Grow Lights for Microgreens: Hours, Setup and Timing

Grow lights give microgreens steady, even light for 16 to 18 hours a day, and extension guides describe two simple schedules: Utah State keeps lights on for 18 hours and off for 6, while the University of Maryland aims for about 16 hours of total light per day from any source. Oregon State Extension adds that fluorescent lights work well for the best and most even growth, though a bright window also does the job. Microgreens are a low-light crop, so a basic setup is enough. This guide covers how long to run lights, what kind to use and how lights fit into the tray schedule.

How much light microgreens need

Penn State Extension calls microgreens a low-light crop, with a daily light integral (DLI) below 20 mol/m2/day. Cornell Garden-Based Learning says they do great in indoor spaces without special light requirements. In practice that means you do not need high-powered equipment, and the time the light is on matters as much as its strength.

Hours of light: 16 or 18

The two sourced schedules sit close together.

Both work for a home tray. A timer makes either schedule effortless: set the lights to come on in the morning and switch off in the evening, and the tray gets a regular dark period every day. “From any source” in the UMD guidance means window light and grow lights count together, so a tray by a bright window can take its hours from both.

What kind of lights

Oregon State says fluorescent lights work well for the best and most even growth. UMD and Oregon State both describe grow lights or a bright window as the way to keep production going through the year.

If you start with a window, you can add lights later without changing anything else in the method. See microgreens on a windowsill for the window-only setup.

When the lights go on

Light starts after the blackout. Seeds germinate in the dark under a cover (USU, PSU), so the tray sits covered for the first days: 1 to 2 days for radish, kale and arugula, 2 to 4 for broccoli, 3 for pea and sunflower, 4 to 7 for basil and 7 to 14 for cilantro (USU). When the cover comes off, the tray goes under the lights and the timer takes over. The blackout method explains the cover, the weight and the timing.

Temperature under lights

Utah State gives a full daily pattern for a lit setup: 74 F for germination, 72 F with the lights on and 68 F with the lights off. UMD gives 70 to 75 F, Penn State 60 to 75 F for soil and 60 to 70 F for air, and Purdue 68 to 72 F. A room at about 68 to 72 F matches all of them. Keep the tray clear of HVAC vents and the temperature swings near windows (Purdue), and let a gentle fan breeze move the air (UMD).

Setting up a light shelf

1. Pick a spot. A shelf, a table or a counter with room for the tray and a fixture above it.
2. Hang or mount the light above the tray so it covers the whole surface evenly. The goal is the “best and most even growth” Oregon State describes.
3. Add a timer. Set it for 16 or 18 hours of light.
4. Add a fan if you like. UMD suggests a gentle breeze to keep air moving around the dense cluster of plants.
5. Place a tub or second tray nearby for bottom watering (watering microgreens).

How lights fit the growing cycle

A typical run looks like this.

Microgreens go from seeding to harvest in 7 to 21 days, so a lit tray needs light for just a week or two. Arugula takes 6 to 8 days, radish 8 to 12 and cilantro 21 to 28 (USU), and the harvest planner shows the cut date for each.

Lights year-round

Light makes year-round growing straightforward. UMD says baby greens can be grown year-round with supplemental light, and both UMD and Oregon State describe grow lights or a bright window as the way to keep indoor production going. Pair that with succession planting: Oregon State suggests starting just enough for two people to eat and planting more every few days. A lit shelf with two or three trays at different stages gives you something to cut every few days.

Low-light friendly varieties

If your lighting is modest, UMD notes that arugula and mustard tolerate less-than-ideal light. They are quick too: arugula can be cut in 6 to 8 days (USU). Sunflower and pea shoots are other popular choices, each ready in about 8 to 10 days. For a gentler start, see the microgreens for beginners collection.

Next steps

For the whole method, start with how to grow microgreens. If you are choosing supplies, growing microgreens at home lists everything for a first tray, and growing medium for microgreens helps you pick what goes in it. To work out how much seed a tray needs, use the seed calculator.