It doesn't take much, at this time of year, for a plant to start growing. A scrap of soil, a pinch of dirt, a seed, and then trees are growing on downpipes and Herb Robert is growing absolutely everywhere.
The same is happening in my garden, and here and there a weed is growing so vigorously it's killing my favoured, loved, purchased plants, I try and take a philosophical view (after all, most weeds have flowers too, and the bees don't care) but it's actually infuriating to watch a border revert to an Alkanet monoculture, or Mediterranean herbs collapsing as their pots come under the demands of Marguerites and Willowherbs.
De-weeding a pot is a bit of a trial. I often end up knocking the plant out of the pot altogether and disentangling the roots, pinching out vine weevils as I go, replanting with freshened compost.
It's probably a terrible shock to their system.