While birds may leave English ivy until there’s almost nothing else left, humans adore it.  We plant it in the yard, hang it on the porch, train it up the wall, pot it up in the house, reproduce it on the wallpaper, and dedicate “coffee table” picture books to it.   We’ve created a stunning array of hybrids, all of which seem to be available at the grocery for a tempting $3.50.  Bet you can’t buy just one. (I confess to 10.)

Unfortunately, the birds do like the berries of this European member of the ginseng family enough to get Hedera helix on the invasive species list as an aggressive tree killer that creates “ivy deserts” barren of all other plant life.  Two fellow immigrants, the English sparrow and the European starling, are the chief culprits, abetted by robins and cedar waxwings.

And you’re probably still thinking: ” Ivy has berries?”   Yes, with a few years’ patience and a whole lot of sun, you get whitish flowers in fall then dark blue berries in late winter.  Pretty but poisonous to humans and the environment, so if you must grow ivy outdoors, stay in the shade.

The really interesting thing about ivy, though, is a sneaky biological switch that creates “tree ivy”.   English ivy starts as a woody-stemmed vine that crawls all over and then runs up the first tree it finds.  But sooner or later it runs out of tree-support.  Then a mysterious thing happens: the ivy’s genes change to produce new stiff-stemmed branches that can support themselves (as is in the picture).  Now here’s the coolest part: once ivy changes its genes, it can’t change back.  Root a tree ivy cutting and get a little ivy-leafed tree.

I’ve never seen the Hedera hybrids bear flowers or morph into tree ivy.  I don’t know if they can’t or if they just don’t get the opportunity.

Even though English ivy has been kept as a houseplant for centuries, it becomes a spider mite magnet in the hot, desert-dry atmosphere of the modern centrally-heated house.  Keep it happy with weekly cold water baths (make sure to wash under the leaves).   Alternatively, it does well in a high-humidity tropical terrarium.