Companion planting is a strategic way of gardening in which one type of plant is grown directly beside another plant and benefits it in some way. A prime example of this is planting wasabi, a spicy Japanese horseradish, next to potatoes. The strong, spicy smell of wasabi acts as a natural repellent for pests that often infest potato plants. In turn, the leaves of mature potato plants provide much-needed shade for the wasabi during the hot summer months.
Soak the wasabi rhizomes in bowl of water at least 24 hours before you plant them. Leave the bowl in the refrigerator. This soaking period will prepare the rhizomes for growth.
Cut a hole in the bottom of a plastic planter with a sharp utility knife. The planter will keep the wasabi from overtaking the garden, and the hole in the bottom will allow drainage. The planter needs to be no more than 1 foot in diameter.
Choose a spot in the potato planting site that gets shade. Wasabi is intolerant of full sun, but a few hours of sun per day is safe.
Dig a hole in the chosen spot that is about the same size as the plastic planter. Place the planter in the hole.
Fill in the hole with equal parts compost and soil. Mix the two materials together until they are loose but thoroughly mixed.
Add water to the planting site so that it is moist to a depth of at least 3 inches. Do not let the soil get soggy.
Plant two wasabi rhizomes in the planting site. Bury them just deep enough so they're covered in a thin layer of soil.
Keep the soil moist at all times from spring through fall. Wasabi needs humidity during the warm months in order to thrive.