After reading Dr. Lynette Morgan’s articles on growing wasabi, I now want to give it a try. My question is, what is the recommended color temperature for growing wasabi? Also, are there different varieties of wasabi? Or is wasabi just wasabi? Thank you!
There are more than 20 varieties of wasabi known in its native habitat, Japan, where cultivars are often region specific. In the United States, the main cultivars grown commercially are Daruma and Mazuma, and often these are the only ones available. The recommended cultivar for hydroponic production is Daruma, as it can better tolerate a major disease of wasabi called black leg (Phoma wasabiae), which is difficult to control and can result in large losses of yield and quality. Daruma develops a thick, green stem and has an upright growth habit. Mazuma can be grown hydroponically, but it is reported to have a more horizontal growth habit, poorer market quality, and greater susceptibility to diseases such as soft rot and black leg.
A wasabi crop can be started from small plantlets, from tissue-culture plantlets or from seed. Seed germination can be difficult as certain dormancy requirements must be met before germination can occur, plus seeds can be hard to obtain. The most preferred way to start a crop is buying small plantlets, which are offshoots produced around the crown of the mother plant. Generally these plantlets transplant well into hydroponic systems.
Wasabi is an excellent crop to grow indoors under artificial light. This is because it has specific environmental requirements and because light can be manipulated to boost growth and yields. Wasabi is a highly vegetative crop that grows many large leaves over a 12-18-month production period. Although the plants often flower, blooms are not the harvestable portions of the plants. It is the long, thick stem of the plant that is harvested for use as fresh wasabi, and the rate of development of this stem depends on how fast leaves are formed and how rapidly they mature. For this reason, a color temperature that promotes strong, compact and rapid vegetative growth is recommended. In other words, more of the blue wavelengths are beneficial in this case. Start with a color temperature of 4,000°K, or even 5,000-5,500°K, which boosts the blue portion of the spectrum. This temperature better simulates the natural environment of wasabi, which traditionally grows in heavily shaded conditions in Japan under trees on river banks.
Another factor to consider is that light intensity, particularly for young seedlings or transplants, will need to be considerably lower than that required by many indoor crops such as tomatoes. The intensity should be more like that supplied to young lettuce plants or shade-loving houseplants. Wasabi also requires cool conditions, so using LEDs will assist in preventing heat buildup and leaf burn. Artificial lighting also allows day length to be extended, boosting growth even further. A day length of more than 20 hours of low-intensity light will allow maximum photosynthesis to occur, without the issues of attempting to increase growth via higher light intensity, which wasabi cannot tolerate.
The correct lighting intensity, combined with cooler temperatures, optimal humidity levels (fogging or misting may be beneficial), a well-designed hydroponic system such as a water culture or gravel system, and even the use of CO2 enrichment should provide you with a strong, healthy harvest of this exotic herb.