It turns out I have a garden.
I moved in when there was still snow on the ground, and I only knew that there was a little patch of soil in my backyard from the few dead stems sticking out of the snow canopy. Eventually the snow melted, then spring came and passed, but the soil remained barren and dry. Summer started, and Trolley noticed some sprouting when he would go to smoke outside. He pulled some dead growth and weeds but did nothing more, not even a watering. The garden just started to bloom by itself.
I have no idea what kind of plants they are, but they seem to be doing well.