A few years ago I planted some borage in my garden. The bees loved it. I also noticed that in my area, borage will readily self-seed and spread like a weed. I had borage plants popping up all over my property, neighbors' property, etc.
Now I'm walking to the grocery store and looking around at every plant I see, evaluating its usefulness to bees, and I'm noticing countless little niches and pathways and public spaces where weeds grow anyway, that I could toss some borage seeds down on my walk, and they'd sprout, grow, feed the bees, reseed, spread and feed the bees again - all on their own. No one will probably even notice as these areas are barely tended/not tended anyway.
So I ordered a 1/4lb. bag of borage seed that I intend to spread around my surrounding blocks this year, and in a couple years, the neighborhood should have a feral, self-sustaining population of wild borage feeding the local bee population.