http://www.amazon.com/Lavender-Green-Magic-Books-5/dp/0765353016/ref=cm_cr_pr_product_top Set in the 1970's
From Amazon:
" A mysterious maze
Eleven-year-old Holly Wade and her twin siblings, Judy and Crockett, are sent to live with their grandparents in the small town of Dimsdale, Massachusetts when their father is declared missing in action in Vietnam. Dimsdale is nothing like Boston; there are only two other African-American children in the entire school. Even worse, Grandpa and Grandma Wade live in an old junkyard! While exploring one day, Holly, Judy, and Crockett wander into an overgrown hedge maze--and find themselves transported back in time to Dimsdale's past. Can they right an ancient wrong and free the town of Dimsdale from a witch's curse?"
"Yet what I particularly liked about the book were the characters. Holly makes for a very interesting heroine since you spend half the book wishing she'd stop being such a jerk. When she allies herself with a particularly nasty witch of the past, the reader has the painful task of watching as she makes a bad situation for herself even worse."