Latin Name: Wasabia japonica ‘Daruma’
Initial Instructions: As home cultivation of wasabi is a relatively recent practice, we recommend growing in containers until you can determine hardiness, shade, and watering requirements and how your own garden and climate suit these. Planting medium should be well-drained with ample organic matter. Work in 10-12 inches of compost to a soil depth of 8-10 inches. A neutral or slightly acidic soil pH of 6-7 is ideal. You may provide a base layer of gravel or sand for drainage. Container size should be 10 inches or larger (at least a 2.5 gallon nursery pot) with enough depth to allow for rhizome development. Rhizomes will typically reach 4-8 inches in two years before harvest but can grow larger. Dig a hole about twice the size of the rhizome you’re transplanting, leaving 1/2 inch of the crown exposed above the soil level. Do not bury the crown! Spread out its roots slightly before backfilling the hole and gently pressing into place. Water in well, ensuring that the plant does not sit in its drainage water, which can lead to root rot. Water regularly before the soil dries completely, especially while your roots are just getting established.
Cultivation: Wasabi grows best in full shade with steady temperatures between 50-60º F, though our Daruma strain is more tolerant of heat and light. Temperatures below 43º F slow growth, while 27º F and below can kill the top growth or even the entire plant. Heat damage can occur when air temperatures rise above 82º F, as well as increased pest and disease incidence. If you’re outside of frost risk, an ideal spot to set out would be a northern exposure and/or well-shaded spot, perhaps utilizing 75% shade cloth. Irrigate regularly with cool water (45-59º F), misting as needed to keep plants cool and moisten wilted leaves. Mulch can increase moisture retention. Leaves that remain wilted for a week should be removed to deter pests and lower risks of disease. In areas with hard frost, wasabi may thrive indoors; in our zone 7 gardens, container-grown wasabi has overwintered in an unheated greenhouse, as well as acclimating itself to full sun conditions. Stability in growing conditions throughout the seasons provides uniform, high-quality yields. Still, the plants are surprisingly tolerant of variable conditions once established, and will let you know when they’re too far out of their comfort zone. Keep the growing medium weed-free and fertilize minimally with a balanced, all-purpose fertilizer until you figure out what works for you; it is better to under-fertilize than over-fertilize. Fertilizers or foliar sprays high in sulfur are said to improve the flavor of the rhizome.
Size/Spacing: 8-18 inches tall, 12 inches apart
Pests & Diseases: Subject to pests and diseases of the brassica family; aphids, cabbage and alfalfa looper larva, crane fly larva, and slugs can all damage crops. Biological controls such as beneficial insects, spraying aphids off with a hose, hand removal of slugs, and pruning of wilted or diseased foliage can decrease these pressures. Careful use of insecticidal soaps or appropriate insecticides may be necessary. Your best defense is maintaining the stable, cool temperatures and steady irrigation wasabi prefers; variable conditions can drastically increase the incidence of pests and disease. While some growers report success replanting year-after-year from divisions, it is recommended to limit vegetative propagation to 3 consecutive years to minimize the risk of disease. You could then use fresh planting stock or learn more about attempting propagation from seed.
Soil Type: Well-drained, very rich in organic matter
Light Requirements: Full to partial shade, full shade preferred
Hardiness: Hardy to at least 27º F. If your winter lows are below 30º F, greenhouse or container growing is encouraged.
Harvest: You may harvest a 4 inch or larger rhizome and multiple divisions for replanting 18-24 months after planting. Harvest select petioles (leaf stems) and leaves in the meanwhile for a mild wasabi heat used fresh in salads, sautéed, pickled, or as garnishes; overharvest of leaves can lead to slow rhizome development, so use sparingly. Hand dig your rhizome in the fall or spring, when temperatures are cool and moisture is high. You can pull off the plantlets that will have formed around the crown, replanting those into 6 inch pots, then up-potting into full-sized containers (as mentioned above) the following year to expand your wasabi planting.

Consult the Pacific Northwest Extension and its member Washington State University for more information: http://agsyst.wsu.edu/wasabi.html