How to Grow Komatsuna

Komatsuna (often called Japanese mustard spinach or tendergreen mustard) is a dark-green, cool-season leaf vegetable indigenous to Japan and Taiwan. Komatsuna leaves have a sweet, fresh taste and a crisp, crunchy texture that you can add to salads and stir-fries, boil, pickle, or add to soups. While komatsuna is known as mustard spinach, it’s not related to common mustard greens, mustard plants, or spinach. Komatsuna is a member of the Brassicaceae family and a variety of Brassica rapa, related to rapini (also called broccoli rabe), turnips, and napa cabbage.

For best results, plant komatsuna in early spring, a few weeks before the last frost date, as soon as you can work the soil in your vegetable garden, or as a fall crop after the weather cools in late summer. Avoid starting komatsuna seedlings indoors for later transplanting since the plants have fragile roots that can’t withstand movement from one location to another.

The optimum soil temperature range for komatsuna plants is 45–95 degrees Fahrenheit. However, temperatures outside of that range aren’t necessarily deadly for the plant. Mature plants can handle brief periods of light frost as low as 20 degrees Fahrenheit, but they will bolt, shoot up flowers, and spoil the flavor in the heat of summer.

After the last frost passes and your soil temperature reaches 45-degrees Fahrenheit, you can plant komatsuna seeds directly into your garden bed:

1. 1. Prepare the soil bed. Komatsuna needs full sun to grow, so choose a site that gets at least six hours of sunlight per day. The plants require a good nitrogen supply, so choose well-draining soil rich in organic matter. Consider amending the soil with nitrogen-rich fertilizer to encourage growth.
2. 2. Begin seeding. Sow seeds about a quarter-inch deep, spacing each seed about six inches apart and in rows eight inches apart.
3. 3. Water. Komatsuna requires routine watering to grow successfully. Keep the soil evenly moist for seed germination.
4. 4. Thin. Once the seedlings are three to four inches high, use shears to thin the seedlings until they are at least 12 inches apart. Thinning the seedlings gives the plant more room to grow and prevents them from competing with nearby plants for nutrients. You can add the thinned seedlings to salads and soups to avoid food waste.

Komatsuna is an unfussy plant that requires only minimal care:

• Water: Komatsuna enjoys moderate water, so keep the soil evenly moist as it grows. Allow the soil to dry between watering to prevent overwatering, which can lead to root rot. Learn more about how to water a garden in our complete guide.
• Prune: Komatsuna will start to bolt in hot weather, sending up flowers and slowing leaf production, making the leaves lose their flavor. Your plant may try to send up flowers periodically while growing, so you’ll need to prune them regularly by pinching off early flower stalks to prevent bolting.
• Protect: Komatsuna can be a target for many common garden pests, including flea beetles and caterpillars. Consider companion planting, natural pesticides, or a floating row cover to deter harmful insects. Companion planting, or intercropping, is a gardening practice in which various crops are planted together to increase growth productivity, ward off pests, suppress weeds, and alter soil chemistry.

You can harvest young komatsuna leaves when they are around three inches tall (about 25 days from seed). Harvest mature leaves at any growth stage. (Komatsuna plants typically mature around 40 days from seed.)

To harvest komatsuna, use shears or a sharp knife to slice outer leaves away from the plant as needed. Leave at least two inches of stem above the ground to allow the plant to continue producing new leaves. At the end of the season, feel free to harvest the entire plant.

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