By September, the corner of the bed where the summer vegetables came out is sitting empty. It's too early to put the next crop in, and left bare, the surface packs down hard under winter rain. Sow field pennycress there and it comes up in fall, covers the ground all winter, and offers the first greens of early spring, before the other vegetables have gotten going. It's a plant people used to gather from the edges of fields, but save the seed and it grows perfectly well in a home garden.
Sowing happens in fall
Field pennycress is a winter annual in the mustard family. It germinates in fall, spends the winter as a rosette with its leaves pressed flat to the ground, and once it has taken the cold and the days lengthen in spring, sends up a flower stalk. That's why the seed goes in during fall. It grows wild in Korea, China, and Japan and does its growing in the cool part of the year, so if your latitude is similar, you can follow the schedule below as written.
- Sowing: September–October in the Northern Hemisphere (shift to March–April south of the equator)
- Growing: ideal 10–20°C (50–68°F); tolerates 2–28°C (36–82°F)
- Harvest: March–April in the Northern Hemisphere, before the flower stalk rises
The seed is tiny, and a thick layer of soil on top will keep the seedlings from breaking through. Rake the surface smooth, broadcast the seed, and press it down lightly with your palm — that's all it needs. Sowing in rows makes spring picking easier. Wait until daytime temperatures have dropped below 25°C (77°F).
Winter asks little of you
It is hardy enough to survive under snow. The rosettes come through the season without straw or row cover. Pile a heavy covering on and the leaves are more likely to go soft. What does matter is moisture right after sowing: if the soil dries out then, germination comes in patchy, so water whenever the surface dries until the seed leaves are up.
Leaves that have wintered over bulk up quickly once the spring sun reaches them. But that same sun raises the flower stalk, and once the stalk is up, the leaves turn tough.
Cut before it bolts
What you eat is the young rosette, before the flower stalk appears. Pass over any plant whose center shoot has started to push upward, and take the ones still lying flat, cutting with a knife just above the root. Don't clear the whole patch at once — harvesting every few days stretches out the eating.
It's easy to mistake for shepherd's purse. Pennycress has bigger, thicker leaves, which is why old Korean names called it the coarse shepherd's purse. Once the pods form, telling them apart is simple: shepherd's purse carries triangular pods, pennycress round flat ones. If you're gathering along field edges or rice-paddy banks, stay off sprayed ground and roadsides.
Blanch it, then dress it
Plants in the mustard family contain glucosinolates. When the tissue is broken, enzymes go to work and turn them into the compounds behind that peppery bite; heat stops the reaction. That's why blanched pennycress tastes mild.
Blanch briefly in boiling water, rinse under cold, and squeeze out the moisture. The vitamin C in the leaves is water-soluble, so the longer you boil, the more of it goes off into the pot. Short is better.
Dress the squeezed greens with doenjang (fermented soybean paste) and perilla oil. Enough of the peppery edge survives that you don't need a heavy hand with the seasoning. A little minced garlic softens the flavor. The leaves are thick enough to hold up in batter, so you can toss them in a Korean pancake mix and pan-fry them thin without their falling apart — fried that way, they're an easy sell with kids. Try piling the dressed greens on a bowl of just-cooked rice, adding just a touch of sesame oil and soy sauce, and mixing it all together.
Save seed before summer
Field pennycress sets seed and dies back before the summer heat arrives. Leave a few bolted plants standing and the pods will ripen, giving you seed to sow again the following fall. The Herb section of the Donguibogam, the seventeenth-century Korean medical compendium, lists this seed as seokmyeongja (菥蓂子) and records its old Korean name as gulgeun-nai ssi, "coarse shepherd's-purse seed." It is described as slightly warm in nature, pungent in taste, and non-toxic. Common everywhere, the text says, and it adds a gathering method: pick the fruit in the fourth or fifth lunar month and dry it in the sun. Note that what's listed is the seed, not the leaf. Accounts in old medical texts don't line up with what we know today, so read them as a record and nothing more.
Pennycress seed oil is high in erucic acid, which is why the plant has also been handled as an oilseed crop. That is a separate matter from the young leaves you eat as greens.
This week, while the soil is still loose from pulling the summer crop, put in a single row. In the Northern Hemisphere, September is the window. Come spring you'll be cutting leaves thicker than shepherd's purse and dressing them with doenjang.
Source: Donguibogam, Herb section, seokmyeongja (菥蓂子)
