“Peace, Love & Misunderstanding” is a forgiving little trifle, an open-air feast of Woodstock Generation cliches. But how much you forgive this depends on your tolerance for tie-dye, Jane Fonda, senior citizens who never outgrew their ’60s idealism, and the Grateful Dead.

Fonda lends a little ’60s sass to a timeworn tale of daughters testing and judging their mothers. Whatever other thin virtues the movie can claim, she alone is worth the price of admission.

Fonda is Grace, the mother to that “patron saint of the uptight,” New York attorney Diane (Catherine Keener). Mother and daughter have been estranged for 20 years. They have issues — and not just wildly divergent lifestyles and politics.

Whatever their differences, Diane flees to Grace’s farm with her college-age daughter (Elizabeth Olsen) and teenage son (Nat Wolff) when Diane’s husband (Kyle MacLachlan) demands a divorce.

Granny Grace lives in Woodstock, N.Y. She tells the story that Diane — whom she named Diana — was born during the Jimi Hendrix set at the famous concert there, 43 years ago. Grace, in every way you can imagine, never left Woodstock.

Granny still smokes pot. She still grows it. Heck, she’ll teach the kids all about cannabis.

“It’s OK to toke a little hay,” she lectures. “But nothing in needles! Nothing up the nose!”

There’s the weekly Saturday morning protest, the Full Moon celebration of fertility that all the local women come to (Rosanna Arquette among them). And the painting — Granny likes sleeping with the guy who models for the nude portraits she paints.

Diane is still embarrassed by her mom’s refusal to grow up. But her daughter, Zoe, is just as ashamed that Mom is all on board the divorce train, and that she slips into an easy flirtation with local singer/ furniture maker Jude (Jeffrey Dean Morgan).

Idealistic Zoe tests her anti-violence/ vegan beliefs when she’s attracted to the town’s hunky butcher (Chace Crawford). Socially inept Jake (Wolff), who videotapes everything, gets seduction advice from Granny when he takes a shine to a local hippie teen.

Director Bruce Beresford (“Tender Mercies,” “Driving Miss Daisy”) follows his artist-escapes-from-communist-China biopic, “Mao’s Last Dancer,” with a romance that rarely aspires to be more than cute. Keener, cast against her Earth Child vibe, struggles to suggest a woman who would be in the least bit conflicted by being drawn to hipster Morgan and the skinny dipping/ free love lifestyle that her mother espoused. Morgan, in his second shot at a Woodstock movie (“Taking Woodstock”), has an easygoing charm here. And he and Keener share one magical moment — a duet on a song that he plays in concert, that she knows from her childhood.

The kids are likable, with Olsen (“Martha Marcy May Marlene”) meeting her beguiling match in hunk-du-jour Crawford (“What to Expect When You’re Expecting”).

But it is Fonda, serving up the ’60s, who is reason enough to check this one out. “I’m positively oracular,” she bubbles. Her Grace is an open invitation to “Peace, Love & Misunderstanding.” Everybody’s welcome, even those Fonda peers who never got over their lifelong Fonda hate. As Grace would put it, “Exclusion is an unnecessary violence, don’t you think?”