THUGS!

When the commune's gardening "experts" did a total remake of the herbaceous borders before the Hôtel de Ville, they brought in tens of tons of cheap & nasty top soil.

They planted out way  too many plants & shrubs - heathers, azaleas, roses - they're all under there somewhere. Unfortunately the cheap & nasty top soil came pre-loaded with clandestine thugs...

Horsetail & convolvulus among others...