How to grow microgreens hydroponically

What you need

Grow channels, reusable grow mats, a reservoir with an irrigation pump and a stir pump, timers for water and lights, grow lights, fans, and a pH and EC meter.

The AutoKit puts all of that on one mobile rack, with watering and lighting on timers. The StarterKit is the smaller mobile option. For a full production room, see our microgreen grow racks.

Hydroponics Parameters

Step 1: Fill the reservoir

Tap water or reverse osmosis water both work. Take an EC reading of the water first. Add nutrients until you read 1200 above that number, then balance the pH to 5.8.

Microgreens don't need much. Any hydroponic nutrient mix works at that strength.

Step 2: Soak the mats

Soak the mats in planting water for about an hour so they are fully saturated. Sanitized mats push the pH up while they soak, so test it and bring it back to 5.8 right before you plant.

Step 3: Plant

Weigh the seed for each channel ahead of time. We use small ramekins sorted by variety and planting date, then pour each one into a seed shaker.

1. Lay the soaked mat in the channel and add a little more water.
2. Roll it flat with a short piece of PVC pipe, starting at the drain end.
3. Shake the seed edge to edge. Break up any piles with your fingers.
4. Mist the seed. We don't pre-soak seed, so this is what wets the shells.
5. Put the cover on and move the channel to germination.

Seed per 9 x 30 in mat: arugula 22 g, broccoli 30 g, radish 40 g.

Step 4: Germination

With a snug cover, you don't touch the channels again until germination is done. No extra water and no weights. Keep a temperature and humidity sensor near the channels and check the highs and lows. If the room stays at 65 to 83°F and 40 to 60% humidity, that is all this stage needs.

Most varieties germinate within about 72 hours. Uncover when most seedlings are starting to stretch for light. Wait too long and they get leggy under the cover.

Root hairs or mold?

White fuzz in the first few days is usually root hairs. Spray it with water. Root hairs disappear. Mold stays, and it spreads across the stems and the mat instead of growing out from a root.

If germination is poor

Check these in order before you replant.

• Seed quality. Old or badly stored seed may not germinate in a perfect room.
• Planting water pH. If it isn't at 5.8, seeds struggle.
• Heat. Above 85°F (29.5°C) stops germination and can kill new seedlings.
• Air movement. Fans, heaters or AC blowing on the channels dry them out.

Step 5: Under the lights

Before the channels go under lights, slide a drain wick under each mat and out the drain end, a few inches past the spout.

Young plants dry out fast because most of the mat is open to the air. As the canopy fills in, water less often and turn the fans up. Water droplets on the leaf edges are the first sign of overwatering. Adjust to what the plants look like, not the day on the chart.

Step 6: Dry down and harvest

Stop watering 6 to 8+ hours before harvest, longer in some rooms. Before you cut, check three things: no droplets on the leaves, the wicks have stopped dripping, and no water under the mat.

On harvest day, unplug the pump first. Pull the wicks, pull the mats, hang them by the corner grommets and cut from the top down into a clean tote. Get the greens into the cooler at 32 to 36°F.

What one 9 x 30 in mat yields per harvest: arugula about 1.1 lb (500 g), broccoli about 1.1 lb (500 g), radish about 1.8 lb (820 g). Results vary by grower and setup.

Step 7: Clean the mat and plant again

Hang the mats in the sun until the stems and roots are crispy. Scrape everything off with a trowel. Then sanitize, rinse and reuse. We use hydrogen peroxide or a diluted bleach solution.

Our reusable grow mats are solution-dyed PET fiber and last 70+ uses.

Which crops

Arugula, broccoli, radish, mustard, kale, cabbage, bok choy and the rest of the planting table in the Grow Guide, each with its seed weight and grow time. We don't recommend peas on our mats.