We owe it to each other to share our horror stories, as well as our successes!
How's the Pratia?
Well behaved? (above). Not! (below)
Pratia pedunculata, also known as Blue Star Creeper, is an attractive plant at first sight, with small sky-blue starry flowers in great profusion above a mat of dark-green foliage (top photo), so some years ago when I first encountered it in Harry Byrne's Garden Centre I bought it for my new rock garden. Perhaps you've considered doing the same? Don't.
It thrived in my garden, unlike many of my initial purchases, so when my father came visiting from New Zealand later that year, I prepared proudly to show it off. If I expected admiration, I was disappointed. As his gaze wandered over the plants he suddenly let out a cry of horror: "What's that?!!!". Unsure what should cause such concern I simply replied "Pratia". "Get it out" he immediately responded, "Get it out now!!". He wouldn't take no for an answer so, then being a few decades past the age when I thought my father a complete fool, I agreed, though with reluctance. As we went to get a fork, he explained.
A couple of years before he too had bought a plant for his rock garden, on the slopes of the Port Hills overlooking Christchurch. It too had flourished and expanded until, too late, he realised it was invading other plants. Attempts to get rid of it had failed. So we dug my plant up, noted the creeping underground stolons, reassured ourselves there was none left, and moved it to a safe location between stones in the patio below the rock garden.
On both counts we were wrong. Some weeks later I noticed the familiar flowers back in the rock garden, so hastily removed the rogue plant, and it has not returned. But the piece in the patio flourished and gradually over the years made its slow, unnoticed way upwards towards the rock garden behind the retaining sleepers.
Meanwhile no phone call home to New Zealand was complete without the concerned question "How's the Pratia?". Wars of increasing severity had been fought and lost. The invader had now reached several metres from its original spot (see lower picture), easily finding its way under a stone path. My father was now worried that any instance of Pratia represented a threat to me and when he returned last summer he investigated my plant thoroughly and pointed out (did I detect a note of schadenfreude?) the signs of imminent invasion. Quickly we fetched the Roundup and doused the Pratia liberally. It has apparently succumbed, though I won't rest easy until another season has passed.
We looked up the entry for Pratia pedunculata in the RHS Encyclopedia of Garden Plants. It says 'Height: 1.5cm, Spread: Indefinite'.
I rest my case.