How much light do herbs need? Most culinary herbs need the equivalent of at least 6 hours of direct sun a day, which indoors means a daily light integral (DLI) of about 10–17 mol/m²/day, or roughly 200–400 µmol/m²/s of PPFD for 14–16 hours under grow lights. Basil, rosemary, thyme, oregano and sage sit at the high end; parsley, cilantro, chives, mint and dill tolerate the lower end. A south-facing window in winter rarely gives enough, so most indoor herbs grow better with an LED.
Key takeaway: If herbs stretch, lose color or grow slowly, the light is too weak. Give sun-loving herbs at least 12 mol/m²/day and leafy herbs at least 8–10.
| Herb | Light need | Target PPFD (µmol/m²/s) | Approx. DLI |
|---|---|---|---|
| Basil | High | 250–400 | 12–17+ |
| Rosemary, thyme, oregano, sage | High | 300–500 | 15–20 |
| Parsley | Medium | 200–300 | 10–14 |
| Cilantro, dill | Medium | 200–300 | 10–14 |
| Mint, chives | Medium to low | 150–300 | 8–14 |
| Seedlings and cuttings | Low | 100–200 | 6–10 |
How Much Light Do Herbs Need Indoors?
Penn State Extension notes that most herbs grown indoors need bright light, ideally a south or west window with at least 6 hours of sun, and that supplemental lights help in winter. Window light drops sharply even a few feet from the glass, and winter days are short, so an indoor windowsill often supplies only a fraction of what herbs get outdoors. Virginia Cooperative Extension explains how to turn light readings into DLI, which is the best way to compare. See PPFD and DLI and do hydroponic plants need sunlight.
Basil Needs More Light Than You Think
Basil is the herb most often grown under too little light. An e-GRO alert on slow basil growth points to low light as a common cause in greenhouses, and growers often target a DLI of 12 or more. Under a weak kit light, basil gets tall and thin with small, pale leaves. Give it 250–400 µmol/m²/s for 14–16 hours. See Thai basil hydroponics and pruning hydroponic basil.
Mediterranean Herbs
Rosemary, thyme, oregano, sage and lavender come from sunny, dry climates. Indoors, they need the brightest spot and do best under strong LEDs. Low light makes them weak and prone to powdery mildew and root problems. Keep them a bit drier and warmer than leafy herbs. See rosemary and thyme.
Leafy Herbs
Parsley, cilantro, chives, mint and dill grow in partial shade outdoors and handle lower light indoors. They still grow faster with more light, but too much heat with high light can make cilantro and dill bolt. Mint spreads fast even in moderate light. See best herbs for hydroponics.
How Much Light Do Herbs Need Under LEDs?
Under LED grow lights, the answer is easier to control. Set a fixture to deliver the target PPFD at the canopy, then pick the hours to reach the DLI you want. For example, 250 µmol/m²/s for 16 hours gives about 14.4 mol/m²/day, and 300 for 14 hours gives about 15.1. Hang most LEDs 12–24 inches above the plants and measure at the edges. See LED watts per square foot and light hanging height.
Photoperiod for Herbs
Most herbs are happy with 14–16 hours of light. Basil, which can flower under long days, grows well at 16 hours if you pinch flower buds. Avoid 24-hour light, which stresses some plants and wastes power. See light schedule and photoperiod.
Signs of Too Little Light
- Long gaps between leaves (stretching).
- Small, thin, pale leaves.
- Plants leaning hard toward a window.
- Weak aroma and flavor.
- Slow regrowth after harvest.
Signs of Too Much Light
- Bleached or yellow-white patches on top leaves.
- Leaf edges curling up.
- Fast bolting in cilantro and dill.
- Crispy tips near the light.
See light burn and photobleaching.
Window Light vs Grow Lights
A south window in summer can supply enough light for most herbs. In winter, north of about the 35th parallel, even a south window often gives only 5–10 mol/m²/day. East and west windows give less. North windows are too dim for most herbs. Adding a small LED for 12–16 hours a day solves the shortfall.
Light and Flavor
Stronger light usually means stronger flavor and aroma, because plants make more essential oils. Herbs grown in dim conditions often taste mild. If your basil tastes weak, more light is the first fix to try.
Light and Feeding Work Together
More light means faster growth and more nutrient demand. Raise EC slightly as you increase light, and keep pH in range. See nutrients for herbs.
How Much Light Do Herbs Need in Hydroponic Systems?
The answer to how much light do herbs need doesn’t change much between soil and hydroponics, but hydroponic herbs often grow faster, so they show light shortages sooner. In a countertop kit, the built-in light usually covers small herbs such as parsley, chives and young basil, but larger basil and woody herbs outgrow it. In a shelf or tent setup, plan your light for the most demanding herb in the group, which is usually basil. In a greenhouse, winter light may fall well below the targets in the chart, so supplemental LEDs keep growth steady.
How Much Light Do Herbs Need by Season?
Outdoors in summer, most US locations get 30–50 mol/m²/day of sunlight, far more than herbs need. In winter, the same spot may get under 10, and indoors behind glass much less. That’s why herbs that thrive on a summer patio sulk on a winter windowsill. Indoors, use a timer and an LED so light stays constant year-round.
How to Measure Light for Herbs
- Use a quantum PAR meter or a calibrated phone app with a diffuser.
- Measure at the top of the plants at midday or with lights on.
- Multiply PPFD by hours of light and by 0.0036 to get DLI.
- Compare with the chart above for each herb.
- Recheck as plants grow closer to the light.
See measuring PPFD with a phone.
Grouping Herbs by Light
Put basil and Mediterranean herbs in the center of the light, where PPFD is highest, and leafy herbs such as parsley, mint and chives near the edges. This simple layout answers how much light do herbs need for a mixed garden without buying separate fixtures. Turn pots weekly if one side faces a window.
A Quick Rule of Thumb
If you only remember one thing about how much light do herbs need, remember this: if a plant is stretching, give it more light before you change anything else. Most indoor herb problems start with light.
FAQs
How many hours of light do herbs need?
About 6 hours of direct sun, or 14–16 hours under grow lights.
Can herbs grow in a north window?
Usually not well; add a grow light.
What PPFD does basil need?
About 250–400 µmol/m²/s.
Do herbs need darkness?
Yes; give 8–10 hours of dark each day.
Which herbs need the least light?
Mint, chives and parsley tolerate lower light.
Are kit lights enough for herbs?
For a few small herbs, often yes; for big basil plants, often not.
Sources
- Penn State Extension — Growing Herbs Indoors
- Virginia Cooperative Extension — Calculating and Using Daily Light Integral (DLI)
- e-GRO — Slow Basil Growth
- Clemson Cooperative Extension — Basil
- Photo credits (Wikimedia Commons, edited with titles): Click & Grow Smart Garden 27 by Janar Raidla (CC BY-SA 4.0); Click & Grow Smart Garden 27 by Janar Raidla (CC BY-SA 4.0); Ocimum Basilicum leaf lighted by the left by BernaBotto (CC BY-SA 4.0); Basil plant in a pot 02 by Netha Hussain (CC BY-SA 4.0); Coriander Green Seeds (Coriandrum sativum) in Shimla by Sapna Sony (CC BY-SA 4.0)