WHEN Johanna Basford was a child, her grandparents lived in a house within the grounds of Brodick Castle on Arran. Her grandfather John was the head gardener for the estate and her grandmother Joan an artist with a lifelong passion for horticulture.

After the couple passed away, Aberdeenshire-based illustrator Basford inherited her grandmother's collection of botanical reference books which contained a series of meticulously coloured-in black and white drawings.

"Every time my gran found a flower that she hadn't encountered before, she would colour in the picture in her book," explains Basford. "Whether it was a little wildflower in Scotland or a rare orchid that she came across in a far-flung place, she would take these little books and colour them in."

It provided the inspiration for Basford's latest book, World of Flowers, published on Thursday. For those unfamiliar with her work, the 35-year-old is a pioneer of the adult colouring book trend.

The self-dubbed "ink evangelist" published her first title, Secret Garden, in 2013. She has since gone on to publish six more, including Enchanted Forest, Magical Jungle and Lost Ocean, igniting a new genre and selling more than 21 million copies worldwide to date.

Basford gives a hearty laugh when asked whether she imagined this level of success and longevity starting out. "No," she says. "Secret Garden was a passion project that I thought my mum was going to have to buy a lot of copies of to help me save face."

She admits that 21 million book sales is a figure simply too colossal to wrap her head around. "I remember getting excited about 100,000 and then it being almost 200,000, but after that the numbers get so abstract that you can't comprehend them. We are in more than 40 countries now."

World of Flowers, says Basford, is an idea that has been percolating in the back of her mind for some years. "It is everything I love," she says. "It is almost the book I wanted to create with Secret Garden but was a little bit too scared to."

Flicking through the pages, the intricate black and white illustrations are every bit the floral adventure that colouring book fans will relish, yet upon closer inspection eagle-eyed plant lovers may notice a quirky twist.

"I tell people that these are 'inky hybrids', which means I take a little bit of inspiration from real blooms – it could be orchids, fuchsias, all different flowers," she says. "I maybe take a petal from one flower, the leaf from another and then combine them to make brand new flowers.

"The reason for that is quite sneaky. It means there are no right or wrong colours. When people are colouring, you don't want to get stressed out thinking: 'Is my daffodil the correct shade of yellow?' My flowers, although they might have a hint of something real, are all just made up. So, you can use any colour you want."

Does Basford have a favourite flower among her latest collection? "There is one called a Corpse Flower," she says, referring to the Amorphophallus titanum, a lofty flowering plant famed for its pungent smelling bloom.

"I felt that poor blossom needed a bit of love so there is a page inspired by that. It is quite ornate. You get scented gel pens and I love the idea that it could be coloured in with something that smells really nice." Rather than a whiff of rancid, rotting flesh? "Exactly," she laughs. "That page tickles me."

With flora and fauna such a strong theme running throughout her work, it is little surprise that Basford had a rural upbringing. Her parents own a fish farm in Auchnagatt, north of Aberdeen, and she fondly recalls a childhood spent among nature.

Basford and her sister would build dens or paddle in the burn looking for tadpoles. "Being outdoors and having that sense of freedom was so pivotal to me," she says. "It was definitely a foundation in what has made me who I am, my sense of creativity and appreciation for nature."

These days she lives close to Ellon – a few miles down the road from her childhood home – with her husband James Watt, the co-founder of Scottish craft beer company BrewDog, their two daughters 18-month-old Mia, and Evie, four, and a Labrador called Simcoe.

Her joy is palpable when Basford talks about getting her children outside and learning about the natural world. "Bless them, they both love it," she says. "They often go up to the fish farm and spend a day with my mum and dad.

"They will come back absolutely filthy and knackered but delighted. Usually with bags and baskets full of things they have found such as twigs, stones, conkers and seed pods. We had a dead bumble bee in a jam jar for a long time – they found it dead, they didn't catch it.

"I try to really nurture that sense of wonder because I think it is brilliant – anything I can do that stops them asking for the iPad is a total bonus."

Television presenter Kirstie Allsopp recently admitted she smashed her children's iPads after they broke her screen-time rules. I'm curious how Basford – who speaks about championing the pen and pencil over the pixel – feels about ever-encroaching technology within our lives?

"I'm not totally against the technology," she says. "I think they are growing up in a world where they need to be able to use it and it is important that they can, but it shouldn't replace all the things that are going to make them well-rounded humans and give them real life experiences.

"If the difference is watching a YouTube video about migrating birds or being outside and seeing a V of geese fly over. I want them to do the latter. It builds memories and that is important.

"We recently saw a murmuration of starlings. I had seen it on the TV and showed Evie a YouTube video, but then it actually happened near our house.

"Being in a field outside, seeing and hearing that, feeling the crunchy ground underneath your feet and being out in the fresh air is a memory that will be ingrained in her mind. I don't think anything on a screen or digital can ever replicate that."

Basford is grateful for her own experiences in that vein, not least the time spent with her paternal grandmother Joan. "She was a tremendous woman who had such a creative mind. Although my grandfather was the head gardener, my gran was a trained gardener herself.

"She was big into flower arranging and could bring back to life any plant. I felt in a way she got overshadowed by my grandfather sometimes because he was the head gardener and had all the prestige, but my gran was just as skilled and knowledgeable."

Her grandmother raised four children before studying art later in life. "She was very much what we would now call a stay-at-home mum," says Basford. "My grandfather was quite traditional, so he wouldn't have been helping.

"She went back to night school and put herself through art school in Glasgow. She was getting the boat over once a week from Arran to go to these classes."

Basford's verve for life is no less impressive. "I love the idea of creating these magical inky worlds for people to escape into and explore," she says. "When I had my kids, I made the decision very consciously that I would only do work that I loved and enjoyed doing.

"Every time I do a book it is because I absolutely want to do it and I've had this great idea. I can't wait to get those all those pictures down on the page and share them with people. I try to make each book a little separate adventure, so people can feel that they have been on a journey with me."

World of Flowers by Johanna Basford is published by Virgin Books on Thursday, priced £12.99