Q: This weed has probably got into my garden from a pot plant. I can’t identify it and what’s worse, I can’t kill it! The coin is a €1 piece. The weed forms mats and I’ve tried several different proprietary weedkillers to no avail. Please advise. If I do have to dig it out it will be very difficult as it is so small, bits of it are easily left behind. PD
A: Judging by your description and photograph, this looks like Soleirolia soleirolii, or “mind your own business” (something that this very pretty but somewhat invasive plant definitely doesn’t do). A member of the nettle family, it’s a non-native plant that hails from Corsica and Sardinia, and was probably first introduced to Ireland back in the Victorian era as a greenhouse plant before escaping out into the wild. Its Latin name is derived from the 19th-century French engineer and botanist Joseph-Francois Soleirol, who was believed to be the first to collect it as a living plant specimen (in fact it was more likely his younger brother, Henri-Augustin, who did so).
I say “wild” but in fact this low-growing, mat-forming, evergreen perennial is more commonly found in cultivated gardens, growing in lawns, paving cracks and gaps in old stone walls where it readily finds a foothold and can quickly colonise large areas if left unchecked. Happiest in shade, but tolerant of a wide range of growing conditions, it’s generally found in coastal Irish gardens rather than cooler midland parts of the country, but is surprisingly hardy.
Some gardeners hate it with a vengeance and wage persistent war against it but usually to little avail. Resistant to most weedkillers, it spreads by seed as well as by very slender stems that send down roots as they creep along the ground. “Mind your own business” can even tolerate being mown, which is why it’s often found growing in shady lawns, sometimes to the point where it can start to suffocate grass growth. A pretty little plant covered with tiny pink flowers in summer, it’s easy enough to pull out but is capable of reshooting from even tiny fragments of the plant left in the ground.
Many Irish gardeners happily tolerate this dainty perennial growing in their plots, seeing its attractive growth habit and ability to soften the corners of hard paving elements as a plus. Its ability to grow in deep shade means that it’s also sometimes used as a substitute for a conventional lawn (grass struggles in deep shade) while it looks right at home in a Japanese-style garden. Despite its invasive tendencies, it’s also still sold in garden centres as a houseplant (it looks lovely in a terrarium).
Rather than resorting to using triclopyr, the one powerful but environmentally harmful selective systemic herbicide that is effective against it (you’d have to keep applying this repeatedly as a spot treatment to destroy young seedlings as they appear, risking damage to other plants growing nearby), my suggestion is to take the much easier, planet-friendly approach. This means reconciling yourself to the fact that this pretty, evergreen, resilient little plant has taken up residence in your garden, and exploiting and enjoying its many decorative qualities.