A full head of Japanese Snow Greens with the root still attached on a white background.
Japanese Snow Green leaves resting on a bright pink background with a ruler.
A full head of Japanese Snow Greens with the root still attached on a white background.
Japanese Snow Green leaves resting on a bright pink background with a ruler.

Bok Choy Seeds,
Japanese Snow Green

#OR183 · 200 seeds
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Description

Yukina, or snow mustard, is a traditional vegetable of Yonezawa City in Yamagata Prefecture, especially associated with the Kaminagai area, where it is famously grown under snow using a unique winter system. It is believed Lord Takayama Uesugi encouraged its cultivation in the late 18th and early 19th centuries to help prevent winter hunger, even compiling a food guide that taught edible plants and preservation methods. Sown in late August, harvested from mid-November into early December, and often stored in snow chambers, yukina develops sweeter flavor with exposure to cold. Raw, it is slightly sweet with a mild bitter finish and a texture reminiscent of celery; it can be eaten with miso, in salads, or prepared as fusubedzuke, a traditional salt pickle. A deeply historical, highly practical winter green with a beautiful story and real old-world usefulness.

Plant Details

Botanical Name
Brassica rapa
Life Cycle
Annual
Sun Requirement
4–6 hr.
Days to Germinate
10–14
Days to Maturity
40–45
Planting Depth
¼ in.
Plant Spacing
4–6 in.
Ideal Temperature
60–80°F
Frost Hardy
Yes

Growing Guide

When to Grow

Direct sow after your last frost, or start seeds indoors about 4 weeks before the last frost date and transplant out after it has passed. Resist planting out too early: frost or sustained nighttime temperatures under 50°F may cause young plants to bolt. Sow again in late summer for a fall harvest; in its home region Japanese Snow Green is traditionally sown in late August and harvested from mid-November to early December. For fall sowings, mulch the plants and provide consistent moisture. Heads are ready to cut 40–45 days from sowing.

How to Sow and Plant

  • Direct sow after last frost or start indoors about 4 weeks before last frost date and transplant out after last.
  • Sow seeds 1/4-1/2 inch deep.
  • Ideal germination temperature is 75 F, though they can germinate between 50-80 F.
  • Seeds germinate in 4-7 days.

How to Grow

  • Prefers full sun to part shade.
  • Average moisture needs.
  • Soil should be well drained and ideally amended with well-rotted compost.
  • Plant spacing will depend on the variety; large varieties can be spaced or thinned to 12 inches apart, while the small-headed varieties can be spaced 6 inches apart and micro varieties will only need about 2-4 inches. Rows should be 18-32 inches apart.
  • Bok choy is fairly heat tolerant, but it should be noted that frost or sustained nightime temperatures under 50 F may cause the young plants to bolt, so resist the temptation to plant them out too early. Cold temperatures typically will not cause mature plants to bolt. Sow again in late summer for fall harvest. When sowing in fall, be sure to mulch plants and provide consistent moisture.

PESTS/SPECIAL CONSIDERATIONS

  • Weevils can be a pest of bok choy during winter/spring/ fall crops (they go dormant in summer). Use floating row cover at time of planting to prevent weevils if they are a pest of bok choy in your region.

How to Save Seeds

  • Bok choy is an annual, meaning it will grow and flower and make seed all in one year. Be sure NOT to save seed from prematurely bolted plants as you will essentially be selecting for bolt-prone plants.
  • Allow plants to mature and go to seed, harvest dried pods and crumble the small round seeds into a sealed jar or bag, and store in a cool, dark, dry location.
  • Bok choy will cross pollinate with other members of the rapa species, but will not cross with different species, so it is safe to grow a seed crop of bok choy next to a seed crop of mustard greens (Brassica juncea) for example. Insects cross pollinate the flowers, so be sure to isolate your bok choy from other blooming brassica rapa by about a half mile, or use caging techniques.
  • Allow several of your best-looking bok choy to go to flower in order to provide a nice wide genetic pool and a stronger saved seed over time.

FAQ

Why is Japanese Snow Green called snow mustard?

Yukina, or snow mustard, is a traditional vegetable of Yonezawa City in Yamagata Prefecture, especially the Kaminagai area, and it gets its name from the fact that it grows under the snow using a unique cultivation method. Lord Takayama Uesugi (1751–1823) is believed to have encouraged its cultivation to compensate for the lack of vegetables in winter. Exposure to cold increases its sweetness.

How is Japanese Snow Green eaten?

Raw snow mustard is slightly sweet with a bitter aftertaste and a texture like celery, so it can be eaten raw with miso paste or in salads. A common preparation is fusubedzuke, a pickle made by lightly boiling the greens and pickling them in salt to make a sweet, pungent condiment.

How deep and how far apart should I sow Japanese Snow Green?

Sow ¼ in. deep; seedlings appear in 10–14 days. Thin or space plants 4–6 in. apart, with rows 18–32 in. apart. Give it full sun to part shade, average moisture, and well-drained soil ideally amended with well-rotted compost.

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