If it has not occurred to you to ask permission to garden in your neighbour's yard before, I say what have you got to lose? All they can say is "no". If you can see it, consider planting it and if you are able to afford it offer to contribute the plants themselves.
In this case the vacant tree ring turned garden bed is behind our bench, which is a focal point, so I wanted to adopt it.
With our late spring this year the early-blooming "Ice Follies" daffodils are just now blooming and they look smashing. Next year I hope to see them blooming before the daylilies get so big, but this year I am just happy to see them at all. "Pink Pride" daffs, randomly and equally mixed with the Ice Follies, will bloom after the latter are done.
Last fall I detailed this guerrilla gardening episode in my neighbour's front yard. Not the first time I had gardened in a neighbor's yard, but the first time without permission.
It will be interesting to see if the daylilies get enough sun for any blooms.
I will keep you posted.