Mark your calendars now for the 20th Annual Spring Garden Tour, hosted by Soroptimist International of the Sierra Foothills (SISF), scheduled for Saturday and Sunday, May 18 and 19. This event is a self-guided tour of six privately-owned gardens in Grass Valley, Nevada City and Penn Valley.  Gardens are open from 10 a.m. to 4 p.m. and the cost is $20 in advance or $25 at the garden gate. Tickets go on sale in early March.  Wear comfortable shoes, bring a hat, and don’t forget your camera on this four-to-five hour excursion. The Garden Tour is the primary fundraiser of Soroptimist …