Here's a brass-look bed headboard/bed frame I got on Facebook for $5. I brought it home and removed all the extraneous bolts, caps, etc. The wrought Iron style I was hoping to find were going for $200 locally, so I passed and went with this.
A Permanent Flower 'bed' for My Backyard
A quick concrete technique that's easy to do for lightweight stuff
I found a spot along the fence where it would fit and measured the width of the posts. I threw a bit of black bbq grill paint on it to see what would happen. I wasn't happy with the results, but the look is still ok. The dark paint will help the flowers pop.
I dug two shallow holes for the legs 8" or so, and then cut away the sod in front of it. My goal is to have varying heights of flowers front-to-back (foot to head?) and so I started in the 'back'.
I dropped the headboard frame into my holes. I had a leftover bag of $7 mortar from another project, so I poured dry mortar into the hole, only filling about 1" or so. I always wear gloves around this stuff.
Add water slowly until it's completely wet. Repeat with 1" of dry mortar and water, again and again until you reach the level you want. You could use concrete, mix, or concrete/sand blend, or whatever you have around.
I sturdied the headboard frame overnight with a scrap 2x4 so it would remain vertical/plumb until the mortar hardened.
Here's the left side hardened the next day. This isn't fence-strong by any means, but will hold my ornamental display for years to come, and should I ever sell the place it will be easy to remove.
I got some seeds off ebay cheap, and thought I'd try growing from scratch. I threw down some topsoil, a handful of seeds, more topsoil, and a bit of red mulch to keep the rain from disturbing the seeds.
Here's the flower bed along side my chainlink fence. Eight weeks later the Celosia are about 30" tall, and just starting to bloom. I placed a few bedding plants along the side. I hope you approve