The continuous increase of the global human population living in cities has significantly impacted various aspects of nature and climate worldwide. One initiative to promote the urban green space and its biodiversity is the construction of green roofs. Despite the basic structure of these green roofs being similar around the world, the optimal design can depend greatly on local environmental conditions. In the Netherlands, it remains unclear how the flowering performance of green roofs can be enhanced beyond the relatively short flowering period of commonly used Sedum species. This study investigates the effects of adding mineral wool and compost to experimental green roof systems in the Netherlands. Mineral wool was applied as a water-retentive substrate layer, while compost was added as a nutrient-amending component. Flower and seed production, as well as plant species richness, were used as indicators of flowering performance on the green roofs at ground level. The results showed that mineral wool significantly increases the number of flowers and seeds, and the overall richness of plant species, stimulating both sown and spontaneously colonising species. The addition of compost did not affect these parameters. These results reveal that green roof designs incorporating water-retentive substrate components can enhance flowering performance, and suggest an expansion of the flowering period of green roofs in the Netherlands. This study evaluates these results in the context of the current state of green roof construction and management in urban areas.
Over the past decade, the condition of the rhododendron collection in the Botanical Garden of Copenhagen has gradually declined. In 2020, the Garden initiated a project to save its rhododendrons with a new landscape plan that is more ecologically authentic and more closely represents the genus’s natural environment. The project involved relocation and propagation of the plants while simultaneously introducing a new visual interpretive design for communicating the stories related to rhododendrons. In this article, we describe the endeavour of establishing a new home for the Garden’s rhododendron collection – comprising approximately 200 species, some of which are threatened – in the newly established Rhododendron Quarter. Today, this site is one of the most popular areas of the Garden, a place where visitors can slow down, enjoy the plants and gain knowledge through the interpretive displays.
Rhododendron chapmanii is a federally endangered, Florida-endemic shrub with a highly restricted and fragmented distribution. Updated field surveys reveal steep population declines across its range due to habitat loss, fire suppression, hurricane damage and over-collection. In response, the Atlanta Botanical Garden (ABG) has implemented an integrated conservation strategy that combines in situ monitoring, demographic research, and comprehensive ex situ safeguarding. Conventional hardwood and semi-hardwood cuttings achieved 70–80% rooting success by ABG’s conservation horticulture team. A new, efficient micropropagation protocol was developed using Anderson’s Rhododendron medium supplemented with zeatin and indole-3-butyric acid, enabling rapid, genetically stable shoot proliferation and high rooting rates. These propagation techniques support the efforts to expand the species’ safeguarded genetic base, reduce pressure on wild populations, and provide high-quality plant material for planned reintroductions guided by species-distribution modeling. This integrated approach positions ABG as a key leader in the recovery of R. chapmanii, demonstrating the critical role of coordinated propagation, genetic safeguarding and habitat management in preventing extinction of narrowly endemic plants.
Ilex spp. (holly) are widely planted ornamental evergreen shrubs which perform both an aesthetic and an ecological function in gardens. In Edinburgh, I. aquifolium is the second most common tree after Acer pseudoplatanus (sycamore), providing food and shelter for a range of species. Unfortunately, holly is under attack from a disease caused by the pathogen Phytophthora ilicis. This understudied pathogen has been in the UK for at least 35 years, but the impact has not been clearly elucidated. We undertook a study at the Royal Botanic Garden Edinburgh to understand the impact of this disease on Ilex spp. within a botanical plant collection. Our survey showed 14% of the collection was confirmed to be infected with P. ilicis, although true prevalence is probably underrepresented due to seasonal factors and detection challenges. We discuss possible management strategies for this disease.
The genus Rafflesia R.Br. ex Gray (Rafflesiaceae) produces the world’s largest flowers, yet most species are critically endangered, making the flower a symbol of global plant conservation. As a holoparasite confined to the woody vines of its sole host, Tetrastigma (Miq.) Planch. (Vitaceae), Rafflesia remains notoriously difficult to study and propagate. Its cryptic endophytic life cycle – persisting as microscopic tissue within its host for years before emergence – has long impeded ex situ conservation, such that its cultivation has aptly been described as ‘growing a plant you cannot see’. Grafting of infected host material has been the only proven method. After more than a decade of diverse attempts, we report the first viable propagation of R. speciosa Barcelona & Fernando-infected pieces sourced from the Philippines at the United States Botanic Garden in Washington, DC – the first documented cultivation of Rafflesia in the Western Hemisphere. Our approach combined two complementary methods: (1) rooting infected stem and root cuttings, and (2) grafting infected root tissues onto established Tetrastigma vines. Infection was verified using a combined molecular (PCR) and histological diagnostic framework. Notably, one graft produced two Rafflesia buds (cupule stage) approximately 2.5 years post-grafting, representing the first evidence of bud initiation outside Southeast Asia. This study (1) establishes replicable glasshouse propagation protocols for Rafflesia-infected Tetrastigma; (2) demonstrates a practical PCR-histological approach for confirming infection prior to budemergence; and (3) shows that infected tissues can preserve endophytic germplasm beyond the lifespan of the original scion. These outcomes were achieved despite the formidable logistical barriers of transcontinental permitting and transport, involving a legally protected Philippine endemic and a US-regulated organism. These methods mark a breakthrough in ex situ Rafflesia conservation, safeguarding vital germplasm and strengthening the future of in situ recovery efforts, enabling the maintenance of this cryptic parasite within its host until it emerges as one of the world’s largest flowers.
The Plant Listing at the National Trust for Scotland (PLANTS) project was a three-year plant collections inventory project that ran from 2022 to 2025 and spanned 35 gardens across Scotland. The project was conceived to deal with a plant-recording backlog and aimed to create an accurate set of plant records held in a centralised database. The gardens were inventoried during the summer months and the data collected input into the National Trust for Scotland plant records database and matched with any existing records over winter. At the end of the project the number of accession records held by the organisation totalled 150,000, representing 77,000 living accessions and 86,000 living collection items.
Next-generation sequencing (NGS) can generate gigabytes of genome data. Unlike Sanger sequencing, NGS generates a ‘read’ from a single DNA molecule, reflecting directly the starting DNA, including non-target organisms such as symbionts and pathogens. Non-target organism sequences are usually discarded during genome assembly as contaminants; these are potentially a great source of information for understanding the microbiome surrounding the plant. The present study explores bioinformatically the identification of the non-target organisms from genome NGS datasets of two cultivated Gesneriaceae species. The datasets were generated using different NGS technologies: one is from Streptocarpus rexii (Bowie ex Hook.) Lindl., sequenced using Oxford Nanopore Technologies long-read sequencing, and the second from Aeschynanthus angustifolius (Blume) Steud., sequenced using Illumina short-read sequencing. The reads were first assembled and then analysed using BlobTools to identify the contaminants. For S. rexii, Actinomycetota and Basidiomycota occupied the highest ratio among genome contaminants, followed by Arthropoda, Ascomycota and Acidobacteriota. In A. angustifolius, the highest contaminant class was Pseudomonadota and the second Actinomycetota, followed by Basidiomycota and Chordata. Arthropoda included mealybugs which were also observed in the glasshouse. The differences in contaminant composition between S. rexii and A. angustifolius may be linked to the relatively short-lived leaves of the former and the long-lived ones of the latter. This pilot study demonstrates that, in principle, this method is suitable to detect and identify associated organisms, and the pipelines designed here greatly facilitated this process. This approach might be useful in a horticultural setting for the assessment of plant material in quarantine or biosecure conditions and may be able to detect pathogens prior to plants showing symptoms. It also has potentially more widespread applications for studying plant–microbiome interactions.
Targets have been set within the Global Biodiversity Framework to increase in situ and ex situ conservation activities to address the biodiversity crisis and impacts of climate change. This paper highlights the horticultural skills and facilities held in botanic gardens that can make an essential contribution to these conservation activities and that are often termed ‘conservation horticulture’. Previously published research identified a lack of cohesion in the use of this term. This research seeks to explain the reasons for this through analysis of both previously published data and new data. New data presented was collected through semi-structured interviews with practitioners involved in conservation horticulture programmes in Europe, Asia, Australasia and North America. Key findings include the need for an understanding of conservation and horticultural principles, and the importance of research, teamwork and communication to deliver conservation horticulture projects. A theme map of the findings is presented as are factors to be considered when planning conservation horticulture projects.
The range of topics covered by papers published in volume no. 24 demonstrates the significance of botanic garden horticultural knowledge, research and facilities for conservation and understanding the world of plants. There is a theme of conservation horticulture running loosely through many of the papers. The prevalence of this theme, which was not an intentional editorial decision at the outset of the volume compilation, illustrates the prominence that the term ‘conservation horticulture’ has rightly gained in our botanic garden community.
Conservation Horticulture (1) is an essential, central aspect of modern botanic garden culture and operations, (2) cannot be separated from botanic gardens and (3) produces positive outcomes in every other programme with which it intersects. Here, given the inseparable nature of each, a definition for Conservation Horticulture is provided along with an aligned definition of Botanic Garden. The concept of Conservation Horticulture is illustrated with examples.
Botanic gardens and arboreta maintain globally important collections for conservation and education. Many organisations hold a reputation for excellence in propagation, cultivation and collection preservation. Learning from successes and challenges, and having the ability to disseminate that knowledge, is paramount for improving techniques and outcomes. However, the field of horticultural research is not well defined, and results of plant cultivation techniques are often only shared informally rather than published. This study was designed to explore how horticultural research practitioners perceive the field of horticultural research and excellence, how they and their institutions are involved, and what are the most urgent needs of future horticultural research among gardens and arboreta in the United States. An online survey was distributed to ascertain the status of horticultural research amongst the United States members of the American Society for Horticultural Science, the American Public Gardens Association, Botanic Gardens Conservation International and the Interactive Community of Arboreta, Level II, III and IV members. The survey was completed by 128 respondents from 34 US states across 116 institutions. The responses highlight the fact that horticultural excellence is holistic – focusing on species conservation, ecology and pest mitigation. The findings also touch on the status and involvement of respondents in horticultural research and their perceived needs for future research. These responses further highlight challenges such as funding, time and personnel shortfalls. Horticultural research also includes an emphasis on practical approaches, requiring better recognition and sharing methods. The findings introduce a new framework to support the horticulture community in conceptualising, communicating and implementing research. This framework proposes that horticultural research can be broadly categorised into two overarching approaches: practical and technical.
Established in 1974 within the Universiti Malaya campus, the Rimba Ilmu Botanic Garden is Malaysia’s first university botanic garden. Occupying nearly 60 ha in the Klang Valley, Malaysia’s most populated metropolis, Rimba Ilmu has evolved from an abandoned rubber plantation into a garden of 1,300 planted species, with many more spontaneously established. Unusually for a botanic garden, it eschews a formal flower garden aesthetic in favour of a tropical forest one: natural processes shape the Garden and its inhabitants alongside human-directed curation. As one of the last large green lungs in the Klang Valley, Rimba Ilmu provides essential ecosystem services to the city. The site houses the oldest and largest university herbarium in Malaysia, Universiti Malaya Herbarium (KLU), where 81,000 specimens are stored. Since the late 1990s, Rimba Ilmu has played a role in public environmental education, supported by facilities such as its Rare Plants & Orchid Conservatory and Rain Forests & Our Environment permanent exhibition. Rimba Ilmu has a community-oriented ethos. It has long supported the participation and development of volunteers, and continues to welcome collaborations with diverse partners. Holding on to a mission of research, conservation and education, Rimba Ilmu is part of the United Nations University’s Regional Centre of Expertise on Education for Sustainable Development Central Semenanjung. In 2024, Rimba Ilmu celebrated its 50th anniversary with a series of public events and a specially commissioned exhibition, Belukar dah jadi Rimba.
After the critically endangered conifer Wollemia nobilis (Wollemi pine) was discovered in late 1994, an urgent task was to determine its cultivation requirements so that an ex situ population could be established. Propagation from extremely limited material was the first challenge, followed by development of a genetically representative ex situ conservation population. While the ex situ population was developed for insurance against loss of diversity in the wild population, it has also been used for research, and as the source of material for translocations, dispersed garden plantings and a botanic garden metacollection. Here, we report how these challenges were approached, based on nascent understanding of W. nobilis – as an Araucarian and as a rainforest emergent. As studies into the morphology and biology of the species progressed, these findings were used to refine propagation techniques. The establishment of this species in gardens around the world has expanded our knowledge of its biology and ecology. Insights concerning its behaviour in cultivation include its intolerance of extreme heat, extreme cold, high light and drought, and a preference for free-draining and acid soils – conditions approximating to its temperate rainforest origin. Now that these garden plants have begun to produce seeds, there is the opportunity for deeper research into factors influencing seed viability and plant establishment from seeds. This paper reviews many of the published studies aimed at understanding various aspects of W. nobilis biology, particularly those relevant to informing its requirements in cultivation. We also present data and conclusions drawn from unpublished studies which cumulatively aid efforts to conserve the species ex situ.
While historically serving ornamental, medicinal and agricultural purposes, botanic gardens and arboreta have opened their doors to the public and have extended their missions to encompass the study, preservation and support of plant diversity. Longwood Gardens (Kennett Square, PA, USA) has embarked on this journey, leveraging its scientific expertise to establish a conservation focus. Navigating this initiative with its strength in horticulture, the Longwood team outlines key steps in creating a conservation horticulture programme, emphasising the importance of (a) assessing horticultural competencies, strengths and existing infrastructure; (b)aligning systematic conservation priorities and global need; (c) amplifying impact through partnerships; (d) developing research initiatives and expanding mission-aligned work; and (e)leveraging audiences. The article concludes by emphasising the importance of collaborative partnerships, avoiding mission creep through maintaining a strategic focus and understanding that a continuum mindset is essential. Longwood’s work, focusing particularly on terrestrial orchids, illustrates how a public garden can use this process to result in a successful and strategic impact-focused conservation horticulture programme that supports plant diversity.
Digital library searches undertaken by the author have recently uncovered a small but significant archive of information about the Benmore fernery, linking it to glasshouses and other contemporaneous fernery buildings in Scotland. It is now possible to verify the date of the original building to the early 1870s. Wider context and background details are provided by briefly exploring horticultural trends and architectural innovations from this period. Thereafter, the known Clydeside fernery buildings constructed by James Boyd & Sons are reconsidered, providing insight into unknown and previously missing details of the Benmore version. In 2009, from a ruinous condition, the Benmore fernery was the subject of a significant restoration led by a Glasgow-based team of conservation-accredited architects. Aspects of this practical work are summarised. The article concludes by exploring the wider topics of garden history and conservation and highlights the role of botanic gardens in promoting the sometimes overlooked value of garden heritage.
Primula palinuri Petagna is an endangered species endemic to a tiny coastal area in southern Italy. Investigating the possibility of growing and propagating this endangered species with ex situ actions should be encouraged, as this could provide a second line of security for rare plants by allowing specimens to be grown in the absence of natural environmental challenges. Currently, the Royal Rotterdam Zoological and Botanical Gardens (RRZBG) hold 31 accessions of P. palinuri, which represents an ex situ collection with potential value for conservation programmes. Over the years, horticulturists at RRZBG have created a solid protocol to produce viable seeds through hand-pollination techniques, thus allowing conservation programmes for this species to become more effective. In this article the cultivation of the species is described, including information on seed germination, general maintenance, cultivation to flowering stage and propagation from the resulting seeds.
Wittsteinia vacciniacea F.Muell. (Baw-Baw berry) is a vulnerable evergreen trailing shrub dating back over 70 million years, when Australia separated from Gondwanaland during the late Cretaceous period. It is the only species of Wittsteinia to occur in Australia, and one of four genera in Alseuosmiaceae. The Baw-Baw berry is restricted to a few mountainous populations of varying size and occupancy within Victoria. The fragrant flowers are attractive pendent yellow-red bells, and the globose fruit a greenish-red berry with persistent attractive calyx lobes. It is the combination of a trailing habit and floral features that make this species an ideal candidate for amenity horticulture. To test this, we collected plant material from five of the six known localities in Victoria and, using stem/cutting material with +/- Clonex® gel and either Jiffy® Plugs or a perlite/vermiculite mix +/- Clonex®, achieved 60.8 per cent root initiation overall. Greater root development was achieved using the plugs, and there were differences between root initiation and species locality. The hormone treatment proved unnecessary to ensure root initiation. To test germination response, seed was collected from Mt Baw Baw, which supports the largest population. Preliminary work on fresh seed indicated a high fill rate, determined by x-ray imagery, and a 90 per cent germination response at 20/15 °C with gibberellic acid (GA3). We explored the germination niche using a thermogradient plate and determined an optimal temperature of ~17 °C. Resulting vegetative and seed-based propagules have been incorporated into the Royal Botanic Gardens Victoria living collection, as part of a broader ex situ conservation strategy. Further to this, using predictive modelling, we found areas outside this species’ current distribution that may be suitable for future plantings, ensuring the Baw-Baw berry’s survival beyond its current refugia.
The aim of PlantNetwork’s Target 8 project is to involve botanic and other collections-led gardens throughout Britain (and eventually Ireland also) to cultivate nationally threatened vascular plant species. In this way, if each garden were to ‘adopt’ 2–3 threatened species then the network of British botanic gardens could collectively cultivate almost all of the 204 threatened species found in Britain, and therefore fulfill the requirements of Target 8 of the Global Strategy for Plant Conservation. However, before such a project could start, baseline information on the number and diversity of threatened plants in British ex situ collections was required. Along with this, species dossiers compiling cultivation and conservation details were considered necessary for the success of the project. Furthermore, practical details of the project such as collection and representation needed to be discussed with curators. This paper describes the background, survey work and practical aspects of the project.
Conservation horticulture is an emerging and increasingly important function for all botanic gardens, but it is an activity that can be difficult to explain and to promote. Part of that difficulty lies in its name, and a few alternatives are suggested in this Guest Essay – such as Care for the Rare, Raising Rarity, and Plant Rescue and Care Unit – all currently in use at Royal Botanic Gardens Victoria (RBGV) for more narrowly scoped but pioneering projects. In reimagining conservation horticulture at RBGV we want to draw on the public’s intrinsic interest in and affinity with plants, rather than taking a defensive stand against what is often called ‘plant blindness’. Raising Rarity 2.0 is likely to combine commercialisation of rare species, innovative blending of amenity and conservation horticulture, and even stronger partnerships with schools and local government. As I prepare to leave RBGV after 25 years in senior management of botanic gardens, I’m supporting a grassroots push from horticultural and research staff to add conservation horticulture (whatever we call it) to our already potent mix of nature, culture and science.
Conservation horticulture is an emerging and increasingly important function for all botanic gardens, but it is an activity that can be difficult to explain and to promote. Part of that difficulty lies in its name, and a few alternatives are suggested in this Guest Essay – such as Care for the Rare, Raising Rarity, and Plant Rescue and Care Unit – all currently in use at Royal Botanic Gardens Victoria (RBGV) for more narrowly scoped but pioneering projects. In reimagining conservation horticulture at RBGV we want to draw on the public’s intrinsic interest in and affinity with plants, rather than taking a defensive stand against what is often called ‘plant blindness’. Raising Rarity 2.0 is likely to combine commercialisation of rare species, innovative blending of amenity and conservation horticulture, and even stronger partnerships with schools and local government. As I prepare to leave RBGV after 25 years in senior management of botanic gardens, I’m supporting a grassroots push from horticultural and research staff to add conservation horticulture (whatever we call it) to our already potent mix of nature, culture and science.
