Katakuri, or dogtooth violets, grow in abundance during spring in numerous parts of Japan. If you're looking for one of the largest displays of these flowers in all of the country, Totsushozan in the Asahikawa area of Hokkaido is worth a visit.
The flowers are easily affected by the weather conditions, and when the temperatures are cold the flowers droop quite a bit. The best time to visit is between 11 am and 3 pm when the temperature rises and the flowers do, too!
Last year's peak for the flowers in bloom was right around the end of April, so tentatively assume it should be similar this year, too.