Although it’s one of the most difficult plants to grow, wasabi can be successful in your garden by caring for it meticulously and providing the optimal location. Begin germinating your seeds overnight in a bowl of water before planting in fertile, well-draining soil, 2 inches apart. Keep soil moist, but not wet, and keep the garden bed free of weeds. If you notice signs of disease, remove infected plants immediately. Harvest wasabi when rhizomes are 4 to 6 inches long. Grate what you need and store the rest in the refrigerator in a glass jar.
Wasabi is known to gardeners as one of the most difficult plants to grow. It grows on its own in rocky riverbeds in Japan, but gardeners are often unsuccessful in attempting to grow it in their gardens.
One of the reasons wasabi is so difficult to cultivate is because it needs a constant water source. In nature, water flows over wasabi, and it’s difficult to replicate this process in gardens.
It can also be difficult to find wasabi seeds or cuttings to grow from. If you do, you have to care for the plant meticulously, ensuring it doesn’t get exposed to too much humidity or nutrients. Everything needs to be just right for wasabi to grow successfully, so gardeners must be serious about the plant to have success in growing wasabi.
Wasabi grows best in warm climates with humidity. However, excessive humidity can kill off wasabi plants quickly. A wet and wooded area is one of the best places for wasabi to grow, as the natural moisture in the air usually creates the best conditions. The Pacific Northwest area of the USA is usually the most successful for growing wasabi.
Unlike many other plants, wasabi needs a lot of shade. Find an area of your garden that’s shaded under a tree or place a canopy above its garden bed.
Wasabi soil should be tilled about 10 inches deep with 10 inches of fertilizer mixed in. Test the pH and add the necessary alkaline or acidic nutrients to bring the pH level between 6.0 and 7.0. Soil should also drain quickly after water is applied, but needs to remain moist. Planting wasabi near a constant water source, like a stream in your garden, will help keep it watered.
After you buy wasabi seeds, place them in a bowl of water overnight to help jump-start germination. You should plant wasabi seeds in the late fall, as they need cool winter soil to establish strong roots. Wasabi will usually sprout in February and flower in March or April.
Plant wasabi seeds about 2 inches apart by pressing them into well-watered soil. Cover with a thin layer of soil.
You may choose to add some fertilizer to your seeds at this time if your soil level doesn’t contain the right amount of phosphorus (between 0.06 and 2.2 ppm) or potassium (between 2.0 and 3.0 ppm) levels. Your water supply may add enough of these nutrients naturally, so check your levels a few hours after planting and add fertilizer, if necessary.
Wasabi needs a constant water supply, but you must ensure that you don’t saturate the plants or soil. A steady water supply that keeps the soil moist, but not wet, is vital to the success of your wasabi plant growth.
A slow-release fertilizer for wasabi can be applied every 3 to 4 months, but only if necessary for your soil. If your wasabi nutrient levels become out of normal range, the wasabi plants may die off quickly or halt growth.
Keep your wasabi beds free of weeds, which can compete with your plants for nutrients and water. Keeping them weed-free will also help prevent pests from infesting the area to feed on the dead vegetation.
Since wasabi needs constant watering, it is more prone to diseases that occur in watery areas, like mold or root fungus. It’s particularly important to keep wasabi in cool temperatures in a shaded area, since warmed soil combined with excessive water will cause bacteria to form. This can lead to a rotted root system.
You may notice your wasabi leaves turning dark in color and wilted. Some diseases, like black leg, cause circular spots on leaves and wilting. If you find that your wasabi plants are affected by disease, dig up the infected plants as soon as possible to prevent further spreading.
You can prevent disease from the start by providing optimal growing conditions and taking care not to over-propagate your wasabi to encourage its strength.
The best way to grow new wasabi plants is by propagating them from your successfully established plants. This can help prevent disease from infected seeds you purchase elsewhere.
To propagate wasabi, you will focus on the plantlets, or the offshoots of wasabi plants. To be ready for propagation, plantlets should be at least 1 ½ inches tall, healthy without signs of disease, dark green in color, and have at least 4 or 5 leaves.
You can pull or cut each viable plantlet from the plant stem and replant them as you would a wasabi seedling. Plant them at least 2 inches apart into a fertile, well-draining soil mixed with peat moss, vermiculite, and perlite.
MrChipGardener provides a video that demonstrates how to propagate a wasabi plant:
The best time to harvest wasabi is in the spring or fall, with cooler temperatures. Your wasabi plants typically need about two full years to be ready for the first harvest, when the rhizome, or the underground vegetation, reaches about 4 to 6 inches in length. You can pull up one plant to check its length and determine whether your plants are ready for harvest.
Once you pull up a plant from the ground, you can remove the plantlets for replanting. Wash off dirt from the rhizome and use a grater to grate what you need.
To store, you can dry and ground the remaining rhizome, or place it in the refrigerator for up to 30 days in a covered glass jar.