Though many publishers, booksellers, and printers benefited from the explosion of adult coloring book sales in 2015, perhaps no company gained more than Laurence King Publishing, the original publisher of Johanna Basford’s coloring books. The U.K.-based publisher enjoyed more than a 300% increase in revenue last year over 2014, company founder Laurence King said in an interview at PW’s office last month. The increase was led by sales of Basford’s first two titles, Secret Garden and Enchanted Forest, which sold about 15 million copies worldwide through 2015.

LKP published Secret Garden in 2013 after the publisher’s editorial director, Jo Lightfoot, noticed her work in the graphic arts magazine Creative Review and thought to herself, “This would make a nice coloring book.” LKP’s interest in Basford stemmed from its history of publishing what King called “visually exciting” books.

The company entered the activity-book market in 2009 with the release of the children’s book My Wonderful World of Fashion, which sold about 300,000 copies. A year later it published what King considers LKP’s first adult coloring book, The Sneaker Coloring Book, which sold about 60,000 copies and, King said, attracted “a cool, cult, hip-hop, urban following.” The release of Secret Garden met with good early sales, many of which, the LKP staff noticed, were made by adults. This spurred the publisher to mount a publicity campaign to bring attention to the coloring book category, which was starting to build sales momentum in France. When the category began to take off in early 2015, LKP had just released Enchanted Forest. “Things went ballistic,” King recalled. “We went from shipping 20,000 copies a week to 300,000.”

Demand soared—even in the U.S., where LKP titles are distributed by Chronicle Books—and King said that keeping up “dominated my days. I’ve never seen anything like it.” The U.S. generally accounts for about one-third of LKP’s sales, but in 2015 America generated about half of all revenue. “When America hits, it hits big,” King said.

He said before sales of adult coloring books exploded, revenue for LKP, which celebrates its 25th anniversary this year, had been growing about 15% annually. He expects things to settle down this year, which will give him and the LKP staff time to think about the best way to use the infusion of capital the company received from coloring book sales. LKP will release about 110 new titles in 2016, an increase of about 25 over 2015. King said he will probably up that count much more in 2017 and 2018. As much as coloring books provided a boom to the company, King said that dealing with the issues that surrounded the frenzy forced him to delay some projects that had been on the drawing board.

King plans to expand LKP’s fashion, gift, and art book lists, adding some books in each category that appeal more to younger audiences. An expansion of the children’s list is also in the works, with 20 titles set for release this year, including Vincent’s Starry Night and Other Stories: A Children’s History of Art by art historian Michael Bird, with illustrations by Kate Evans. King sees it as a great introduction to art for tweens and young adults. LKP has done well selling books to the education market, which typically accounts for about 35% of LKP’s revenue, and King would like to expand LKP’s offerings there as well. His strategy is to build relationships with readers early, so LKP can provide them with books “from the cradle to the grave.”

Since LKP’s sales and distribution are handled by third parties (Thames & Hudson distributes LKP in the U.K.), the company, which has a staff of around 40, added only a few employees in 2015 to handle the extra business. King does hope to add one or two employees in the U.S. office, which now consists only of Debra Matsumoto, U.S. marketing manager. Any additions in 2016 would likely be on the marketing side, but King said at some point he would like to add a U.S.-based editor.

With Penguin now publishing Basford, King is eyeing ways to move the adult coloring trend forward. “I don’t want to pile on to what is being published now,” he said. Among the titles he is excited about is Matthew Williamson: Fashion, Print, and Coloring, which shows the various stages of the fashion design process—from a mood board to a coloring page, to finished samples in couture clothing. The Toolshed Coloring Book by Lee Phillips is what King calls “a man coloring book” and lets readers color different tools found in the author’s deceased grandfather’s shed. And to take advantage of Britain’s interest in maps, in October LKP will release The Great British Coloring Map, from the Ordnance Survey, the national mapping agency for Great Britain. “We helped create the coloring book trend,” King said, “I’d like to lead it somewhere new.”