The skull outside the entrance to Alnwick Garden in Northumberland isn’t just decorative. Many plants in these beds could actually kill. Foxgloves, snow-on-the-mountain, cow bell (left): over a hundred dangerous plants grow in this garden, laid out by Jane Percy, Duchess of Northumberland. The most toxic plant grown there is deadly nightshade. For children, just three of its jet-black berries (and, for adults, ten) could lead to a painful death.