The world is weird and I bet you could get in trouble. But I suspect that in general the worst that would happen is you would just be told to stop and/or made to remove the plants. That is purely an opinion though.
Wildflowers are nice, and should do OK if they’re ingenious to the area. But if you can devote some time to the project, how about planting strawberries? Or garlic? Or tomatoes? Different plants in different plots, as you say.
I doubt that a jury would convict you.
My neighbours did this two years ago with 3 or 4 of the rectangular dirt plots that surround the trees on our street. They planted some lovely flowers, and put up adorable miniature wooden fences painting in bright colours. The plots are public property, but they sent letters to the residents in the buildings to see if anyone minded, and it seemed no one did.
The problem was in the winter; the snow removal process in Montreal is kind of aggressive, with big plows (and the little zippy ones) just indiscriminately driving down the sidewalks and roads and moving the snow to where it can get picked up and carried away. This resulted in the little fences being torn to shreds, since they couldn’t be seen or avoided under 2 feet of snow! It made a mess of pretty-coloured shards or wood. The plows tend to bowl over forgotten bikes as well, leaving twisted lumps of metal behind.
I don’t think the neighbours tried again last year, but some flowers must have been annuals and re-grew. Looking out there now, there’s one green shoot of something popping up, but not much else. I’d love for them to plant flowers again, even if they don’t put fences back up!
So? Did you do it?
Internet access isn’t allowed in jail.
OK. I did one! Or rather two, but this one has blossomed the best ( the other one has zinnias only and they haven’t come in yet).
PRIDE!!!
Yay you!
That thank you sign is so sweet! There’s something really heartwarming about anonymous good deeds rewarded with anonymous thanks.
That’s wonderful! We don’t tend to realize how much other people notice and appreciate - I learned about this from working on my front yard, and getting comments from neighbours walking by all the time.
You go, you gardening guerilla, you! 
(I have a neighbour with a completely bare, terraced front yard. I’m DYING to plant that shit up.)
In theory, I suppose you could possibly be charged with trespassing, vandalism, malicious mischief, disturbing the peace, or some other similar crime. In practice, I would not expect anything like that to happen. You haven’t done any damage, and arguably, you made the world a better place.
From a law school hypothetical point of view, assuming the plots are private property and not owned by any political subdivision of the state, I wonder if possibly you could have begun to establish a claim for adverse possession?
Most satisfying personal dilemma dope thread in months! I’m picturing a kid’s book. Just beautiful as the original, but retooled, updated and retitled miss monstro.
How soon after the plot was planted did the sign appear? Who put it there?
Nice one. Any idea who put the sign up? That must have made you feel great.
I love it. I like the border as well - a neighbor has a picket fence that consists of varied-height/width weathered planks, and it’s gorgeous. Yours sort of reminds me of that. Where’d you get the wildflowers? Our local Nature Conservancy sells packets of indigenous flowering plant seeds for $1.50 every year.
That’s great. Nice work, Monstro.
?! I know you’re not saying it’s going to happen, but how can a bunch of flowers be construed as disturbing the peace?
And yes, the Thank You sign is made of warm fuzzies.
Well done you! That sign actually made me a bit teary
Those statutes are sometimes broad enough that they can cover situations where there’s not really anything else to charge somebody with, but the cops want to charge something…
“I was having such a lovely, peaceful day, and then all these goddamn flowers…”