The thing about vines is that they want to cover the world. With indeterminate growth, some will keep growing and sprouting side shoots until something — you — stops them. So, pay attention to those plant labels. Some of the worst are the ivies, English (Hedera helix), Algerian (Hedera canariensis) and Cape (Delairea odorata) in particular.
Cape ivy is native to South Africa, where its range is relatively small, growing in moist mountain forests. It was introduced to the eastern United States in the 1850s as a cute little houseplant with pretty yellow blooms. But it’s become a real problem along the entire West Coast, especially along stream banks, coastal forests and areas with a high water table. It covers an astounding 500,000 acres in California alone. In 1987, there were nine acres in the Marin Headlands; within a decade, that area was up to 67 acres. In 2015, the Point Reyes National Seashore and Golden Gate National Recreation Area started working to remove 188 acres. The follow-up to remove new shoots goes on for several years. Pieces as small as 1/2 inch with a node can sprout to produce more plants. Ugh!
English ivy, native to Europe, is still sold in nurseries, and it’s admittedly an attractive plant before it escapes and runs rampantly all over the neighborhood. It is fast growing, perennial and evergreen. It does best with some water all year round (is your irrigation system wasting water on it?) and favors some summer shade. It can grow 60 to 90 feet and form a dense mat that will outcompete just about everything in your garden and cover your shrubs, trees and house if not kept in check.
English ivy has two growth phases. The juvenile form has leaves with three to five lobes and adventitious roots along the stems that allow it to adhere as it climbs anything in its path. When it matures to the adult reproductive stage, the leaves will change to an oval/diamond shape, and the clinging roots will disappear as it becomes a tree. It will flower in the fall, which is unusual, and produce thousands of pea-size black seeds as it colonizes the area around it and beyond.
Algerian ivy looks similar to English ivy but is native to the Canary Islands. If it’s lucky and gets planted near a stream, it can grow to 50 meters, branching along the way. In theory, one start could cover a football field.
I admit to having a small patch of variegated ivy that’s dear to me because my late aunt took some cuttings from our garden in Italy in the 1950s. The patch on my fence is kept to about 4 feet by 4 feet and not allowed to escape out into the garden, so it doesn’t effectively shelter rats. But, in the 24 years I’ve had it there, it has yet to mature, bloom and seed.
Ivy has long been planted on hillsides to hold the soil. The task of removing it is certainly daunting and potentially expensive. Along with planting something else, one must be vigilant for several years and remove any sprouts that appear.
The good news is that there are better choices for ground covers that won’t attract and harbor rats. Master Gardener Marie Narlock’s IJ article in April that explains some alternative plants that can replace a lawn, some of which could also work as replacements for ivy. See plantmaster.com/presents/plants.php?id=5fa61113345df for ideas.
We live in a glorious place, with thousands of native and endemic plants in one of 25 unique biodiversity hotspots worldwide. Unfortunately, many non-native introduced species have invaded the wildlands in California. With our climate changing and likely getting drier, it’s a good time to consider planting more natives that will survive with less water over the long term and have less impact on our wildlands.
Sponsored by UC Cooperative Extension, the University of California Marin Master Gardeners provide science- and research-based information for home gardeners. Email questions to [email protected]. Attach photos for inquiries about plant pests or diseases. The office is closed for drop-in visits. Subscribe to the Leaflet, UC Marin Master Gardener’s free quarterly e-newsletter, at marinmg.ucanr.edu