Invasive species: The damage they inflict on your garden


In a corner of our garden, we have a Dwarf Korean Lilac Standard that’s more than 10 years old. So, the crown is about eight feet across. Each year, in May, we are rewarded by tiny sprays of lilac flowers and their fragrance throughout the garden.

Under the tree, however, was a wasteland. It was a dark corner where nothing would grow. About four years ago, we planted a 10-pack of Creeping Jenny. It has taken a number of years for the Creeping Jenny to spread all under the Dwarf Korean Lilac Standard. In July, it was just beautiful: as the sun hit the Creeping Jenny, it provided a “pop” of acid green carpet under the lilac tree.

Then something awful happened. Over about a two week period, the tree started to dry up. You could take the leaves and they would crumble in your hand, like sage when you're making the stuffing at Thanksgiving.

With the Creeping Jenny now forming a solid carpet and covering the ground, the leaves of the Dwarf Korean Lilac Standard lost their glaucous coating and started to dry up. The leaves are still attached to the tree (they have not dropped), but it is as if the tree was freeze-dried. After doing some research, we discovered that the Creeping Jenny was what was causing our Dwarf Korean Lilac Standard to wither. The nature of invasive species is that they rob other plants and trees of water, oxygen, and nutrients in the soil.

An hour later, we dug up all the Creeping Jenny, roots and all. We put down a thick layer of compost, followed by two bags of topsoil. We watered it in well. We watered it a second time 48 hours later. The good news: the tree’s leaves have now absorbed some water and are not as brittle as before. The branches of the tree are still supple and don’t break. We may have acted at the 11th hour to save the tree. This story isn’t over yet; the key will be how the Dwarf Korean Lilac Standard will over-winter. And, will it leaf out in the spring?

Invasive species are a nuisance. One might ask why garden centres sell them at all. Creeping Jenny is a still a lovely looking plant and a good ground cover. But it just takes over all other plants. Do not under-plant large trees with Creeping Jenny, as this invasive species will rob even a mature tree of the water, oxygen, and nutrients it needs. And then you may end up paying an arborist thousands of dollars to have a mature tree removed.

#InvasivePlants

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