The late author-illustrator Shel Silverstein (1930–1999) knew exactly how he wanted his children’s books to look, right down to the color and weight of the paper and the size of the type. In that same aesthetic vein he stipulated that his works not be published in paperback editions. Few people know Silverstein’s design preferences better than Antonia Markiet, senior executive editor at HarperCollins Children’s Books, who first worked with him in the mid-1970s. Markiet has been chief caretaker of the Silverstein catalogue since 2001 – a role in which, she says, she aims to keep Silverstein’s titles “fresh and available,” and anniversary editions are a way to do just that. “They are wonderful opportunities to put backlist titles into the public’s eye,” she says.

This year, HarperCollins is marking numerous Silverstein milestones as picture books.The Giving Tree (which has sold more than 10 million copies), Don’t Bump the Glump!, Who Wants a Cheap Rhinoceros? and A Giraffe and a Half all celebrate 50 years in print, and poetry collection Where the Sidewalk Ends (which also has sales of 10 million copies) turns 40. In February, the publisher kicked off a six-figure, year-long marketing campaign to observe these significant book birthdays. Commemorative editions of each of the five titles were released on February 18, as was the first-ever digital version of The Giving Tree, marking the only time a Silverstein book has appeared in a format other than hardcover.

According to Markiet, the challenge of any Silverstein book anniversary is “what do you do to the books that is in line with what Shel had done or might have liked? Sometimes all you can do is add a sticker.” As examples of more significant tweaks, she cites the 50th-anniversary edition of The Giving Tree, which features a green foil jacket, and the 30th-anniversary edition of Where the Sidewalk Ends, which included 12 additional pages of previously unpublished poems.

But any planning for new projects begins by speaking with Silverstein’s family members, who maintain an archive of his original art and papers in Chicago. “We talk to the family and see what they might consider,” Markiet says. “And it’s great that they do consider what we suggest. For the recent editions of A Giraffe and a Half and Lafcadio, the Lion Who Shot Back (which turned 50 last year), Markiet says she went back to the vintage jackets using the type and color from 50 years ago. “We looked at our archives and the family archives to see if the paper was a different color and it was cream more than blue-white,” she said. The vintage jackets will be available for a limited time, in tandem with the more familiar, long-running, black-and-white versions. “It’s nice to offer both and let people decide; they can buy a copy for nostalgia,” Markiet notes.

Though jazzed-up jackets and stickers bring new attention, Markiet believes it’s what’s inside Silverstein’s books that account for their longevity. “Shel was a perfectionist in the better sense of the word,” Markiet says. “No detail was too small. He was a master of rhythm, direct in his ideas, and he followed his own drummer.” She recalls how Silverstein would work from the vision in his head, putting several versions of spreads on Bristol board (a type of uncoated paperboard) and moving them around on a wall. “He read the poems out loud, in a variety of ways, working on the rhythm of language and word choice, whether to use ‘ing’ or ‘in’’ ” she says. “His irreverence, his particular sense of humor and his respect for the intelligence of the reader” help make his books ones that “kids want to read 50 or 60 times,” she adds. “He knew instinctively what worked, and it translates into what kids respond to.”

Shouldering the responsibility for Silverstein’s backlist is “humbling and terrifying,” Markiet says. “There is certainly gratification, and being able to bring 50-year-old classics to new generations of kids spoils you a bit,” she adds. “Shel was one of the best that ever was. Kids still love his work and scream with laughter – and so do people my age!”