Sharing global lessons for how we can help our gardens grow

By Connor Ryan, Rhododendron Collections Manager

Clianthus puniceus, New Zealand Glory Pea, a New Zealand endemic nearly extinct in the wild but thriving at RBGV-Melbourne in two different color forms.

This past fall I attended the 7th Global Botanic Gardens Congress in Melbourne, Australia. This is a semi-regular meeting of botanic gardens from around the world sponsored by Botanic Gardens Conservation International. More than 500 people attended. The theme of the Congress was “Botanic Gardens as Agents of Change,” and talks and tours centered around how gardens can make a difference in plant conservation, in curbing climate change and in engaging our communities.

There were many take-aways from the Congress — countless inspiring talks and people. I want to take this opportunity to highlight a theme of the Congress that is part of the botanical garden world but is underutilized and underdeveloped: conservation horticulture. Conservation horticulture is an emerging field that may or may not intertwine with typical horticultural work of plant production, garden design and grounds maintenance. What distinguishes conservation horticulture is that underlying all work is the intent to preserve and restore rare plants. The red sand garden at Royal Botanic Gardens Victoria – Cranbourne Gardens.

Banksia spinulosa, a species endemic to eastern Australia, thriving in RBGV-Melbourne, and blooming during what is their springtime!

Araucaria laubenfelsii (left) and Araucaria muelleri (right), monkey puzzle relatives endemic to New Caledonia and growing in the collections at Royal Botanic Gardens Victoria – Melbourne Gardens.

Botanical gardens maintain plant collections for many reasons — ornamental display, scientific research, education, etc. We often consider the plants on our grounds as highly valuable for conservation purposes. They are living representatives of species under the care of expert horticulturists, after all. But what does it really mean to have collections of conservation value? And are we doing it right?

Many talks at the Congress centered around this theme. I was impressed by how the conservation horticulture teams at many botanical gardens worked in tandem with garden conservation geneticists and botanists to build living collections that support ex-situ (outside the wild) conservation and in-situ (in the wild) restoration. Scientists are answering questions about how many plants are needed in collections to adequately represent wild populations. They are also asking questions about what kind of genetic diversity current collections hold. How can we efficiently enhance that diversity with trips to the field for seeds and cuttings, and how can we effectively manage our collections so that we do not have redundant plants that take up valuable time and space?

From the horticultural side, there are questions about how to grow plants. Commercial nurseries are experts at propagating plants of commercial value. Ecologists and restoration practitioners are the experts at restoring wild populations but do not typically have horticultural training. Where does the expertise lie for growing those plants that no one has grown before? Or for which no one cares about besides those trying to save them from extinction? If we store seeds in a seed bank, what value is there if we do not know how to germinate the seed or grow the plants upon germination? That expertise and capacity is in the botanical garden space.

Grass trees (Xanthorrhoea sp.) rescued from a mine site and planted in RBGV- Cranbourne, where Australian native plants are on full display.

Much inspiration is being drawn from the zoo model, where animal pedigrees are tracked to minimize inbreeding and inform collection development. Botanic Gardens Conservation International is currently repurposing software that zoos use to fit garden collections and hope to make it available in 2023. In a world where resources (space, money) are limited, pedigree tracking would allow gardens to more effectively manage plant collections without intense, expensive genetics work. In practice this is not dissimilar to how dog breeders might find a mate for their beloved golden retriever. Regardless of pedigree tracking, there is a consensus that no garden can conserve everything. Meta-collections — collections of single species across many gardens — are key to plant conservation at gardens. If Holden can steward a subset of plants of a rare oak species and 10 other gardens in the world can do the same, then we are on our way to conserving that species.

Conservation horticulture is a space I hope Holden can grow into more. It takes a conscious effort when in the field to sample in a meaningful way, rather than grab every seed you see, and it takes even more effort to grow and maintain those collections once the seeds get to the garden. The Congress was eye-opening in this regard, and I cannot wait to explore this more deeply.

Connor Ryan is the Rhododendron Collections Manager at Holden Forests & Gardens, which means he has a hand in all things rhododendron at HF&G. Prior to coming to Holden, he earned a bachelor’s degree in Plant Science from Auburn University and a master’s degree in Plant Breeding, Genetics and Genomics from the University of Georgia. In the growing season, he can most frequently be found at Holden’s David G. Leach Research Station, where he leads an ornamental plant breeding program and stewards a vast collection of named and unnamed rhododendron hybrids. Connor started at Holden in spring 2019.