I'm not happy with the underneath of the planters, the gravel then a gap then the box looks messy. What about planting wee creepy things () -ground hugging stuff - along there to soften that line? Or would it be easier just plonking down window box type planters with stuff in them?
You could have a ground cover plant like waldstenia ternata, though it would take a while to creep round. Or some little carex grasses that only grow to 6" tall and gradually bulk out would be fine. If you leave it, doubtless things will seed themselves in the gravel, unless you have laid membrane, so you could just wait and see what arrives. Or if it is very sunny and hot, little eryngion daisies would be happy.
The important thing is that you’ve got the planters level @fumanchu! The blue planter behind also has a gap, they all look fine to me!
There is membrane under there and under the membrane there is more gravel.. It is south/west facing and gets very hot in summer, but it's Scotland and sun is never guaranteed. I think maybe I'm being too nitpicky - but viewed from the pavement that gap hits me in the eye and bugs me. But I think maybe anything else might be overdoing it. Unless I go for plastic flowers stuck into the damn gravel
Plenty of options. Here's some ideas. Nice cobble stones around the bottom edges. Nice plant pots with some sort of feathery plants or ferns to soften the hard lines. Or, something trailing planted in the raised beds to trail down the sides. Or some combination of the above. It depends on your personal preference of course.
The planters look like they have come with small feet to keep the planters raised off the floor when used on hard standing ground. As your area is covered with gravel with gravel under the membrane then I assume you don't have an issue with standing water. I personally would of unscrewed the legs and let the planters sit flush on the gravel before filling them.
Just add more gravel. Plastic plants would be absolutely hideous IMO. My raised beds [built in rather than free standing] are all in contact with the gravel around them - similar to what @gks describes. I do have some small plants at the foot of some, and some of those are self seeded.
How about something like Veronica Georgia which is lovely evergreen ground cover with little blue flowers in spring? That would fit in well with the raised planting. It likes sun and is very undemanding, easily trimmed to the shape and space you want.
Veronicas [especially the taller types] aren't generally great here unless the soil is really well amended, or, for those spreading low growing plants, the gravel is thick enough that they aren't getting much contact with what's lower down. Too cold and wet for them, long term, although @fumanchu 's site might be drier and better draining than where I am. I grow various things in the gravel, but they're basically sitting on top of it, and there has to be something light lower down for them to root into or they can't manage
I was thinking of Georgia which, down here, only gets to an inch or so off the ground and loves growing in gravel and poorer soil as long as it is not bone dry. It would depend how thick the gravel was, of course. Mine is just a top dressing, not a quarry!
***************************************************************************************** If I could get my paws on wee decorative paving slabs then I'd use them, but unsure where to get, with being housebound and non driver. I have ordered 5 bare roots of Saponaria to drip over the edge and take the eye off the gap though.
***************************************************************************************** Not feet gks, they are crossbars/spars that are fixed to the boxes. My son put them in place and I wish he had taken more time about it but saying nowt or he'll never help again