 to 6 weeks to promote bushy regrowth. Oregano flavor intensifies as leaves dry; fresh oregano is milder than dried.

Moderate-Light Herbs (10 to 12 Hours of Light)

These herbs tolerate slightly lower light levels and moister soil than the Mediterranean group. They are the easiest category for beginners and perform adequately on a bright windowsill from March through October, though they still benefit from supplemental light in winter.

Parsley (Petroselinum crispum)

Light: 10 to 12 hours. Water: When the top inch of soil is dry. Every 2 to 3 days in a 6-inch pot. Parsley has a deep taproot and tolerates slightly drier conditions than basil or cilantro. Fertilizer: 1/2 teaspoon of 10-10-10 per gallon, every 2 weeks. Parsley is a heavy feeder; yellowing lower leaves indicate nitrogen deficiency. Container: 6 to 8 inches deep to accommodate the taproot. Varieties: Italian flat-leaf (P. crispum var. neapolitanum, preferred for cooking, stronger flavor, 12 to 18 inches) and Curly-leaf (P. crispum var. crispum, garnish, milder, 10 to 14 inches). Growth: Parsley is a biennial. In its first year, it produces a rosette of leaves. In its second year, it sends up a flower stalk and dies. For continuous harvest, start new plants every 6 months. Seeds germinate slowly (21 to 28 days) and benefit from soaking in warm water for 24 hours before sowing. Harvest: Cut outer stems at the base. The center of the plant continues producing new growth. A 6-inch parsley plant yields 1/2 to 1 cup of chopped leaves per month.

Cilantro (Coriandrum sativum)

Light: 10 to 12 hours. Cilantro bolts (goes to seed) rapidly when temperatures exceed 75 degrees Fahrenheit or when day length exceeds 12 hours. Indoor growing in a cool room (60 to 70 degrees) with 10 to 11 hours of light extends the harvest window to 6 to 8 weeks per planting. Water: Keep soil consistently moist but not saturated. Water when the top 0.5 inch of soil feels dry. Every 1 to 2 days in a 4-inch pot. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 3 weeks. Container: 4 to 6 inches in diameter. Varieties: Santo (slow-bolting, 12 to 18 inches, the standard variety for indoor growing), Calypso (slowest bolting, 10 to 14 inches), and Confetti (fine, feathery leaves, milder flavor, 10 to 12 inches). Succession planting: Sow new seeds every 3 to 4 weeks for continuous harvest. Each planting produces for 6 to 8 weeks before bolting. Keep 3 to 4 pots at different growth stages for a steady supply. Harvest: Cut entire stems at soil level when the plant is 4 to 6 inches tall. The plant regrows once or twice before bolting.

Mint (Mentha spp.)

Light: 10 to 12 hours. Mint tolerates lower light than most herbs and grows in a north-facing window, though growth is slower and stems are longer. Water: Keep soil consistently moist. Mint wilts rapidly when dry and recovers slowly. Water when the top 0.5 inch of soil is dry, typically every 1 to 2 days in a 6-inch pot. Fertilizer: 1/2 teaspoon of 10-10-10 per gallon, every 2 weeks. Mint is an aggressive feeder. Container: Minimum 6 inches in diameter. Always grow mint in its own pot; it spreads by runners and will overrun any container it shares with other herbs. Varieties: Spearmint (Mentha spicata, the standard for mojitos and tabbouleh, 12 to 24 inches), Peppermint (M. x piperita, menthol flavor, 12 to 18 inches), Chocolate mint (M. x piperita f. citrata, chocolate-mint flavor, 12 to 18 inches), and Apple mint (M. suaveolens, mild, fruity, 18 to 24 inches). Harvest: Cut stems back by one-third every 2 to 3 weeks to prevent legginess. A 6-inch mint plant produces 1 to 2 cups of leaves per month.

Chives (Allium schoenoprasum)

Light: 10 to 12 hours. Water: When the top inch of soil is dry. Every 3 to 4 days in a 4-inch pot. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 3 weeks. Container: 4 to 6 inches in diameter. Chives are clump-forming and multiply by bulb division. Divide the clump every 2 to 3 years. Varieties: Common chives (A. schoenoprasum, onion flavor, 12 to 18 inches) and Garlic chives (A. tuberosum, garlic flavor, white flowers, 12 to 18 inches). Harvest: Cut individual leaves 1 inch above the soil with scissors. The plant regrows from the base. Harvest up to one-third of the leaves at one time. Chives are perennial and produce for years indoors with minimal care.

Dill (Anethum graveolens)

Light: 12 to 14 hours. Dill has a deep taproot and does not transplant well. Sow seeds directly in the final container. Water: When the top inch of soil is dry. Every 3 to 4 days in a 6-inch pot. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 3 weeks. Container: 6 to 8 inches deep for the taproot. Varieties: Bouquet (standard, 24 to 36 inches, good for both leaves and seeds), Fernleaf (dwarf, 12 to 18 inches, suited for indoor containers), and Dukat (high essential oil content, 18 to 24 inches). Harvest: Begin cutting fronds when the plant is 8 to 12 inches tall. Dill bolts quickly indoors; each planting produces for 4 to 6 weeks. Sow new seeds every 3 weeks for continuous harvest.

Low-Light Herbs (8 to 10 Hours of Light)

These herbs tolerate the lowest light levels and the moistest soil. They are the best candidates for windowsill-only growing, particularly in rooms with east- or west-facing windows that receive 4 to 6 hours of direct sun.

Lemon Balm (Melissa officinalis)

Light: 8 to 10 hours. Water: When the top inch of soil is dry. Every 2 to 3 days. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 4 weeks. Container: 6 inches in diameter. Growth: Lemon balm is a perennial in the mint family that spreads aggressively. Grow in its own pot. Pinch stems regularly to maintain a compact shape. Harvest: Cut stems back by one-third every 4 weeks. The leaves are used fresh for tea (steep 2 tablespoons of fresh leaves in 8 ounces of hot water for 5 minutes) and in salads. Dried lemon balm retains 50 to 60 percent of its essential oil content.

Chervil (Anthriscus cerefolium)

Light: 8 to 10 hours. Chervil prefers cool conditions (60 to 70 degrees) and bolts at temperatures above 75 degrees. It is the ideal indoor herb for cool rooms. Water: Keep soil consistently moist. Every 1 to 2 days. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 3 weeks. Container: 4 to 6 inches. Flavor: Delicate anise-parsley flavor. Used in French cuisine (bearnaise sauce, fines herbes blend). Harvest: Cut outer stems at soil level when the plant is 4 to 6 inches tall. Each planting produces for 6 to 8 weeks. Sow seeds every 4 weeks for continuous supply. Chervil is one of the few herbs that actually prefers indoor conditions to outdoor summer heat.

Sorrel (Rumex acetosa)

Light: 8 to 10 hours. Water: When the top inch of soil is dry. Every 2 to 3 days. Fertilizer: 1/2 teaspoon of 10-10-10 per gallon, every 3 weeks. Container: 6 to 8 inches. Growth: Perennial, produces for 2 to 3 years before needing replacement. Flavor: Sharp, lemony acidity. Used in soups, sauces, and salads. A few leaves chopped into a salad replace lemon juice. Harvest: Pick outer leaves when they are 3 to 4 inches long. The plant regrows from the center. Harvest up to one-third of the leaves at one time.

Five More Herbs Worth Growing Indoors

These five herbs have specific quirks that make them slightly more demanding but worth the effort for their culinary value.

Sage (Salvia officinalis)

Light: 12 to 14 hours. Water: When the top 2 inches of soil are dry. Every 5 to 7 days. Sage is extremely drought-tolerant and prone to root rot in wet soil. Use a terracotta pot and a sandy potting mix (50 percent standard potting mix, 50 percent perlite or coarse sand). Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 6 weeks. Container: 6 to 8 inches. Varieties: Common sage (gray-green leaves, standard culinary variety, 18 to 24 inches), Berggarten (compact, broad leaves, 12 to 18 inches, excellent for containers), and Tricolor (variegated pink, white, and green leaves, 12 to 18 inches, milder flavor). Harvest: Cut individual leaves or stem tips. Do not harvest more than one-third of the plant at once. Sage flavor is strongest just before the plant flowers.

Tarragon (Artemisia dracunculus)

Light: 12 to 14 hours. Water: When the top 1.5 inches of soil are dry. Every 4 to 5 days. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 4 weeks. Container: 6 to 8 inches. Varieties: French tarragon (A. dracunculus var. sativa, the only culinary tarragon, cannot be grown from seed, purchase nursery plants, 18 to 24 inches) and Russian tarragon (A. dracunculoides, inferior flavor, grows from seed, avoid). Important: French tarragon goes dormant in winter, dying back to the roots. Reduce watering to once every 2 to 3 weeks during dormancy. New growth appears in spring. Harvest: Cut stem tips 4 to 6 inches long. Tarragon does not regrow as vigorously after harvest as basil or mint; harvest conservatively.

Lemongrass (Cymbopogon citratus)

Light: 12 to 14 hours. Water: Keep soil consistently moist. Every 1 to 2 days. Lemongrass is a tropical grass that requires more water than Mediterranean herbs. Fertilizer: 1/2 teaspoon of 10-10-10 per gallon, every 2 weeks during active growth (April through October). Container: 8 to 10 inches. Lemongrass forms large clumps and needs space. Starting: Purchase fresh lemongrass stalks from an Asian grocery store ($2 to $4 for a bundle of 4 to 6 stalks). Trim the top 2 inches and the root end. Place the root end in a jar of 2 inches of water. Roots appear in 7 to 14 days. Transplant to soil when roots are 1 to 2 inches long. Harvest: Cut individual stalks at soil level when they are 0.5 inches thick at the base. The lower 4 to 6 inches of each stalk is the usable portion.

Bay Laurel (Laurus nobilis)

Light: 10 to 12 hours. Water: When the top 2 inches of soil are dry. Every 5 to 7 days. Bay is a slow-growing evergreen tree that tolerates dry conditions. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 6 to 8 weeks. Container: 8 to 12 inches. Repot every 2 to 3 years. Growth: Bay grows 4 to 8 inches per year indoors. A potted bay tree reaches 3 to 5 feet tall after 5 to 8 years. Harvest: Pick individual leaves as needed. Fresh bay leaves are 2 to 3 times more flavorful than dried. Remove the leaf before serving (the leaf is tough and a choking hazard). Purchase: Buy a small nursery plant ($8 to $15). Seeds take 20 to 40 days to germinate and 2 to 3 years to reach harvestable size.

Stevia (Stevia rebaudiana)

Light: 12 to 14 hours. Water: When the top inch of soil is dry. Every 2 to 3 days. Fertilizer: 1/4 teaspoon of 10-10-10 per gallon, every 3 weeks. Container: 6 to 8 inches. Flavor: Leaves are 30 to 300 times sweeter than sucrose, depending on growing conditions. Dry and crush the leaves to use as a sugar substitute. One tablespoon of dried, crushed stevia leaves replaces approximately 1 cup of sugar in tea and beverages (the conversion is less precise in baking because stevia does not caramelize or provide bulk). Harvest: Cut stems back by one-third every 4 to 6 weeks. Dry the harvested stems by hanging them upside down in a warm, dark, well-ventilated area for 3 to 5 days. Strip the dry leaves from the stems and store in an airtight container. Stevia is a tender perennial; it dies below 40 degrees Fahrenheit and must be grown indoors year-round in most climates.

Potting Mix and Container Selection

The potting mix and container you choose affect drainage, root health, and how often you need to water. Standard potting soil straight from the bag is too dense for most herbs and retains too much moisture.

Custom Potting Mix Recipe

Mix the following ingredients in a large bucket: 4 quarts of standard potting mix (Pro-Mix, Miracle-Gro Potting Mix, or equivalent), 2 quarts of perlite (improves drainage and aeration), 1 quart of coarse sand or vermiculite (improves drainage for Mediterranean herbs), and 1/2 cup of worm castings or compost (adds slow-release nutrients and beneficial microorganisms). This mix drains in 30 to 60 seconds after watering, holds adequate moisture for 2 to 3 days between waterings, and provides enough nutrients for 4 to 6 weeks without additional fertilizer. For Mediterranean herbs (rosemary, thyme, oregano, sage), increase the sand or perlite to 2 quarts and reduce the potting mix to 3 quarts for even faster drainage.

Container Materials

Terracotta: Porous clay that allows moisture to evaporate through the walls. Soil in terracotta pots dries 20 to 30 percent faster than soil in plastic pots. Preferred for Mediterranean herbs (rosemary, thyme, oregano, sage) that are sensitive to overwatering. Disadvantage: terracotta is heavy and breaks if dropped or frozen. Plastic: Lightweight, retains moisture longer, inexpensive. Preferred for moisture-loving herbs (basil, mint, cilantro, chervil). Self-watering containers: Have a water reservoir below the soil chamber that wicks moisture upward. Maintain consistent soil moisture for 3 to 7 days between refills. Ideal for basil and mint, which suffer from inconsistent moisture. The Lechuza Classico (8-inch, $25 to $30) and the IKEA Ps Vattenjug (self-watering insert, $5) are reliable options.

Drainage

Every pot must have drainage holes in the bottom. Without drainage, water accumulates at the bottom of the pot, creating anaerobic conditions that kill roots within 48 to 72 hours. If you have decorative pots without drainage holes, place a plastic nursery pot (with drainage holes) inside the decorative pot. Place a layer of gravel or broken pot shards (1 inch deep) in the bottom of the nursery pot to prevent soil from washing out through the drainage holes. Elevate the pot on a saucer or plant feet to allow excess water to drain freely.

Diagnosing the 5 Most Common Indoor Herb Problems

Indoor herbs are susceptible to a predictable set of problems caused by insufficient light, overwatering, and low humidity. Learning to read the symptoms allows you to correct the problem before the plant is lost.

Leggy, Pale Growth

Long stems with large spaces between leaves and pale green or yellow foliage indicate insufficient light. The plant is stretching toward the nearest light source. Move the plant closer to the light fixture (within 6 to 12 inches). If no supplemental light is available, move the plant to the brightest window (south-facing) and rotate the pot 90 degrees every 2 days to prevent one-sided leaning. Pinch back leggy stems to encourage branching. If the plant is too far gone (stems are 12+ inches with only a few leaves at the tip), replace it with a new plant positioned closer to the light.

Fungus Gnats

Tiny black flies (1/8 inch long) hovering around the soil surface are fungus gnats (Bradysia spp.). Their larvae live in the soil and feed on organic matter and root hairs. They are a symptom of consistently wet soil. Control: (1) Allow the top 1 to 2 inches of soil to dry between waterings. (2) Place yellow sticky traps ($4 to $6 per pack of 10) on stakes at soil level; the gnats are attracted to yellow and stick to the trap. One trap per pot catches 30 to 50 gnats per week. (3) Water with a solution of Bacillus thuringiensis var. israelensis (Bti, sold as Mosquito Bits or Gnatrol), 1 tablespoon per gallon of water, applied every 2 weeks for 3 applications. Bti kills gnat larvae in the soil within 24 to 48 hours.

Brown Leaf Tips

Brown, crispy leaf tips are caused by low humidity (common in heated homes during winter, where indoor humidity drops to 15 to 25 percent), inconsistent watering (alternating between bone-dry and saturated), or salt buildup from fertilizer. Solutions: (1) Set the pots on a tray filled with pebbles and 0.5 inches of water. As the water evaporates, it raises the humidity around the plants by 10 to 20 percent. Do not let the pot bottoms sit in the water. (2) Water consistently on a schedule rather than by feel. (3) Every 4 to 6 weeks, flush the soil by pouring water through the pot until it runs out the drainage holes for 30 seconds. This leaches accumulated salts below the root zone.

White Powdery Coating on Leaves

Powdery mildew appears as a white, powdery coating on leaf surfaces, most commonly on basil, mint, and sage. It thrives in still air, high humidity, and crowded foliage. Control: (1) Increase air circulation by spacing pots 4 to 6 inches apart and running a small fan on low speed near the herbs for 2 to 3 hours per day. (2) Remove and destroy affected leaves. (3) Spray with a solution of 1 tablespoon of baking soda and 1 teaspoon of liquid dish soap per gallon of water, applied to all leaf surfaces every 7 days for 2 to 3 applications. The baking soda raises the leaf surface pH, creating conditions inhospitable to the mildew spores.

Sudden Wilting Despite Wet Soil

If a plant wilts and the soil is wet, the roots have been damaged by overwatering or root rot. The roots cannot absorb water even though it is present in the soil. Unpot the plant and examine the roots. Healthy roots are white and firm. Rotted roots are brown, mushy, and may have a foul odor. Trim away all rotted roots with clean scissors. Repot the plant in fresh, well-draining potting mix (see recipe above). Water sparingly for the first 2 weeks to allow the remaining roots to recover. Not all plants survive root rot; basil and mint have a 30 to 40 percent survival rate after repotting, while rosemary and thyme rarely recover once root rot has set in.