Wasabi naturally grows in wet, wooded areas with plenty of moisture in the air and well-draining soil. In the USA, parts of the Pacific Northwest and the Blue Ridge Mountains have the right conditions for growing wasabi. Few other places are naturally suitable for growing the plant.
If you live in a place where the growing conditions are fairly close to what wasabi naturally needs, you may be able to get away without using a greenhouse. If you live in a hot region, use a tarp or sheet to shade the planting bed so it won’t get too hot. If you live in a place with mild cold snaps, cover the plants when the temperature gets cold.
In a greenhouse, it’s still important to make sure the wasabi gets plenty of shade. Situate the wasabi under taller plants or near shaded windows to make sure it isn’t struck by direct sunlight.
Follow label instructions when applying fertilizer.
Planting wasabi near a natural pond or stream is a good idea, since the soil will stay constantly moist, but will naturally also drain well. You could also plant wasabi near a waterfall that will continuously splash on the plant to provide water.
A micro-irrigation system is a good alternative to misting. Watch your plants for wilting (not enough water) and root rot (too much water), and adjust your irrigation accordingly. Because wasabi must be kept wet, it is susceptible to mold and disease. If you see a plant become diseased (wilted and discolored), pull it out right away to prevent it from spreading to other plants. Do not soak the soil or plants with a hose or watering can, as this increases the chance of rot and disease.
When the new plants begin to sprout, space the seedlings about 12 inches (30 cm) apart so they have plenty of room to grow. If you leave them in clumps, many will wilt and die.
