Friday essay: cure or kill? The deadly serious world of poison gardens – and why I planted my own

Not every plant is your friend. Not every plant is good. I know this because I’ve been researching the history of poison gardens and have planted a modest one in my small Sydney backyard.

A poison garden contains only toxic plants, which could kill humans if consumed in varying quantities. The concept of a poison garden grew from the 16th to 17th century history of herbalist or apothecary gardens, where plants and herbs were grown for medicinal purposes, mostly by doctors and monks.

These early gardens flourished at a time when herbals, hefty reference books on medicinal plants, were produced. An example is John Gerard’s 1500-page book The Herball (1597), which included English plants and herbs but also exotics collected from the “new world” (colonised countries such as the Caribbean islands). Within these apothecary medicinal gardens, specialist planting areas were sometimes allocated to exotic carnivorous, aquatic or poisonous plants.

Italy’s Padua Botanical Garden, dating to 1545, includes poisonous plants. Such gardens were established for reasons of natural history, botanical education and medicine but also as places of spectacle or intrigue. And there was a lot of intrigue in 16th and 17th century Italy and France, with flourishing small poisons businesses, usually run by women. Catherine Monvoisin, for instance, had a thriving consultancy as a poison supplier in Paris, until she was tried for providing lethal poisons in a murder plot and executed in 1680.

Most poisonous plants have qualities of cure and of medicinal care … but they are also dangerous. This is what Greek philosopher Plato called pharmakon – the idea that plants can cure, but they can also kill if the dose is high enough. The trick is knowing those thresholds.

To honour the medieval tradition, my poison garden is planted in a circular, raised garden bed, hip-height. There is, of course, nothing illegal about growing plants that contain high levels of poison compounds. Poisonous plants are potted up in many living rooms and suburban backyards.