English ivy, Hedera helix, is probably the nastiest and most aggressively invasive exotic species that I work with. It climbs high into redwood trees and overwhelms understory plants (that live below the trees). It invades many of the landscapes, and worst of all, it climbs building where it ruins paint and causes rot. It grows faster than we can keep up with it.

English ivy is actually a nice ground cover plant for refined landscapes. I grew it at my home in town. Contrary to popular belief, it does not root into and parasitize the trees that it climbs. Actually, it rarely overwhelms and shades out large trees. It prefers to keep them alive for support, from which it disperses its seed. However, it does promote decay in the trunks that it climbs, particularly where it retains moisture at ground level. Native trees are not accustomed to that.

We…