How to grow basil indoors: give it as much light as you can, keep it warm, water when the top of the mix starts to dry, and pinch it often. UC Master Gardeners say basil can be grown indoors in a south-facing window with at least 6 hours of sunlight, or under fluorescent lights about 6 inches above the plants for 14 to 16 hours a day, and that harvesting can start in about 4 to 5 weeks. Most indoor basil that fails simply doesn’t get enough light.
| Need | What the sources say |
|---|---|
| Light | South window with at least 6 hours of sun, or fluorescent lights about 6 inches above the plants for 14 to 16 hours a day (UC Master Gardeners) |
| Light under LEDs | A daily light integral of about 12.9 mol/m²/day gave high yield and quality in a vertical-farm study (Dou et al., 2018) |
| Temperature | Warm; leaves are damaged below 40°F (UC); seeds germinate best around 75°F (Iowa State) |
| Soil and water | Moist, well-drained soil (NC State); keep plants well watered, as basil is sensitive to drought and water stress (Penn State) |
| Feeding | Avoid heavy nitrogen; too much affects flavor (Iowa State) |
| Pinching | Pinch growing tips and flower buds to promote branching and leafy growth (NC State, Penn State) |
Sources: UC Master Gardeners (Santa Clara County); Iowa State Extension; Penn State Extension; NC State Extension; Dou et al. 2018, HortScience.
Light: The Make-or-Break Factor
Basil is a full-sun herb. NC State and Penn State both list full sun for it, and indoors that is hard to match. UC Master Gardeners give the window threshold: a south-facing window with a minimum of 6 hours of sunlight. East or west windows usually give less, and in winter even a south window gets weaker, shorter days.
Signs of too little light are easy to spot: long gaps between leaf pairs, small pale leaves, stems leaning hard toward the window, and slow regrowth after harvesting. If you see them, move the pot closer to the glass (without letting leaves touch cold glass in winter) or add a grow light. Turning the pot every few days keeps growth even.
Iowa State adds a realistic note: basil grown indoors will have a less intense flavor and fragrance than garden basil. More light helps; so does harvesting before the plants flower.
Growing Basil Under Grow Lights
A grow light makes indoor basil reliable year-round. UC Master Gardeners suggest fluorescent tubes about 6 inches above the plants for 14 to 16 hours a day. Modern LED fixtures do the same job with less heat; follow the maker’s guidance on hanging height.
For readers who use light meters, research gives a target. In a study at Texas A&M, Dou, Niu, Gu and Masabni (2018) grew ‘Improved Genovese Compact’ basil at five daily light integrals (DLI) from 9.3 to 17.8 mol/m²/day. Plants at 12.9, 16.5 and 17.8 had higher photosynthesis and much higher fresh weight (54 to 79% more than at 9.3), and the higher light levels also raised phenolics and antioxidant capacity. The authors suggested 12.9 mol/m²/day as the best balance of yield, quality and electricity cost. For a 16-hour day, that works out to an average of roughly 225 µmol/m²/s at the plants. Our grow light guide explains PPFD and DLI and how to choose a light.
Use a plug-in timer so the light runs the same hours every day, and raise the light as the plants grow.
Seeds, Cuttings or a Supermarket Pot?
- Seeds: sow about 1/4 inch deep (Penn State). Iowa State says basil germinates best at about 75°F, and Penn State notes seeds germinate in 1 to 2 weeks; a heat mat helps in a cool house. Give seedlings bright light right away so they don’t get lanky (Iowa State).
- Cuttings: basil roots from cuttings (UC Master Gardeners). Take a 3 to 4 inch tip without flowers, strip the lower leaves, and root it in water or moist mix, then pot it up once roots form.
- Supermarket pots: these are usually dozens of seedlings crammed together. Divide the clump into a few small groups, pot each one separately, and they will grow far better than the crowded original.
Pot, Soil and Watering
Use a pot with drainage holes, at least 6 inches across for a single plant, and a good bagged potting mix. NC State says basil prefers moist, well-drained soil, and Penn State warns it is susceptible to drought and water stress. In practice, water thoroughly when the top inch feels dry, let the excess drain, and empty the saucer. Under strong grow lights in a warm room, that may be every few days; on a winter windowsill, less often.
Bottom watering works well for herbs and keeps the leaves dry; see our bottom watering guide. Constantly wet soil invites root rot and fungus gnats, so don’t let the pot sit in water.
Pinching and Harvesting for a Bushy Plant
Pinching is what turns one tall stem into a bushy plant. NC State recommends pinching the tips of long stems and any flower buds to promote a branching, bushy form, and Penn State says pinching growing tips delays flowering and promotes leafy growth. When removing the tip of a stem, the side buds just below the cut grow into two new shoots.
- First pinch: when the plant is about 6 inches tall with several pairs of leaves, cut or pinch the top just above a pair of leaves.
- Keep harvesting from the top: always take stem tips, cutting just above a leaf pair, rather than plucking big leaves from the bottom.
- Remove flower buds as soon as you see them. Penn State notes leaf flavor declines after bloom.
- Don’t strip it bare: leave plenty of leaves so the plant can regrow; a common rule is to take no more than about a third at a time.
Iowa State gives one useful harvesting tip: for maximum flavor, harvest when flower buds have started to form but before they open. Once seed forms, much of the flavor is gone.
Temperature and Feeding
Basil likes warmth. UC Master Gardeners say its tender leaves are damaged by temperatures below 40°F, and Penn State notes it is susceptible to cold. Indoors, the main risk is a cold window at night in winter: keep leaves off the glass and away from drafty doors and air conditioning vents.
Feed lightly. Iowa State advises avoiding heavy nitrogen fertilization because too much nitrogen affects basil’s flavor. A balanced liquid houseplant or vegetable fertilizer at half the label rate every few weeks while the plant is growing actively is plenty for a potted plant you harvest regularly. Our fertilizer guide compares the options.
Common Indoor Basil Problems
| Problem | Likely cause | What to do |
|---|---|---|
| Tall, leggy stems with small leaves | Too little light | Sunniest south window or a grow light; pinch tips |
| Wilting with dry soil | Underwatering (basil is sensitive to drought, Penn State) | Water thoroughly; check more often under lights |
| Yellowing, wilting with wet soil | Overwatering, root rot | Let the top inch dry; check drainage |
| Black or dark patches after a cold night | Cold damage (below 40°F, UC) | Move away from cold glass and drafts |
| Yellowing leaves with gray-purple fuzz underneath | Basil downy mildew (NC State, Iowa State) | Remove affected plants; grow resistant cultivars; improve air flow |
| Sudden wilting and stem browning in a young plant | Fusarium wilt (NC State) | Discard the plant and its soil; buy healthy seed or plants |
| Flowers forming | Normal maturity; triggered sooner by stress | Pinch off flower buds; start new plants every couple of months |
| Small flies, sticky leaves or webbing | Fungus gnats, aphids (NC State) or spider mites | Let soil surface dry; rinse leaves; see our neem oil guide |
NC State notes that Master Gardener volunteers trialed basil cultivars resistant to downy mildew and found ‘Prospera’ and ‘Rutgers Obsession’ among the top performers, worth trying if downy mildew has been a problem.
Best Basil Varieties for Indoors
Compact basils suit windowsills best. Penn State lists small-leaf or dwarf types such as ‘Minette’, ‘Spicy Globe’ and ‘Spicy Bush’, alongside large-leaf culinary types like ‘Genovese’, ‘Napoletano’ and ‘Lettuce Leaf’. Genovese types are the classic choice for pesto and respond well to pinching; dwarf types stay neat with less work. Thai basils (‘Siam Queen’, ‘Queenette’) also grow indoors with enough light and warmth.
Basil is an annual, so even well-grown indoor plants eventually decline. Starting a new pot from seed or cuttings every couple of months keeps a steady supply. For growing basil outdoors, see our general basil care guide.
For more herbs and edibles, see our guides to okra. It is also on our list of plants safe for dogs. Basil cuttings also root in a glass of water; see our guides to herbs that grow in water and kitchen plants.
Frequently Asked Questions
Can you grow basil indoors all year?
Yes, with enough light. A south window with at least 6 hours of sun works in brighter months; in winter most homes need a grow light running 14 to 16 hours a day (UC Master Gardeners).
How much light does basil need indoors?
At least 6 hours of direct sun in a south window, or 14 to 16 hours under lights placed close to the plants (UC Master Gardeners). Research on LED-grown basil suggests a daily light integral of about 13 mol/m²/day for good yield and quality (Dou et al., 2018).
How often should I water basil indoors?
When the top inch of soil feels dry. Basil likes moist, well-drained soil (NC State) and is sensitive to drought (Penn State), so check every few days, especially under grow lights.
Why is my indoor basil getting leggy?
Almost always too little light. Move it to a sunnier window or add a grow light, then pinch the stem tips so it branches.
Should I let my basil flower?
Not if you want leaves. Pinch flower buds as soon as they appear; Penn State says leaf flavor declines after bloom. Iowa State says flavor peaks just as flower buds form, before they open.
Why does indoor basil taste weaker?
Iowa State notes basil grown indoors has a less intense flavor and fragrance. More light, avoiding excess nitrogen and harvesting before flowering all help.
Sources
- UC Master Gardeners of Santa Clara County: Basil
- Iowa State University Extension: Growing Basil in the Home Garden
- Penn State Extension: Herb Garden Plants, Basil
- NC State Extension Plant Toolbox: Ocimum basilicum
- Dou H, Niu G, Gu M, Masabni JG (2018). Responses of sweet basil to different daily light integrals. HortScience 53(4): 496-503.