Backyards, balconies, parks, schools, and allotment gardens could contribute to the survival of almost 1,000 species of rare plants in Germany, according to a new analysis.
The findings offer a first look at the potential real-world impact of conservation gardening, a growing movement that seeks to recast public and private gardens as not just aesthetically pleasing green spaces but also refuges and dispersal corridors for declining native plants.
That contrasts with the conventional approach to gardening, which emphasizes a small suite of often non-native ornamental plants, and results in gardens that are pleasing to the eye but have relatively low biodiversity.
“It is estimated that two out of five plant species are at risk of extinction. In order to tackle this biodiversity crisis, novel approaches are needed that do not view humans and biodiversity as a dichotomy,” says study team member Ingmar Staude, a botanist at the University of Leipzig in Germany. Conservation gardening can help by both increasing public awareness of the biodiversity crisis and getting people directly involved in helping reverse it, he adds.
Staude and his collaborators first compiled the names of all endangered, threatened, and extinct in the wild plants across 16 German states from the IUCN Red List. German states host anywhere from 515 to 1123 red-listed plant species, the team writes in a paper published in Scientific Reports.
The researchers collated information about these species on NaturaDB, a clearinghouse of gardening information, to see which ones are known to be suitable for cultivation in gardens. Overall, 988 species of plants on the Red List in Germany could be protected in gardens. The proportion of garden-friendly red-listed plants in each state ranges from 29% (321 out of 1123) of threatened plant species in Bavaria to 53% (352 out of 670) of such species in Hamburg.
The team then combed through the websites of six major nurseries specializing in native seeds and plants looking for red-listed species for sale. Of all the species suitable for gardening, 66% (650 species) are already commercially available, they found.
“I was surprised to see that so many red-listed plants are already commercially available,” Staude says. “Contrary to the common assumption that these species are declining unnoticed, only known to the expert botanist, this highlights a considerable expertise in propagating these species (at least in Germany).” More studies will be necessary to suss out the situation in other countries.
Another rare-plant myth busted by the study: the idea that endangered plants are delicate and need coddling. Of the red-listed plants known to be suitable for gardening, 45% prefer dry soils, in contrast to just 27% of conventional garden plants. What’s more, 25% of conservation-garden species prefer nutrient-poor soils; just 7% of conventional garden plants thrive in such conditions, while 60% prefer nutrient-rich soils.
There’s also a substantial suite of conservation-garden plants that prefer wet habitats, which might be able to help recycle gray water and tame the urban heat island effect in cities. Together, such findings suggest that conservation gardening could also be a strategy for climate change adaptation.
If conservation gardening went mainstream and widespread cultivation of red-listed plants were to succeed at halting their decline, the approach could reduce the proportion of plant species on the Red List by up to 50% in some German states, and up to 25% in Germany as a whole, the researchers calculated.
Admittedly, there are some big ‘if’s behind that conclusion. “We are currently studying whether cultivation benefits species population trends in the broader landscape and whether endangered plant species systematically differ in dispersal or germination traits from those that are currently increasing,” Staude says. “This will be important to understand for which species gardens can act as drivers for plant dispersal.”
Expanding conservation gardening will require ramping up the ability to produce plants for purchase (the nurseries in the current study are relatively small and specialized) while still keeping an eye on ecological factors like genetic diversity and locally adapted varieties, Staude says. It will also require a collective reframing of what gardens are for and how they should look.
Garden and landscape design have undergone numerous transitions throughout history. For instance, in Europe, most gardens until the Renaissance featured medicinal plants rather than ornamental ones. Nowadays, medicinal plants are not a prominent feature in most gardens,” says Staude. “Similarly, during the Baroque and Rococo periods, gardens were geometric and highly formal, but today gardens tend to have a more naturalistic appearance.”
To help disseminate practical information about conservation gardening, the researchers created a web app in which users can filter plants by region, growing requirements such as light demand, and Red List category. The app has links to growers offering particular species for sale, and also includes a “knowledge gap” section (since the 2,474 species of red-listed German plants not known to be suitable for gardening might simply reflect that people haven’t tried to cultivate them – not that they won’t do well in gardens).
The app also includes a list of plants suitable for growing on balconies or green roofs – putting biodiversity conservation within reach even for people with without access to traditional garden space. In the future, the researchers aim to establish an example conservation garden in a Leipzig allotment garden, Staude reports. “We aim to involve schools, nurseries, and allotment societies in the construction and maintenance of such a garden, hoping that it may communicate the concept of conservation gardening,” he says.
Source: Munschek M. et al. “Putting conservation gardening into practice.” Scientific Reports 2023.