Here's a backward question. At my apartment complex, there are long
stretches of flower beds where the only thing growing is the usual generic
evergreens. I have not seen a single plant growing there since the ground
thawed in April. I know for a fact that nobody's doing any weeding, but I
*do* know that last September, some ancient man was walking around with a
tank & sprayer, hosing down all the bare spots. Even so, I'd expect
SOMETHING to pop up almost a year later. He had no idea what he was
applying - "They just told me to spray what was in the tank".

This is just curiosity on my part, but what could he have applied that would
kill everything for such a long time? By the way, there's no weed barrier in
these beds - it's about 25% covered with some faded wood chips, but that's
all.