I think this is the best thread to ask, since it literally has "raised beds" in the title. But, to the mods; Please feel free to move it if you deem necessary.
My wife and I have a picnic table which we never use. It's just not conducive to our current arrangement. We reside on the second floor of a 4 unit farmhouse. A few days ago I was looking at it out the window and had an idea I think is really viable. Since we've been planning our first garden, but can't dig up any of the rental property; Why not use the picnic table? I'm thinking about getting some pressure treated lumber to build raised beds right on the table. Veggies on the main portion, and flowers on the seating portions. Each box will be 4 boards with an inch or so of raised footing, and a few slats running under them. I've already got a localcoffee house that's going to give me some of their would-be-trash burlap bags to line the beds for drainage!
Ideally I'd like it to be mobile. The yard is at a funky angle, but there is good sun exposure. We're not in charge of the lawn mowing so I want us to be able to move it quickly and efficiently when we know the landlord is cutting. I'm thinking about fitting the legs with a frame all the way around, then fitting it with large casters. It doesn't have to move super easy, but just be able to move. With the dirt, would this be possible? I'm also slightly concerned about springtime/post rain ground conditions. But then I thought, perhaps some sort of rail system? Nothing insane, just a couple pieces of metal that the wheels could glide over. Kind of like going off-roading and having some diamond plate sheets to get you out of the mud.
Worth trying, or a disaster in the making? I can draw up a little diagram if this isn't making sense
I wouldn't use pressure treated wood. You will need to re-enforce the whole thing before you start filling with soil. I would use a .33 mix ratio of dirt, compost, perhaps vermiculite to keep it as light as possible while still being able to grow the things you want. For mobility, I would look into 10" tires with a wide tread, Harbor Freight has them pretty cheep, I would also think about using two per side on the axles so you have less compaction where you move it around or let it sit. My wife is having me build her a raised bed bench this spring. I'll be using 4x4 legs and under rim. the sides will be 2x10 or 2x12 untreated pine. I plan on using 2x10's for the floor with a sheet of mulch cloth over the floor and up the sides, to keep the soil from washing through the cracks, this will allow the soil to drain well but not go away.
I think you should discuss with the landlord leaving the table in one place and caring for the grass that grows around it yourself. Perhaps ask him if you could rock the small area the table us at. Moving it, with all that dirt, too heavy and unstable, imo.