As the youngest entrant to design a garden for the Malvern Spring Gardening Show 2008, he was thrust into the spotlight with interest from the BBC and big-name designers.
But this was no flash in the pan. In the past seven months the teenager has clocked up silver medals at the London Plant & Design Show and RHS Hampton Court Palace Flower Show, and a silver-gilt at the Malvern Spring Gardening Show 2009.
Now 16, the plant-mad schoolboy has just received his GCSE results and is hoping to take his garden design a step further with an entry at the RHS Chelsea Flower Show next May.
"My friends think it's mad I'm doing all this," he laughs. "None of them are into gardening. But it would be nice to inspire other young people to get into horticulture."
Following Dunckley around his home and garden in West Sussex, his enthusiasm for plants is infectious as he points out some of his favourites as well as the remnants of his latest design, A Desert's Delight, which he created at Hampton Court in July.
At the bottom of the garden is a small nursery - including a polytunnel and plant benches - that he built from scratch with his father, Robert.
There are plants at various stages of growth stacked everywhere. Carefully lined up and labelled, this is the start of a business Dunckley is nurturing to see him through his studies.
Although still too young to sign up for the three-year Kew Diploma, he is determined to gain as much experience as possible to be accepted for the prestigious qualification at the earliest opportunity.
"I think being in the business from such a young age will help me as I get older, particularly in this financial climate," explains Dunckley. "I think it is better to start a business in bad times because it helps you (keep control on spending) in good times."
Combining a passion for plants with a strong entrepreneurial spirit appears to be paying off for Dunckley.
His small enterprise is already making a profit as he buys cuttings and young plants from Delamore, before growing them on and selling to local nurseries and designers.
But rather than spending his takings on DVDs, clothes and going out, Dunckley is ploughing all the cash back into the business and has plans to expand to a larger site over the next two years.
"Being in business this year, I have noticed what has sold well," he says. "Herbaceous perennials have sold really well, better than any bedding. People do have less time and are starting to realise which plants will require less looking after.
"I am learning from trial and error, though - I was selling pansies in 9cm pots and hardly sold any. But then I found that people would rather buy a tray for £3 than six individual pots for 50p each."
Having developed an interest in gardening at around the age of six, Dunckley embraces a circular approach to his designs - from growing the plants to capturing personal experiences in his gardens and helping build them.
His very first garden - Ornamental Hurst at Malvern 2008 - drew on his interest in history, as well as incorporating the name of his school, Hurstpierpoint College. A year later, he dedicated a garden to his grandmother Margaret, who had worked in a florist's shop as a young girl and had a passion for gardening before the onset of dementia.
"I am pretty much self-taught," explains Dunckley. "But the biggest thing is about not being afraid to get out and get your hands dirty. I think designers should be involved with the build."
One of Dunckley's mentors has been his friend and fellow horticulturist Clive Parker, who is the retail manager at Birchfield Nursery in West Sussex.
Dunckley's business smarts mean he is already skilled at using his contacts in the industry, and he sold some of his show plants to Parker after exhibiting. He also shared deliveries with fellow Malvern designer Alex Bell, who lives nearby.
Developing a strong relationship with RHS shows organiser Bob Sweet, as well as making contacts at Bradstone and gazebo firm Breeze House, allowed Dunckley to raise sponsorship for Hampton Court - including £35,000 from the RHS.
Dunckley's ideas for designs, plants and potential sponsors are constantly galloping through his mind and he seems to have an unbridled energy for all things garden.
With the deadline for his Chelsea entry looming, Dunckley reflects on the 2009 show. "Ulf Nordfjell's garden was absolutely beautiful and very simplistic," he says. The modern style, with strong design elements, is something Dunckley hopes to develop in his own garden.
"I'm creating a flat-roof structure filled with lights, modelled on one I saw in Spain, and the whole feel is about al fresco dining and simple lines," he reveals.
If Dunckley's ambition is anything to go by, this won't be the only Chelsea garden he will be planning over the coming years.
2008: Ornamental Hurst garden at Malvern Spring Gardening Show
2008: Runner-up in Chris Beardshaw Mentoring Scholarship
2009: Balcony garden at London Plant & Design Show
2009: Not Any Garden, My Grandma's garden at Malvern Spring Gardening Show
2009: A Desert's Delight garden at RHS Hampton Court Flower Palace Show