Wasabi is a perennial, semi-aquatic herb native to Japan. It belongs to the Brassicaceae family of plants. Growing wasabi has been a common practice among the Japanese for thousands of years. With the Japanese cuisine gaining a lot of popularity in recent years, growing wasabi is increasingly being practised by thousands if not millions of farmers worldwide. Wasabi is an expensive plant that is highly profitable to its farmers. It is however also considered as one of the world’s most rare and capital intensive crops to grow. As such, wasabi farmers should be highly skilled and knowledgeable on wasabi farming practices.

Climate

Wasabi excels in cool and moist temperate climates. Wasabi is a semi-aquatic plant thus thrives in an aquatic habitat with low temperatures of about 12oC to 15oC. Temperatures less than 8oC hinder proper plant growth, the plant ceases to grow once temperatures fall below 5oC. Growing wasabi requires constant water temperature, well nutrient status in the water and neutral or slightly acidic pH.  Wasabi can also be grown on soil. Growing wasabi on soils requires air temperatures of about 8oC to 18oC. The soil should have a pH of 6 to 7. Wasabi can be grown on damp sites and in pots filled with water. However, the upside of growing wasabi in areas with running water is that water temperatures are near constant regardless of seasonal fluctuations in air temperature. Such conditions are the most ideal for growing wasabi.

Water grown wasabi

Caution should be taken when growing wasabi on water. Farmers should always make sure the water is clean as silty or muddy water may contain insufficient oxygen. Some silty water is however considered as a source of nutrients. The ideal water source for growing wasabi is one that has stable temperatures and high levels of oxygen. High temperatures lead to limited oxygen which negatively affects the growth of the plant. Rainfall accumulation is also important, with an even distribution desirable to stabilize the water supply and temperature.

Soil Preparation

Wasabi thrives in loose, highly organic as well as moist to wet soils with a pH of 6 to 7. It is essential that pH level are as recommended so as to prevent nutrient deficiencies and diseases. A soil test should be done prior to fertilization so as to determine the exact fertility of the soil and the necessary nutrient supplements with their specific amounts. Fertiliser has to be applied into the top 6 inches of the soil, if required. Compost on the other hand is applied 2 to 3 inches per every 100 square feet. Phosphate fertiliser should be incorporated into the soil before planting. Potash can also be applied during the same period. Nitrogen is applied in small amounts over the growing season but none is used on young seedlings that have recently been planted. The ideal area for growing wasabi is on streams or near the pond where fresh water is readily available. Wasabi can also be grown under heavily shaded areas as it is susceptible to high temperatures.

Choice of cultivar

Choice of Cultivar is an important aspect to consider when growing wasabi. There are many varieties which differ in terms of stem shape, size, colour and tolerance to temperature. The choice of the cultivar therefore depends adaptability and reliability among other factors. The variety selected has to be ideal for the climate and highly resistant to pests and diseases dominant in the farming area. Farmers should acquire adequate knowledge about various seeds before selection so as select the cultivar best suited for their environment.

Planting

The ideal planting procedure for growing wasabi is one that allows ½ inch of the plant crown to be above the surface. Depending on weather patterns, the plant should be placed under a shed so that it is at least sheltered from bad weather 75% during the day. It is recommended to plant wasabi in a 9cm pot with compost to allow the establishment of good root structure and to strengthen the plant before transplanting 4 to 5 weeks later. When planting in a pot, sand can be placed underneath to increase drainage. Growing wasabi on soil requires thorough and frequent watering. Wasabi should be planted 12 inches apart. It grows up to 8 to 18 inches high. Note that wilted leaves can be a sign of inadequate root development therefore if it appears, humidity should first be increased; if the problem persists remove and replant in a new area. It takes about 2 years before the wasabi rhizome matures to full size and flavour.

Weed Control

Weed control is very important in growing wasabi. Weeds can be controlled through mechanical and chemical means using registered herbicides. Cultivation should be shallow; it should not be done too close to the plant as it might cause harm. Appropriate herbicides should be used in the recommended quantities in cases of disease or pest outbreak. The area surrounding wasabi has to be kept clean and weed-free at all times. Dead leaves as well as all dead matter should be removed to prevent infestation.

Pests and Diseases

The low temperatures necessary for growing wasabi is to some extent, a form of protection form pests and diseases. Low temperatures discourage pests and diseases hence reduced incidences. However, as a member of the brassica or crucifer family, wasabi is subject to many pests and diseases that attack other crops in the same family. These include various stem root fungal and bacterial diseases. It is difficult to control such pests and diseases in running natural running water systems. Wasabi can also be attacked by predatory slugs and snails. Mulch can be applied around the perimeter of the site to control pests. None the less once established, pests and diseases are unlikely to be a challenge in a healthy plant.

Harvesting Wasabi

It takes at least 2 years for wasabi to mature to its full size and flavour, however, farmers usually leave it for up to 3 years before harvesting. Wasabi can be harvested throughout the year depending on climate and seed variety. Read more about harvesting wasabi.

Growing wasabi is challenging in areas with high as well as extremely low temperatures. The advantage however is that wasabi can be grown in containers where conditions can be controlled. Wasabi can either be grown in water or on land though it thrives in aquatic environments. When growing wasabi farmers need to take note that the environment under which the wasabi is grown has an impact on the price of the plant. Wasabi grown in water is considered more expensive and of superior quality than that grown on soil.