Some suggestions to avoid it looking gaudy: make the planters as big as possible, make them all the same, in design if not in size, plant them up using a limited colour palette and repeat the plantings in more than one container.

And make sure they have bottoms! If they don't maple feeder roots may grow up into the planters.

lacey, I hear you on the feeder roots. That was one of my rookie mistakes when I moved here. I was thinking beautiful shade loving annuals around the maple. When I inspected the poor dying plants, it took all of my strength to pull them loose from the tentacle roots of the maple. Floral, thank you for awesome advice! Planters are going on sale now (end of season), so I will be able to get larger ones at a pretty good price. I feel better having a plan now with color and scale. As it is late in the season, they may get started with spring bulbs planted this fall. But I'm totally jazzed to have a plan brewing.

I had a planter with drainage holes under a maple, and one year when I went to plant it, I discovered that maple roots had grown all the way into the pot through the drainage holes and had filled the entire space. So either raise your planters up on feet of some kind (such as bricks) or place a saucer of some kind under each.

I agree with making the planters large and all the same, and I would use a low-key color that blends in well with the fence as a background. You don't want bright blue planters.

You will also want to choose hardier than usual plants since the planters get colder than the ground due to having less mass and being more exposed to the air than in-ground plants, and they will need to be frost-proof so they don't shatter during the winter. Usually the rule of thumb is choose plants 2 zones hardier than your area, though some plants won't follow that and will surprise you either by dying or being hardier than expected.