Mustard Microgreens: How to Grow a Spicy Tray

Mustard microgreens are a spicy, fast, forgiving tray: they sprout in about 36 hours at 72°F, tolerate less-than-ideal light, and are ready to cut in roughly 10 to 15 days. Mississippi State Extension lists a 10 to 15 day harvest, Oregon State recommends mustard for a spicy kick, and Maryland Extension notes that mustard and arugula handle a shadier spot well. For anyone with a not-quite-sunny windowsill, mustard is a great pick. The fastest microgreens table shows how its timing compares. New to the method? How to grow microgreens covers the steps every variety shares.

Sowing mustard microgreens

Sow mustard thickly and evenly over a pre-moistened medium, the approach Penn State and Maryland describe for all microgreens, with lower rates in summer than in winter. Check the seed packet for a starting rate; the seed calculator is available for the varieties with a sourced rate. Penn State’s grower table lists a named cultivar, mustard (Red Rain), so look for it if you like to pick by name.

For the medium, Penn State names peat-based mixes, coconut coir and fiber mats, and Maryland suggests a lightweight soilless mix while advising against garden soil. Start each tray clean: seed sold for microgreens or marked untreated (Clemson), a washed tray with drainage holes (Penn State), and fresh water.

Cover and blackout

Mustard germinates quickly: Maryland reports about 36 hours at 72°F for the cabbage family. Cover the tray with a second tray, a lid or plastic to hold in warmth and moisture (Clemson, Maryland), and uncover when the stems are up. In Utah State’s chart, similar brassicas such as radish, kale and arugula stay covered for 1 to 2 days, a handy guide for timing. Penn State suggests keeping seeds in the dark for a few days for a strong start.

Light and watering

Maryland says mustard tolerates less-than-ideal light, but a bright window or grow light still gives the sturdiest tray. Utah State’s chart for other varieties runs 18 hours of light and 6 of dark, and Maryland suggests about 16 hours in total. Aim for 70 to 75°F (Maryland). Bottom-water by setting the tray in a shallow tub until the medium is damp, then drain (Penn State). Keep air moving with a gentle fan or an open window (Maryland, Penn State). The harvest planner turns a sow date into a harvest window.

Harvest

Mississippi State lists mustard at 10 to 15 days, grouped with kale, pac choi, red cabbage, purple kohlrabi and arugula. Maryland’s general size guide is 2 to 3 inches tall, and Purdue and Utah State say to cut when the first true leaves appear. Cut just above the medium with clean, sharp scissors and leave the roots (Penn State). Seedlings do not regrow after cutting (Maryland, Oregon State), so the next tray gets fresh medium. Penn State’s grower table lists mustard (Red Rain) at 201 g per tray, the highest in the excerpt. Store the harvest in a clean plastic bag in the refrigerator (Clemson); Penn State reports 10 to 14 days at 41°F in the dark.

Flavor and color

Oregon State recommends mustard and radish for a spicy kick, and Virginia Tech’s summary of flavor research notes that arugula is peppery or spicy while other brassicas are more neutral. Mustard sits firmly at the spicy end. If you enjoy heat, grow it next to arugula or radish, and balance a mixed bowl with mild kale.

How to use mustard microgreens

• Layer into sandwiches, burgers and wraps for a mustardy kick.
• Scatter over deviled eggs, cheese boards or a sandwich platter.
• Top roast beef, smoked fish or grilled vegetables.
• Toss with a sweet vinaigrette to balance the heat.
• Mix a little into a grain salad rather than using a full handful.

For more ideas, see how to eat microgreens.

Trays and containers

Any shallow, clean, food-suitable tray with drainage holes works, as Penn State describes. Utah State lists standard 1020 trays, 10- or 20-row seed trays, pie tins and takeout containers, and Oregon State notes that drainage holes can be punched with a nail. Wash recycled containers with soap and water (Clemson).

Keep the supply going

Oregon State suggests starting just enough for the household and planting more every few days, a good fit for a strong-flavored green that you want fresh. Maryland and Oregon State both say a bright window or grow lights keep production going indoors all year. Refill with fresh medium after each cut, as Penn State recommends, and rinse the greens just before eating.

Plan your tray