Herbs and leafy greens are the easiest crops to grow under LED lights. Give lettuce, spinach and kale about 14 to 16 hours of moderate light a day, keep basil to around 10 to 12 hours so it does not flower early, hang the light so leaves get an even, gentle intensity, and harvest often.
Why herbs and leafy greens suit LED lights
These crops are grown for their leaves, so they never need the strong, high-energy light that flowers and fruit demand. They grow fast, stay compact and can be harvested in weeks. That makes them ideal for a shelf, a countertop, a small grow tent or a simple hydroponic jar. If you are new to indoor growing, start here. See who would use an LED grow light.
The easiest plants to start with
Leafy greens
- Lettuce in loose-leaf, butterhead and romaine types. Loose-leaf lettuce can be cut again and again.
- Spinach, which likes cooler conditions.
- Kale and other leafy brassicas, which are hardy and productive.
- Arugula and mustard greens, which are very fast.
Herbs
- Basil, the favorite, which wants warmth and plenty of light.
- Mint, parsley, cilantro and chives, which are productive and forgiving.
- Thyme, oregano and rosemary, which grow more slowly and like drier conditions.
How much light do they need?
Leafy greens saturate at moderate light. A review of lettuce research found 150 to 300 µmol/m²/s optimal under artificial light, and a study of iceberg lettuce in a vertical hydroponic system found the best fresh weight at 200 µmol/m²/s for 16 hours, which is a daily light integral of 11.5 mol/m²/day. A higher dose of 14.4 reduced weight and leaf area. Herbs are commonly listed at slightly higher, about 200 to 400 µmol/m²/s, or a daily light integral of about 14 to 20.
| Crop | PPFD (µmol/m²/s) | Hours a day |
|---|---|---|
| Lettuce and spinach | About 150 to 300 | 14 to 16 |
| Kale and other greens | About 200 to 300 | 14 to 16 |
| Basil | About 200 to 400 | About 10 to 12 |
| Mint, parsley, cilantro, chives | About 200 to 300 | 12 to 16 |
More light does not always mean more growth. Once leaves have all they can use, extra intensity wastes power and can cause tipburn or early flowering. Read daily light integral explained and what PPFD is.
Hours of light, and how to stop herbs flowering early
Most greens do well on 14 to 16 hours a day with a dark period. Herbs are different because a flower is a setback: leaves of a flowering herb often turn bitter and growth slows. Basil is the classic example. Some basil, such as Genovese, is day-neutral and flowers whatever the day length. Others, such as Thai and holy basil, flower faster when days run longer than about 12.5 hours. Warm temperatures above about 80°F can also push basil to flower. To keep herbs leafy:
- Keep basil to around 10 to 12 hours of light.
- Keep the room steady, in the 70s°F for basil.
- Pinch off flower buds as soon as you see them.
- Harvest regularly, because cutting encourages bushy growth.
Read how many hours of light plants need.
Setting up the light
- Choose a full-spectrum white LED. It lets you see leaf color, an early warning for nutrient problems. See full spectrum LED grow lights.
- Put it on a timer. Consistent hours matter more than perfect hours.
- Set the height or dimmer to a gentle intensity at first. Read how far to hang LED grow lights from plants.
- Cover the whole growing area evenly. Corners that get less light grow slowly.
Growing methods that work
In soil or a soilless mix
Plant in pots or trays of good potting mix with drainage. Keep the mix evenly moist. Leafy greens are shallow-rooted, so wide, shallow containers work well.
In a simple hydroponic jar
Leafy greens and herbs are the best crops for the Kratky method, a passive hydroponic system with no pumps, because lettuce reaches maturity before the nutrient solution runs out. See LED grow lights for hydroponics.
Sow, thin, harvest
- Sow thickly, then thin to give each plant room. Crowded plants stretch.
- Harvest the outer leaves of lettuce and kale first and let the center keep growing.
- Cut herbs above a pair of leaves to encourage branching.
- Never take more than about a third of a herb at once.
- Sow a new batch every two to three weeks for a steady supply.
Temperature and airflow
Lettuce and spinach prefer cooler conditions than basil. A room that is comfortable for you is usually fine for greens; basil likes it warmer. A gentle fan keeps air moving, which strengthens stems and reduces damp, and it helps prevent tipburn.
Common problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Tall, thin, pale plants | Light too weak or too far | Lower the light or raise the dimmer |
| Herbs flowering early | Long days or heat | Shorten to 10 to 12 hours; cool the room; pinch buds |
| Brown edges on young lettuce leaves (tipburn) | Too much light with poor airflow | Dim the light, add a fan |
| Yellowing leaves | Too little feed or overwatering | Check watering; feed lightly |
| Slow growth | Too cold or too little light | Check temperature and hours |
A simple weekly routine
- Daily: look at the plants, check the water level or soil moisture and make sure the light and the timer are working.
- Every few days: harvest what is ready, and pinch off flower buds on herbs.
- Weekly: rotate trays so that every plant gets the same light, thin new seedlings and wipe up any spilled water.
- Every two to three weeks: sow a new batch so there is always something ready to cut.
Sample setups
| Space | What you could grow | Light approach |
|---|---|---|
| A kitchen shelf | Basil, parsley and a tray of lettuce | A small, dimmable light on a timer for 14 hours |
| A 2 x 2 foot tent | A tray of mixed greens and a few herbs | One light, dimmed to a gentle level, with a fan |
| A hydroponic jar | One lettuce or one basil per jar | A light above the leaves; cover the jar |
Questions about herbs and greens
Why is my basil tall and leggy?
It is reaching for light. Lower the light, raise the dimmer or give it more hours, and pinch the tips to encourage bushy growth.
Can I grow herbs under any LED light?
Basic LED lights will grow herbs slowly. A full-spectrum grow light gives better, more even growth, and it lets you see the leaf color.
How long until the first harvest?
Many leafy greens can be harvested within a few weeks of sprouting, especially if you cut the outer leaves. Herbs usually take a little longer. The seed packet gives days to maturity.
Key takeaways
- Lettuce, spinach, kale, basil, mint and parsley are the easiest crops under LED lights.
- Leafy greens like about 150 to 300 µmol/m²/s for 14 to 16 hours.
- Keep basil to around 10 to 12 hours and pinch flower buds to stop early flowering.
- Sow every two to three weeks and harvest often.
- Use a fan and a dimmer to avoid tipburn and stretching.
Why LED lights make this easy
LED lights are efficient, run cool at the plants and can be dimmed to the gentle level that greens like. My LED Grow Lights have a dimmer switch and full-spectrum white light, so you can see exactly how your leaves look. See all of our LED grow lights, or return to what to grow under LED lights.
Related reading
- Growing Tomatoes and Peppers Under LED Lights
- Growing Citrus Indoors Under LED Lights
- Back to What to Grow Under LED Lights