Inside England's deadly garden: A tour of toxic wonders

A unique treat awaits horror enthusiasts on the British Isles. Visitors are welcomed by a warning sign with the words: "These plants can kill." The iron gate is additionally adorned with skull symbols. Behind it lies the most poisonous garden on earth that can be visited.

The Poison Garden is a section of Alnwick Garden, established in 2005 in Northumberland County in northeast England. The garden can only be visited with a guide.

"Before visitors are allowed to enter, they must have a safety briefing," explains Dean Smith, a garden guide, in an interview with BBC Travel. He added that the visitors are strictly warned not to touch, smell, or taste any of the plants.

The Poison Garden features over 100 species of plants, including those with strong poisonous, narcotic, or hallucinogenic properties. The official garden website mentions cases of people fainting after ignoring recommendations and inhaling volatile toxins.

One of the most dangerous plants in the garden is aconite, also known as wolfsbane, which contains aconitine, a potent neurotoxin.

The most deadly plant, however, belongs to another species. "Probably the most poisonous plant we actually have here is ricin, better known as the castor bean or castor oil plant," claims Smith. "The Guinness Book of World Records considers that to be the world's most poisonous plant," he adds in an interview with BBC.

Surprisingly, many highly toxic plants from the Poison Garden can also be found outside. Smith explains that many poisonous plant species grow wild in the UK.

Some plants, such as the popular rhododendron, are grown in homes and also contain strong toxins like grayanotoxin. Another example is the common laburnum, a beautiful tree whose flowers and seeds are rich in cytisine. "The tree is so poisonous that if one of the branches was to fall to the floor, lay there for several months and the dog later comes along, picks it up to hold as a stick on a walk, chances are the dog won't finish the walk. It's that poisonous," he explained.

However, you don’t need to touch the plants to be in danger. For some, merely being near them, such as during pruning, can put you at risk. For example, the leaves of cherry laurel contain cyanogenic glycosides, which release cyanide ions.

Smith explains that these glycosides pose no threat to humans on their own. However, when the leaves are crushed, they release hydrogen cyanide. He adds that while the risk is negligible in open air, it becomes greater if the leaves are kept in a confined space or burned.

Inhaling hydrogen cyanide is lethal. The question then arises: how do garden staff protect themselves from these dangers? In an interview with BBC Travel, Robert Ternent, the head gardener at Alnwick, emphasises that safety is their priority. He adds that this can involve wearing gloves and, in some cases, full protective gear, including a suit, mask, and gloves.

The garden can only be visited with a guide. Entry to this extraordinary part of the complex costs £18.95 (approx CAD 34). Youths under 16 enter for free but must be accompanied by an adult. One adult can bring four children. The fifth and each subsequent child pays an entry fee of £6.60 (CAD 12). For safety reasons, entry with animals, except for guide dogs, is prohibited.

Remember that the Poison Garden is only part of the Alnwick complex, established in 1750. It also features the world’s largest treehouse, a cherry orchard, a serpentine garden, and many fountains. Tickets to the garden do not include the entry fee to Alnwick Castle.