Arugula microgreens: a peppery brassica that needs little seed per tray

Arugula microgreens are one of the quickest trays you can grow: Utah State University Extension lists them at 6 to 8 days to harvest, no presoak, a 1 to 2 day cover and just 10 g of seed per 1020 tray, with a peppery flavor. The seed rate is the number to get right, because it is far lower than for the other crops in the same table.

The routine otherwise matches any other brassica, so the beginner microgreens method covers sowing, watering and light. What follows is only what is specific to arugula.

Sow far less than you would for broccoli

Utah State’s table gives seeding rates per 1020 tray, which is 10 x 20 in. Arugula sits at 10 g. Broccoli, kale, basil, cilantro and rutabaga are all 28 g, radish is 42 g, sunflower 48 g and pea 150 g. Arugula takes about a third of the seed broccoli does for the same area.

Pouring 28 g onto a tray out of habit therefore puts nearly three times the intended amount of seed down. Penn State Extension and Illinois Extension both describe a target by eye as well, 10 to 12 small seeds per square inch, which is the check to use if your seed lot behaves differently from the one Utah State weighed. The seed density chart shows how to convert a gram figure when your tray is not a 1020.

Penn State’s own rate is a different measure: 10 to 15 g per 12 x 20 in. ten-row tray, which is 240 square inches, not 200. Its arugula result came from that rate, so do not carry the figure over to Utah State’s tray without rescaling.

Overseeding is not only a waste of seed. Penn State Extension advises avoiding overseeding and spacing plants to improve air circulation and reduce humidity, and its damping-off page photographs post-emergence damping-off of arugula in an overcrowded seedbed. If a thick tray starts to collapse at the stem base, damping-off in microgreens covers how to tell it from root hairs and what to change.

No soak, a short cover, a fast finish

Utah State lists arugula with no presoak; only pea and sunflower are soaked in that table. See soaking microgreen seeds for the crops that do benefit.

Stage	Arugula figure	Source
Presoak	None	Utah State University Extension
Covered time	1 to 2 days	Utah State University Extension
Time to harvest	6 to 8 days	Utah State University Extension
Fast brassica group	7 to 8 days at most	Penn State Extension
General stage-one cover	2 to 3 days	UC ANR Coastal Gardener

Utah State and UC ANR disagree on the cover. Utah State’s 1 to 2 days is the shortest in its table, shared with kale, radish and rutabaga, while UC ANR describes 2 to 3 days of weighted cover for crops in general. Because the sprouts are fast, lift the cover as soon as the tray has germinated rather than holding to a number; blackout time by crop explains the cue. Utah State’s 6 to 8 days and Penn State’s 7 to 8 describe the same fast group, and a cool or dim room pushes the tray later. Harvest dates for a mixed shelf are in the growing timeline planner.

Utah State describes the flavor as peppery. Anyone after more heat should try mustard microgreens.

What a tray yields

Penn State Extension weighed greenhouse trays over 14 to 28 cycles in 2016-17, at 10 to 15 g of seed per ten-row tray and a two-week cycle with no supplemental light. Arugula averaged 147.6 g per tray, above the 136 g average across all the varieties in that trial. Mustard (Red Rain) reached 201 g and cilantro 47 g. Treat these as greenhouse averages, not a windowsill promise; yield per tray by crop and tray size converts them to other trays.

Cutting and keeping it

Illinois Extension cuts 1/4 to 1/2 in. above the soil line and Purdue Extension about 1/4 in., both with scissors or a sharp knife. Arugula, like most microgreens, is cut at the base, which removes the growing point, so a second flush is not expected.

Purdue says freshly harvested microgreens last about a week stored unwashed in the refrigerator and washed just before eating. A packaging study on arugula microgreens kept at 5 °C found them safe for consumption within ten days in open, vacuum-sealed and modified-atmosphere bags. Open packaging gave less weight loss and slower chlorophyll degradation, while vacuum-sealed samples lost sensory quality from the fifth day. So the week is the home expectation; ten days at 5 °C is what that study measured. The full washing question, where extension services differ, is in how to harvest and store microgreens.

If you want the mature plant afterwards, arugula in containers covers it.

Sources

• Utah State University Extension: Grow Your Own Microgreens — arugula seeding rate, presoak, covered time, days to harvest and flavor.
• Penn State Extension: Growing Microgreens — seeding rate per ten-row tray and the measured yield table.
• Penn State Extension: The ABCs of Microgreens — the fast brassica group.
• Penn State Extension: Safeguard Your Seedlings from Damping-Off — overseeding and the arugula photograph.
• UC ANR Coastal Gardener: Your Indoor Winter Garden — the two-stage cover.
• Illinois Extension: Growing Microgreens — seeds per square inch and cut height.
• Purdue Extension: Grow Microgreens at Home — cut height and shelf life.
• Postharvest quality of arugula (Eruca sativa) microgreens in different packaging — storage at 5 °C.