In article ,
Jills? wrote:

Get a CD of Bach and set the volume sufficiently loud enough for
their listening pleasure.

I was going to suggest something similar. There was a news story some
time ago about a convenience store owner whose business had become a
hangout for dopers and dealers and other n'eer-do-wells--a consequence
of both his location and his decision to sell liquor. The cops were at
best a very temporary solution, if they showed up at all.

This guy got the idea of playing classical music through cheap
loudspeakers mounted on the roof of his building. Whenever the groups
gathered in the area, he would put on some of his favorites--Beethoven,
Bach, Mozart, Tchaikovsky, Bizet, Wagner, ballet, opera, choral
music--even monastic chants BIG GRIN. He would play it just loudly
enough to be heard above the ambient street noise, conversation, and
any boomboxes the undesirables happened to have brought along.

Incredibly, it worked wonderfully! When interviewed the owner couldn't
have been happier with the results. It took less than a single week to
completely clear the thugs from the area, all on their own power. Last
I heard, he was planning on letting other store owners in bad parts of
town know about what great success he obtained with this method.

Perhaps this would work for the OP, but even if it didn't, I bet the
plants in the garden would love it.