Best Grow Lights for Starting Herbs Indoors in Winter

The Short Answer

For a tray or two of herb seedlings in winter, a white LED shop light or LED grow bar is the practical choice. It costs little to run, gives off little heat, and can hang 8 to 12 inches above the plants. A T5 or T8 fluorescent shop light also works well if you already own one, but it has to sit closer, at 4 to 6 inches. Whichever you pick, run it on a timer for 14 to 16 hours a day and keep it adjustable in height. Those two settings do more for stocky seedlings than any feature printed on the box.

Why Herb Seedlings Stretch in Winter

Iowa State University Extension says most herbs need around eight hours of direct light each day when grown indoors. A south-facing window is the best candidate, and a bright east or west window can also work. In December and January, few windows supply that much direct sun, and basil, parsley and cilantro seedlings respond by growing tall and thin.

University of New Hampshire Extension describes the result as stretched, thin plants with lots of space between the leaves. Utah State University Extension names the same cause: poor light intensity produces tall, skinny plants that have trouble staying upright. Seedlings that lean toward the glass are showing that the light is coming from one side only.

New Hampshire’s fact sheet explains the gap with a single comparison. A tomato seedling can collect a full day’s light in about five hours of full sun, while the same plant may need 22 hours under a fluorescent fixture. Indoor lamps are far weaker than the sun, so they must sit close and run long.

Grow Light Types Compared

The University of New Hampshire’s lighting Q&A makes the point that matters most when shopping: failure under lamps is more often about light quantity, meaning intensity and duration, than about light quality, meaning spectrum. Utah State agrees that expensive LEDs or fixtures marketed as grow lights are not necessary and that fluorescent shop lights work well.

Light type	Heat and running cost	Lamp height above seedlings	Suits
White LED shop light or grow bar	Little heat, inexpensive to operate	About 8 to 12 inches	One to several trays, new purchases
T5 or T8 fluorescent shop light	Moderately energy efficient	4 to 6 inches	Racks where the fixtures are already installed
Red and blue (purple) LED	Little heat, inexpensive to operate	Follow the fixture’s instructions	Growers who do not mind the purple cast

The University of Maine Cooperative Extension calls T5 and T8 fluorescent lamps moderately energy efficient for seedlings and notes that this kind of lighting is becoming outdated. It describes LEDs as inexpensive to operate and low in heat. New Hampshire reports that good T8 tubes last 20,000 to 30,000 hours, so an existing fluorescent rack has years of use left and there is no need to replace it.

Purple fixtures combine red and blue diodes, and New Hampshire’s Q&A notes that photosynthesis makes the best use of a red and blue combination. The Maine bulletin still calls full-spectrum, or white, light the best balance for plant growth. The broader comparison for trays of vegetables is in our guide to grow lights for seed starting. If you would rather buy a countertop unit with the light built in, the tradeoffs are in our guide to indoor herb growing systems.

Which Specs Matter on the Box

Color temperature is printed in Kelvin on most bulbs and shop lights. The University of Maine bulletin says seedlings and leafy, vegetative plants prefer a bluer spectrum, which corresponds to 4,000 to 10,000 K, while flowering plants generally prefer a redder 1,000 to 3,500 K. Herbs are grown for leaves, so a bulb labeled cool white or daylight inside that 4,000 to 10,000 K band fits.

Iowa State’s herb guide adds two more things to look for: a full-spectrum lamp and a high-output fixture. Coverage matters as well. A single narrow bar over a wide tray leaves the outer cells dim, and those seedlings bend toward the middle.

The measure that horticulturists use is the daily light integral, the total light a plant receives in a day. New Hampshire’s fact sheet puts the target for seedlings at 12 moles of light per square meter per day, and its Q&A gives a working range of 8 to 14. Few consumer fixtures print this number, so in practice you reach it by keeping the lamp close and the hours long.

How High to Hang the Light

Iowa State University Extension gives the clearest numbers. For most fluorescent fixtures, seedlings should be 4 to 6 inches from the light source. LED fixtures can often be set a little farther away, at about 8 to 12 inches. For established potted herbs under high-output fixtures, the same service suggests placing lights within 6 to 12 inches of the leaves.

Other extension services run fluorescents closer still. Utah State hangs them 2 to 3 inches above the plants and warns about leaf scorch if the lamp runs hot, and University of Illinois Extension says no more than 4 inches away. New Hampshire’s rule of thumb sets the outer limit: keep lamps less than one foot from the tops of the seedlings.

The gap has to stay constant as the plants grow. Hang the fixture from adjustable chains or cables, or do it the other way around and set the trays on blocks or bricks that you remove as the seedlings gain height. If stems stretch anyway, New Hampshire’s advice is to move the lamp closer, run it longer, or both.

How Many Hours to Run It

Set a timer on the first day. Iowa State recommends 14 to 16 hours a day for seedlings and 12 to 16 hours for potted herbs. Utah State gives 12 to 14 hours or more, and Illinois sets a minimum of 10 hours with the option to go up to 16.

University of Maryland Extension advises lighting indoor plants for no more than 16 hours each day in total, counting window light and lamp light together, because most plants require a period of darkness to develop properly. A 16-hour setting, for example 6 a.m. to 10 p.m., sits at the top of every range above and still leaves eight hours of dark.

Setting Up for Stocky Seedlings

Illinois Extension suggests starting herbs such as thyme, rosemary, basil, sage, chives and tarragon in March for transplanting in May, and says most herb seedlings are ready to go outdoors in about 10 weeks. Gardeners who start in January or February are asking the lamp to do even more of the work. Whether to sow at all or buy plants later is covered in herb seeds vs. starter plants.

A short routine keeps growth compact:

1. Switch the light on as soon as the first seedlings emerge. New Hampshire’s fact sheet explains that a seed germinating in low light elongates its stem to reach for the sun.
2. Check the lamp height weekly and raise the fixture or lower the trays.
3. Turn the trays 180 degrees regularly, as Utah State advises, so the edge rows get their share.
4. Give the seedlings moving air. Iowa State asks for good circulation to carry away heat from the fixture, and Clemson’s seed-starting guide places a fan nearby to produce a gentle sway once plants have two true leaves.

The same fixture earns its keep after seed-starting season. It can hold potted kitchen herbs through the dark months or support plants you are overwintering, such as rosemary or bay.

Common Mistakes

The first is waiting. Gardeners often rely on a window through the darkest weeks and add a lamp only after the seedlings have fallen over. The second is hanging the light at a height that feels safe, 18 inches or more, when every source above keeps it within 12. The third is running the light around the clock in the hope of faster growth, which ignores Maryland’s 16-hour ceiling and the dark period plants need. A timer and a tape measure prevent all three.