For more than a century, Frances Hodgson Burnett’s “The Secret Garden,” first published in 1911, has endured. It remains one of the great classics of children’s literature, a book that deftly combines the dreams and nightmares of childhood. Its balance of dark and light, death and rebirth is still powerfully moving in its rare harmony. Mark Mundan’s adaptation, which STX Films will release on-demand Friday, struggles to burrow into the interiors of its characters. It’s sluggish at times and too withdrawn for such a vibrant tale. But it stays nevertheless in tune with the spirit of Burnett’s book, and by the time it reaches its late crescendo, this “Secret Garden” blooms nevertheless. “The Secret Garden” has been adapted many times before but only once as a major movie, in 1993. Agnieszka Holland’s version, a superbly crafted family film, remains a classic in its own right. Produced by Francis Ford Coppola, shot by Roger Deakins and featuring Maggie Smith as the housekeeper, Holland’s “Secret Garden” (currently streaming on HBO Max) is tough to top. Mundan’s film, scripted by Jack Thorne, softens some of the edges of its central character, Mary Lennox (Dixie Egerickx). The first line of Burnett’s book refers to the orphaned Mary, whose parents never wanted her, as “the most disagreeable child ever seen.” After a brief prologue in India, where Mary’s parents die of cholera, she arrives at the gloomy and gothic Misselthwaite Manor on the Yorkshire Moors. There she’s been taken in by her uncle Archibald Craven (Colin Firth) who, himself, is grieving the loss of his wife. Mary finds herself generally locked in her room, and only gradually does she encounter Archibald or his largely bedridden son Colin (Edan Hayhurst). Her first and for a while only friend is Dixon (Amir Wilson), the gardener’s son. Together, they discover, behind stone walls and ivy, the hidden, dreamlike garden that will propel and reflect their collective healing. The best that can be said about Mundan’s “Secret Garden” is that it doesn’t try to gin up the story or gloss over its themes. This is a pleasingly patient film that honestly tackles grief, death and rejuvenation without sentimentality. Given today’s average wide-release children’s films, that makes “The Secret Garden” a verdant oasis. “The Secret Garden,” a STX Entertainment release, is rated PG by the Motion Picture Association of America for thematic elements and some mild peril. Running time: 102 minutes. Two and a half stars out of four.