A peer-reviewed review of New Zealand National Poisons Centre enquiries from 2003 to 2010 found 11,049 calls involving plants or fungi, out of just over a quarter of a million calls overall, and 80 percent of those plant-related calls involved children under 12. What stands out going through that research isn't some exotic rainforest species. It's a short list of completely ordinary plants already growing in a huge number of New Zealand backyards.
In order of how often they were actually phoned in about, the most common were black nightshade, daffodils, hemlock, karaka, foxglove and ongaonga (New Zealand's native tree nettle). Black nightshade alone accounted for 834 of those calls, 90 percent involving children, usually from the dark, blackcurrant-like berries looking temptingly edible. Daffodil bulbs cause real trouble because they can look enough like onions or spring onions to get mistaken for one in the kitchen. Foxglove, already flagged directly on this site's own foxglove plant page, has every part of the plant genuinely toxic if eaten. Karaka's raw seed kernel is toxic; traditionally Māori prepared it through a lengthy soaking, cooking and burying process specifically to remove that toxicity before eating it, not something to attempt informally. Ongaonga is the odd one out on this list: a wild native nettle rather than anything deliberately planted, and the only native plant confirmed to have killed someone, through the toxin in its needle-like hairs.
A few widely grown ornamentals not on that specific list are still worth real caution. Oleander is about as potent as garden plants get, with a single leaf cited as enough to be fatal to an adult; it's less common in New Zealand than in Mediterranean climates but is sold here and does turn up in warmer coastal gardens. Arum or calla lily is a genuinely frequent cause of poisons centre calls in its own right, its sap and leaves carrying oxalate crystals that cause immediate mouth and throat irritation if chewed. Rhododendron and azalea, both already on this site, contain grayanotoxins and are toxic enough to cause vomiting, drooling and, in a large enough dose, heart rhythm problems in pets.
Cats specifically face a danger most gardeners never think about: true lilies (the Lilium genus) and daylilies. Every part of the plant, including pollen groomed off fur after a cat merely brushes past one, can trigger acute kidney failure, and it's frequently fatal without fast veterinary treatment. Dogs aren't affected the same way, but a cut lily brought inside as a bouquet is a genuine, serious risk in any household with a cat.
Every part of the plant, including pollen groomed off fur after a cat merely brushes past one, can trigger acute kidney failure, and it's frequently fatal without fast veterinary treatment.
A couple of plants already on this site are worth a direct safety note here, since their own plant pages don't currently carry one. Hydrangea leaves and flower buds contain cyanogenic compounds and are mildly toxic to dogs, cats and horses, though a large amount needs to be eaten before symptoms show, and the most likely outcome is gastrointestinal upset rather than anything more serious. Kōwhai, this site's own feature native for attracting tūī, had its seeds and pods among the more commonly phoned-about culprits in the same poisons centre research, worth knowing if young children spend time under a flowering tree in spring.
None of this is really an argument for ripping plants out. It's an argument for knowing what's actually growing in a garden children or pets use, keeping a closer eye around anything on this list during the months it's flowering, fruiting or freshly mulched with fallen seed pods, and treating a suspected ingestion as worth an immediate call rather than a wait-and-see. The National Poisons Centre (0800 POISON, 0800 764 766) takes exactly these calls, and for a family garden, having that number saved is a more useful precaution than trying to memorise every toxic plant in New Zealand.