Near the bridge connecting the medicinal plant collection with the Arboretum of the 40th Parallel North, on the lower terraces of both collections, a small collection of toxic plants is displayed.

Toxic plants have been used by humans since Prehistory. Some contain truly dangerous substances, which can have lethal effects if misused. The production of toxic compounds in plant tissues is an adaptive response to their environment, serving to deter herbivores or inhibit the germination of nearby plants (allelopathy).

Species found here include hemlock (Conium maculatum), oleander (Nerium oleander), chinaberry (Melia azedarach), privet (Ligustrum vulgare), squirting cucumber (Ecballium elaterium), cotoneaster (Cotoneaster lacteus) and yew (Taxus baccata).