Dr. Keith Hammett: Shaping Dahlia Genetics and Breeding for the Future

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Renowned as one of the world’s foremost plant breeders, Dr. Keith Hammett has spent decades transforming the world of dahlias, combining scientific rigor with artistic creativity. His work has influenced both home gardeners and professional breeders, leaving an indelible mark on the horticultural landscape. Dr. Hammett’s passion for innovation, paired with his respect for traditional methods, makes his breeding philosophy as fascinating as the flowers he creates.

Dr. Hammett’s journey into plant breeding began in his teenage years in England, where a chance mentorship with a local champion dahlia grower ignited a lifelong passion. By the age of 15, he was already excelling in competitive dahlia exhibitions, gaining both practical experience and a foundational understanding of plant physiology. This early exposure laid the groundwork for a career that would blend hands-on gardening expertise with cutting-edge scientific research.

After earning a Ph.D. in botany, Dr. Hammett initially worked as a plant pathologist. However, his growing fascination with plant breeding soon took precedence. A move to New Zealand provided the perfect environment for his ambitions, enabling him to focus on developing new cultivars of dahlias and other ornamental plants. Over the years, he has become a leading figure in the dahlia world, celebrated for his contributions to breeding, exhibiting, and mentoring the next generation of enthusiasts.

One of Dr. Hammett’s most iconic contributions to the world of dahlias is the development of the 'Mystic' series. Known for their dark foliage and vibrant, single blooms, these cultivars introduced a bold new aesthetic to dahlia enthusiasts. Dr. Hammett recounts how his trips to Mexico—where he observed wild dahlias in their natural habitat—spurred his interest in foliage diversity. Inspired by the finely divided leaves and varied colors he saw in the wild, he set out to create dahlias that were as visually striking out of bloom as they were in full flower.

The 'Mystic' series was a triumph of this vision. Each variety features dark, nearly black foliage, which contrasts dramatically with its brightly colored blooms. Cultivars such as 'Knockout,' marketed as 'Mystic Illusion' in some regions, stand out for their golden-yellow flowers with a deep black disc. Dr. Hammett considers this variety a personal favorite, describing it as “not an illusion, but truly a knockout.”

Dr. Hammett’s innovative work with dark foliage broke the mold of traditional dahlia breeding, which had largely focused on bloom shapes and colors. By emphasizing foliage, he expanded the horticultural palette available to breeders and gardeners alike. The success of the 'Mystic' series also demonstrated the commercial viability of breeding goals that diverged from conventional exhibition standards, a theme that continues to inspire breeders worldwide.

For Dr. Hammett, breeding is as much about creativity as it is about scientific precision. His approach begins with a clear goal, whether it’s developing new forms, enhancing specific traits, or addressing challenges like virus management. “The first essential in any breeding program is to have a goal,” he explains. This guiding principle has allowed him to navigate the complexities of dahlia genetics while staying focused on achieving meaningful outcomes.

One of Dr. Hammett’s most innovative tools is the foliage-color scale he devised to guide his work with dark-leaved dahlias. The scale ranges from 1 (green foliage) to 5 (nearly black foliage), with a more recent addition of level 6 to denote leaves that are dark on both surfaces. This systematic approach has enabled him to select and refine plants over multiple generations, gradually intensifying the desired coloration. By combining meticulous selection with bold experimentation, he has pushed the boundaries of what’s possible in dahlia breeding.

While Dr. Hammett is celebrated for his creative vision, his approach to breeding is deeply rooted in scientific principles. One of his most significant challenges has been addressing the prevalence of viruses in dahlia populations. Rather than attempting to eliminate viruses entirely—a process he considers impractical—Dr. Hammett has focused on developing cultivars that are virus-tolerant.

He explains, “Most cultivars have a finite lifespan with or without the virus. It’s not about resistance—it’s about tolerance.” Virus-tolerant plants can thrive despite the presence of pathogens, ensuring their longevity and performance in gardens. Cultivars like 'Bishop of Llandaff,' which has endured for nearly a century, exemplify this trait. Dr. Hammett sees this as a testament to the plant’s ability to coexist with viral infections while maintaining its vigor and beauty.

To achieve virus tolerance, Dr. Hammett has often looked to older, time-tested cultivars. “The plants that have stood the test of time are often the best starting points,” he notes. By incorporating these resilient genetics into his breeding programs, he ensures that new varieties inherit the durability needed to thrive in diverse environments.

This philosophy reflects a broader balance in Dr. Hammett’s work: combining the best of tradition with forward-thinking innovation. His use of line breeding—a methodical process of selecting and crossing plants over multiple generations—has allowed him to achieve specific goals while maintaining genetic stability. At the same time, he has not shied away from exploring uncharted territory, growing large populations to uncover novel traits and break free from conventional breeding limitations.

Dr. Hammett’s breeding efforts are as much about shaping the future as they are about celebrating the past. His work with the 'Mystic' series and virus-tolerant dahlias reflects a commitment to pushing boundaries while preserving the heritage of this beloved plant. By blending traditional techniques with bold experimentation, he has created a roadmap for the next generation of breeders.

As the dahlia’s popularity continues to grow, Dr. Hammett’s legacy serves as both an inspiration and a challenge: to see beyond the flower’s surface and explore the infinite possibilities within its genetics. Whether developing cultivars that dazzle in gardens or mentoring new breeders, Dr. Hammett embodies the spirit of discovery that keeps horticulture vibrant and ever-evolving.

Watch Dr. Hammett as he discusses his dark-foliage breeding work–and shows off many of his dahlias–in this video .

Read Dr. Hammett's article titled "A Plant Breeder's Perspective" from the New Zealand Garden Journal (2009).

Learn more about Dr. Keith Hammett and his amazing work on his website and follow him on Instagram.

This article is based on an interview with Dr. Keith Hammett on the Quince Flowers Podcast which first aired on November 19, 2021. This Australia-based podcast series is hosted by siblings Caitlyn Mason and Peter Mason, whose contributions to dahlia knowledge are gratefully acknowledged by the author.

You can listen to the entire podcast episode with Dr. Hammett, and enjoy conversations with other dahlia experts, wherever you get your podcasts . Search “Quince Flowers” and follow the Quince Flowers Podcast on Instagram .