Wasabi Fans, We prefer to plant wasabi in the early autumn. Though Spring is traditionally the universal crop-planting season to prepare for the summer sunshine, wasabi grows fastest during the transition seasons; Spring and Autumn. Thus, planting to prepare for these seasons is important to establish the plant starts. Think of wasabi as garlic; plant it in the autumn so it establishes and is ready to take maximum advantage of early Spring. We do this at Frog Eyes Wasabi Farm and recommend it for the home garden as well. This timing takes advantage of the cloudy day of Spring which establishes the plants so they flower in late Winter/early Spring.
Depending on your location, your springtime may be too hot or dry for wasabi to really take root. As long as your winter doesn't freeze too hard or long (below 25dF or for more than 48 hours duration), I think Autumn is the time for you. This photo was taken approximately two months after planting in Sept. 2014. This was the first ice storm of the season. Look closely and the leaves are very shiny from the freezing rain. The plants above are the same ones and indeed survived the winter (though not the neglect and heat of the summer).
Indoor is ok, just make sure to NOT put it under a light. Remember, we as an agriculturally-centered society, we think of food products being grown in open fields with lots of summer sunshine. Though wasabi is indeed a food crop in that sense, it does not thrive in sunshine. I can't stress this enough. It is the primary reason wasabi doesn't flourish in gardens or long enough to become a food crop in your backyard. This plant wants shade. All year. 365 days per year.
Potted wasabi plant (shown outside, but taken inside for the winter).
Photo below: Daio Wasabi Farm in Japan. Photo courtesy: http://www.thesoupspoon.com/all-about-real-fresh-wasabi/
Err on the side of shade. not sun. These leaves shown with very diffused winter light on February 20 2015 in the shade on a cloudy day (on the left) and the same plant in the sun on Feb. 28 2015. Keep in mind that this is the sunshine at 46 degrees north in winter sun. Though the leaves recovered, it shows that wasabi really prefers shade. This is what makes wasabi a great garden crop, it'll grow where other vegetables don't thrive. Plant it under the boxwood on the east side of the house, next to the moss, not on the south side of the tomatoes! Remember, we have preparation and planting information on our webpage: http://www.thewasabistore.com/wasabi-plant-starts/ And, plant starts can be purchased here: http://www.thewasabistore.com/shop/wasabi-plantlet