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How to Grow Mizuna (Japanese Mustard)

Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.

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I love spicy foods so it should come as no surprise that I love arugula. I also love mizuna, a Japanese green that has a peppery kick to it.

What is Mizuna?

Mizuna (Brassica rapa var. japonica) is a cool season green which looks and tastes very much like arugula but is actually a member of the cabbage family. It is native to Japan where it is used in soups, stir fries, hot pots and is also pickled. The taste is peppery.

The plants are biennial but are usually grown as annuals. They grow in a rosette of leaves that is 12 to 18 inches tall and 10 to 15 inches wide. The leaves are usually dark green but there is also a variety that has dark purple leaves. Both have deeply serrated edges. The plants will bolt (flower then produce seeds) as the hot temperatures of summer set in. Most gardeners harvest the leaves before the plants flower. If you allow the plants to bloom, the flowers are also edible.

The flowers are also edible.

The flowers are also edible.

How to Grow Mizuna

Mizuna is a cool season plant that is best grown in the spring or the fall. It can also tolerate a bit of shade only needing 3 to 4 hours of sunlight each day. Planting it in partial shade or where a taller plant provides some shade can help extend the growing season when warmer weather comes.

Mizuna is a heavy feeder meaning it can easily exhaust the nutrients in the soil. Be sure to work in a good amount of compost or well-rotted manure into your soil before planting. Using legumes as a cover crop which is then tilled into the soil before you plant your mizuna will also add much needed nitrogen to your soil. Legumes fix nitrogen into the soil by means of symbiotic rhizobia bacteria in their roots. The bacteria produce nitrogen. When the legumes die or are tilled into the soil that nitrogen is released into the soil for use by other plants.

Mizuna needs 1 inch of water each week. If there is not enough rain, you will need to water your garden to keep the soil moist. If the plants are too dry, they will not grow or will grow slowly. Always water your plants at the roots. Drip irrigation is best but if you have a small garden and hand water, use a watering wand. A watering wand is a nozzle that has a long handle that allows you to water close to the roots. A thick layer of mulch (2 to 3 inches) will help keep the soil moist and prevent weed seeds from germinating and competing with your plants for water and nutrients.

A salad made with mizuna and shaved daikon radishes.

A salad made with mizuna and shaved daikon radishes.

How to Grow Mizuna From Seed Outdoors

You can direct sow your seeds in your garden in the spring when the soil temperature reaches 55⁰F - 60⁰F. Plant your seeds ¼ inch deep and 1 inch apart in rows 18 to 24 inches apart. They should germinate quickly, within 4 to 8 days. When the seedlings have grown to 2 to 3 inches tall, thin them to 6 inches apart. You can sow seeds every two weeks until summer for a continuous harvest.

For a fall harvest, sow your seeds in late summer. In my zone 6 NJ garden, that means August. Plant them the same ¼ inch deep and 1 inch apart in rows 18 to 25 inches apart. Because the soil is warmer, they will germinate more quickly, usually within 4 days. When the seedlings have reached a height of 2 to 3 inches tall, thin them to 6 inches apart. You can sow seeds every two weeks until late fall for a continuous harvest.

How to Start Mizuna Seeds Indoors

Mizuna seeds can be started indoors 3 to 4 weeks before your last frost. Sow your seeds ¼ inch deep in containers. Ideal soil temperature for indoor germination is 70⁰F to 75⁰F. A heat mat will help to keep the soil warm. Germination should occur in 4 to 8 days. You can transplant your seedlings outdoors 1 month after germination. Plant them 6 inches apart in rows 18 to 24 inches apart.

How to Harvest Mizuna

Harvest your mizuna using a sharp knife. Cut the leaves off at soil level. You can harvest the plants as either baby greens or mature greens. For baby greens, harvest when the plants are 3 to 6 inches tall, about 20 days. For mature greens, harvest when the plants are 12 to 18 inches tall, about 40 days. When harvesting mature greens, you can either pull up the entire plant or just cut some of the leaves for a cut-and-come-again harvest.

How to Store Mizuna

Freshly harvested mizuna leaves can be stored in a plastic bag in the crisper drawer of your refrigerator. They will stay fresh for 4 to 5 days.

Questions & Answers

Question: How deep are the roots of Japanese Mustard? Can I use a very shallow planter, 4", for Japanese Mustard?

Answer: 4 inches is way too shallow, even for mint. Containers that are 6 inches or deeper are the best for healthy root growth. Healthy roots produce healthy foliage resulting in bigger and better harvests.

© 2020 Caren White