Elizabeth Wilks: Mauri tū! Mauri ora!
New Zealand Garden Trust gardens are the pinnacle of New Zealand horticultural expertise. The gardens pioneer designs and ideas which filter through to create trends in private gardens both within New Zealand and beyond. The species we showcase and the plant communities we create others aspire to. Our gardens are role-models. As we increasingly focus on climate resilience and environmental sustainability, we encompass Beth Chatto’s right plant, right place, reducing inputs of water and chemicals while improving plant health. On the surface this is positive; but herein lies a dichotomy: exotic species which thrive in Aotearoa without human intervention have a higher risk of invading wild ecosystems. Our good faith efforts to increase garden resilience may result in the obverse for the wider environment. This leads me to question whether the English phrase which has guided our gardening for over sixty years is still appropriate for New Zealand. I would like to suggest a more nuanced kaupapa; one which recognises the impact our garden plant choices can have on fragile endemic ecosystems.
I want to share some numbers.
2522. The number of native vascular plant species in Aotearoa.(1)
25,000. The number of exotic plant species humans have introduced to New Zealand.(2)
Those are not misprints: every native flora species is out-numbered ten to one by exotics.
Around 10% of exotic plant species become naturalized: 2684 exotic species grow in self-sustaining wild populations.(1) There are now more naturalized exotic species than native species. Species with well-developed dispersal mechanisms spread seed, root or stem material far from the parent plant, and some become invasive weeds. Currently at least 386 naturalized exotic species are identified as environmental weeds(3) and they form a significant threat to 46% of New Zealand indigenous plants.(1)
Three quarters of environmental weed species were introduced solely as garden plants: someone from our tribe of gardeners loved the aesthetics of a plant they saw overseas and brought it into New Zealand. Ministry for Primary Industries now guards our external border and limits new introductions. However, many problematic species are already here and as gardeners we are a key part of their management. Erigeron karvinskianus (Mexican Fleabane) has frothy buoyancy and joyful effervescence. That buoyancy allows thousands of tiny, wind dispersed seeds to spread far and wide. E. karvinskianus is one of 135 species in the National Pest Plant Accord.(4) The Accord contains species where horticulturalists have been identified as the key source of dissemination. The sale and informal distribution of these plants is prohibited, but last year one of New Zealand’s garden magazines promoted E. karvinskianus as a top plant for dry gardens. E. karvinskianus is in four South Island open gardens that I know of. One owner commented to me “I love it and keep it under control.” How? Another offered me some seedlings. These examples demonstrate naive ignorance from gardeners.
What is a weed? As gardeners we know this is a fraught question: something I nurture to survive in Canterbury may thrive in Wellington; dominate and invade in Auckland and vice versa. A weed definition that resonates with me is in a report by Rob McGowan: “A plant that upsets the balance Papatūānuku needs to be well […] A plant that disrupts […] natural balance.”(5) In other words the way a plant interacts with ecosystems is the pertinent issue. Lupinus polyphyllus (Russell lupin) is a very visible weed. Many New Zealand gardens contain this exotic species. Their spires form vivid exclamation marks in early summer. Tourists adore the seas of indigo, amethyst and violet oblivious to the far-reaching web of environmental repercussions. Lupins release allelopathic chemicals which inhibit germination of native flora. Their woody form shades out native plants and basal leaves cover potential ground nesting sites for birds. They modify mycorrhizal networks and their nitrogen fixing ability enriches river silts, increasing risk of invasion by other weeds. Lupins bind braided river gravels, reducing lateral channel movement while increasing vertical erosion. This means river channels deepen to the point where endangered wading birds such as Black stilt/kāki can no longer stand in the water to feed near their breeding grounds. Every aspect of the ecosystem is impacted. All environmental weeds in Aotearoa unleash a similar litany of disruption. Ecological balance is the crux of why exotic plant naturalizations are a problem in New Zealand; it may also hold the key to a paradigm shift for gardeners.
Lomaria Discolor on Thompsons Saddle Track which inspired a garden design.
I have a botanist friend whose Christchurch garden is unmodified clay pan. She has not dug in compost, or in any way sought to ameliorate her soil. The ornamentals are all endemic to Christchurch. The garden is unusual and lovely. Her thinking is that any non-endemic plant is a threat to wild ecosystems. I respect this perspective, but suspect it is unrealistic to expect everyone to adopt such a purist approach. Many ornamental exotics have been cultivated in New Zealand for over 175 years and not naturalised; while some native species have become weeds outside their endemic range.(6) In my home garden exotic Hosta, Pulmonaria and Epimedium rub shoulders with native Anemanthele lessoniana, Lomaria discolor and a miscellany of Parablechnum and Adiantum species. In full sun exotic Agastache rupestris, Echinacea pallida and Salvia lanceolata dance alongside native Kanuka ericoides ‘Little Fox’, Dianella nigra and Astelia nervosa. For me, the debate is more nuanced than native versus exotic. Instead the nexus is three-fold: sensitivity to natural balance, assessment of eco-system risk and responsibility of being a role model. Coming to this conclusion set me searching for a uniquely New Zealand kaupapa.
Māori whakapapa is earth-centric, prioritising Papatūānuku where mauri is a vital life essence. Mauri symbiotically connects all living things: the largest noble trees of the forest to the smallest soil micro-organisms and their human caretakers. (5) Ecological science agrees: all living things need each other to survive and their strength is in the web of connections. Mauri tū is earth’s life force, protective, spiritual genius loci. Mauri ora is life’s potency, a flourishing energy. Together mauri tū and mauri ora reflect a vigorous but grounded vitality: the essence of balanced and sustainable life. I believe using mauri tū, mauri ora to guide our thinking and decision-making ensures we make more resilient and sustainable garden choices for Aotearoa.
Regional Councils prioritise funding around species posing the greatest threat to their local environments. This can lead to anomalies. Sale of Psidium cattleyanum (Cherry guava) is restricted in Tāmaki Makaurau but it can be purchased in Northland (despite also being a weed there). This nonsensical situation increases the importance of our position as caretakers of Papatūānuku. As gardeners we pride ourselves on green-fingered common sense, so let’s apply it: for example, the climate and environment of North Canterbury is not very different from that of southern Marlborough, so a weed in one province is likely a problem in the other. In addition, climate change means we need to look beyond regional boundaries to corollary climates. Plants that are currently weeds in Hawkes Bay are likely to become problems in Marlborough and Canterbury in the near future. We can choose to take an approach that minimizes risk to native ecosystems: when we follow the more stringent restrictions we respect mauri tū, mauri ora.
Using mauri tū, mauri ora we accept individual responsibility to be informed and take appropriate action. We can each check online whether the plants in our gardens are on the Department of Conservation Environmental weed list(3) or the regularly updated Manaaki Whenua Weed Key.(7) Scientists like to be certain of their facts. By the time a species has been identified as an environmental weed, the evidence is unequivocal: these species have been rigorously assessed as severe and far-reaching threats to native ecosystems. I believe these plants have no place in gardens anywhere in New Zealand. The issue is not just whether the plant can “escape” from a specific location; for open gardens it is one of role-modelling. A visitor might decide to replicate our plantings, and we have no control over where those plants are installed and how they are managed. The National Pest Plant Accord does not require removal of listed species partly because gardeners dumping plant material beside roads, rivers and wild spaces increases species colonization. In my experience, NZGT members have ethics, knowledge and capacity to dispose of environmental weed material appropriately. Let’s do so. Mauri tū, mauri ora is a clarion call to select alternate species, ones which can be replicated in other gardens with zero or minimal ecosystem threat.
‘Sleeper species’ are plants with the potential to become environmental weeds as climate or other conditions change. Invasion time lag means we do not generally see the repercussions of our horticultural decisions. We have all battled with plant thugs in our gardens, but their behavior usually manifests within a year or two. The delay from species introduction to the development of a self-sustaining wild population is typically 20-30 years.(2) Woody perennials can take a century between introduction into gardens and naturalization.(8) Rates of species introduction to New Zealand dramatically increased between 1950 and 2000: naturalizations are still ramping up.(6) Monitoring indicates 20 new species currently naturalise every year.(2) We consistently underestimate the non-linear trajectories of invasions.(6) Initially only a few plants appear in the wild, with numbers swelling exponentially as an invasion occurs.
New Zealand largely relies on eagle-eyed citizen scientists to identify emerging trends. Ecologists encourage us to log observations on iNaturalist.(9) For me this requires a shift from horticultural thinking: “Oh, that’s lovely…” to mauri tū, mauri ora - environmental thinking: “Ooo, that could become a problem…” Visiting Auckland gardens I revel in the lush epiphytes; I enjoy seeing huge exotic Platycerium bifurcatum (Staghorn ferns) perching in trees. In Christchurch I grow one in my bathroom, so observing them thriving outdoors is both a novelty and delightful. On one walk I noticed juveniles on tree branches some considerable distance from cultivated adult plants. The thought niggled, and when I returned home I googled the words “staghorn fern pest NZ” and up popped a 2023 NZ Journal of Ecology paper measuring their establishment in Auckland urban forests and recommending on-going monitoring due to potential for naturalisation.(10) Ferns reproduce with airborne spores. The staghorn ferns I saw are in exotic, urban trees a long way from wild ecosystems, but what happens if gardeners replicate these plantings close to the Waitākere Ranges? To me monitoring feels like an ambulance at the bottom of a cliff. Gardeners guided by mauri tū, mauri ora can be a fence at the top of the cliff: Auckland gardens are absolutely stunning when laden with plants growing on plants. New Zealand has 108 native epiphytes including 39 ferns.(11) None have the same form as P.bifurcatum, but many are magnificent and could be used instead to quoin glorious epiphytic communities.
One way for us to assess environmental risk is to look for international corollaries.(2) I am contemplating using Euphorbia rigida in a Christchurch climate-resilient garden. Research reveals both E. rigida and the closely related E. myrsinites are environmental weeds in parts of the USA with similar climatic conditions to Canterbury. Conversations with NZ gardeners highlight the excessive seeding properties of E. rigida. Prolific seeding is not enough to make a species invasive, but it dramatically increases the threat. My ego is shouting: “E. rigida is a rock-star of dry gardens. Evergreen glaucous leaves form a structured whorl around upright stems. Chartreuse flowers soften to antique rose bringing colour and form to a largely senescent winter garden…” The voice of my conscience quietly but persistently counters: “The garden is a public, educational resource; people will mimic the plant communities I create. Think about the risk to river braids…” Mauri tū, mauri ora suggests my vanity takes a hike and I re-think my plant palette using a species with lower environmental risk.
In older gardens there may be a desire to retain heritage plants. If we lose them, we may never gain permission to bring them back into New Zealand, and our gardens will be poorer for the loss. However, while heritage collections are important, their value cannot eclipse our responsibility to endemic ecosystems: if New Zealanders do not protect Aotearoa, no one else can. Buddleja davidii is an environmental weed. During a mid-winter visit to inventory a public garden site I observed four enormous Buddleja and my initial reaction was less than diplomatic. I was politely but firmly informed by Council staff: “They are a heritage cultivar on a heritage site.” Oops! B. x weyeriana ‘Moonlight’ is a cross between B. davidii var. magnifica and B. globosa made by Major William van de Weyer in 1920: the first successful hybridization of a South American and an Asiatic species of Buddleja. So this is a rather special plant. I have now seen the flowers. The closed buds are a soft violet; they open to a rich cream, with vibrant orange centres: spectacular cones of hokey pokey. In the garden I find woody stems root with worrying ease, but an online search shows B. x weyeriana ‘Moonlight’ is a sterile hybrid. Having no viable seed reduces invasion risk. Perhaps this is an acceptable compromise between retaining heritage and respecting mauri.
My garden thinking and decision-making have shifted since I began using mauri tū, mauri ora as a lodestar. I am trying to place Papatūānuku before my ego. I look at both cultivated plantings and natural ecosystems with a different lens, cogitating on the web of life I am interacting with as a gardener. I accept my position as a role model and do not plant or retain species on the DOC Environmental Weed List.(3) I research potential impacts of my species choices in much greater depth than before and make risk-averse decisions. I still plant in a fusion style, but it is one with lower environmental repercussions.
“Mauri tū, mauri ora” combines core elements of genius loci with right plant, right place, in a uniquely New Zealand kaupapa. The phrase symbolises the web of connections that enables life in Aotearoa to thrive. Mauri tū, mauri ora cuts through the heated native/exotic debate and gives us a practical way forward: when we prioritise earth and ecosystem connections, we consciously create gardens in long-term symbiosis with our wild environments. Instead of selecting plants from an anthropocentric perspective we choose plants which sensitively cloak Papatūānuku. If we begin with mauri tū, mauri ora, our plant choices are guided by a desire to be far-sighted caretakers. This brings me back to my opening comments. As designers and gardeners we have a responsibility to model and practice true sustainability and environmental resilience in Aotearoa. Let’s bring New Zealand’s life force to the proscenium of our garden decisions. Mauri tū! Mauri ora!
Note: Elizabeth trained as an environmental scientist, specialising in New Zealand vegetation change during the Pleistocene and Holocene and also in NZ braided river systems. Currently she works part time in conservation and part time as a garden designer.
1. New Zealand Plant Conservation Network. Retrieved from https://www.nzpcn.org.nz/help/faq/new-zealand-plants/
2. Upton, S. (2021) Space invaders: A review of how New Zealand manages weeds that threaten native ecosystems. Parliamentary Commissioner for the Environment. Retrieved from https://pce.parliament.nz/media/czajngus/space-invaders-report-pdf-68mb.pdf
3. McAlpine, K. & Clayson, H. (2024). List of environmental weeds in New Zealand 2024. Science for Conservation. 340. 1-37.
4. National Pest Plant Accord retrieved from https://www.mpi.govt.nz/dmsdocument/3664-National-Pest-Plant-Accord-manual-Reprinted-in-February-2020-minor-amendments-only
5. McGowan, R. (2021) Mauri tū! Mauri ora! Māori perspectives on exotic plants in Aotearoa. Report prepared for the Parliamentary Commissioner for the Environment
6. Hulme, P.E. Plant invasions in New Zealand: global lessons in prevention, eradication and control. Biol Invasions 22, 1539–1562 (2020). Retrieved from https://doi.org/10.1007/s10530-020-02224-6
7. Dawson, M., Navie, S., James, T., Heenan, P., Champion, P. 2007–2025. Weeds Key – interactive key to the weed species of New Zealand. Retrieved from https://www.landcareresearch.co.nz/resources/identification/plants/weeds-key.
8. Kowarick, I. (1995) Time lags in biological invasions with regard to the success and failure of alien species. In Pysek, P., Rejmānek, M., Wade, M. eds. Plant invasions: general aspects and special problems. Workshop held at Kostelec nad Cernymi lesy, Czech Republic, 16-19 Sept 1993. Amsterdam, SPB Academic Publishing. Pp15-38.
9. Sullivan, J.J., Meurk, C.D., Dawson, M.I., Hutchison, M. (2019) Crowdsourcing the discovery of new plant naturalisations in Canterbury using iNaturalist NZ Canterbury Botanical Society Journal 50 Pp 54-66
10. Wu, J. and Brock, J. (2023) The invasion of non-native epiphyte Platycerium bifurcatum in Auckland’s urban forest canopy. New Zealand Journal of Ecology 47(1): 3542
11. https://www.nzpcn.org.nz/flora/vascular/flowering-plants/epiphytes/nz/nz-list/