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Marin IJ Articles

Ivy: super thug in the garden

  • Diane Lynch
  • 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 (H. canariensis), and Cape (Delairea odorata) in particular.

    This mature ivy has produced a bumper crop of seeds ready to be planted. Photo: Diane Lynch
    This mature ivy has produced a bumper crop of seeds ready to be planted. Photo: Diane Lynch
    Cape ivy is native to South Africa, where its range is relatively small, growing in moist mountain forests. It was introduced to the eastern US in the 1850s as a cute little house plant 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 currently covers an astounding 500,000 acres in California alone. In 1987 there were 9 acres in the Marin Headlands; within a decade, that area was up to 67 acres. In 2015 Point Reyes National Seashore and Golden Gate National Park started working to remove 188 acres. The follow-up to remove new shoots goes on for several years. Pieces as small as 1/2” 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.

    This patch of variegated ivy is kept small and not allowed to escape to the rest of the garden. Photo: Diane Lynch
    This patch of variegated ivy is kept small and not allowed to escape to the rest of the garden. Photo: Diane Lynch
    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’x4’ 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. But the good news is that there are better choices for ground covers that won’t attract and harbor rats. Master Gardener Marie Narlock had an article in the IJ on April 30 that explains some alternative plants that can replace a lawn, some of which could also work as replacements for ivy. See https://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.