can you not line the side against the wood with some sort of protective layer? Tyvek or something? And the fill with dirt and plant away :)

I agree with Gray, you could line the inside with a waterproof barrier and replant. Or, you could try your idea again. You could stack bricks or cinder blocks (or some other item) inside to help support the board. As long as you stacked them to the right height, they wouldn't show. It's a cute feature, I'd find a way to use it, rather than tear it out.

If you want to use it as a planter you'll need to remove the wood siding and sheating behind the planter, install cement board as your new sheathing and flash where the former siding was once located. Provide drainage at the bottom of the planter.

Do not fill the planter with soil. I recommend doing containters within this planter which will allow air along that wall that once held the siding. Containers will also allow you to check that wall for any moisture problems by removing them from the planter.

Good luck.

Line it, or find some large planters that fit inside it -- once they are filled with flowers & leafy plants you will never know the difference.

Your inspector was right, that's inviting in moisture and termites.
You could try lining the inside to keep the moisture out but I'd be afraid that moisture will still build up behind it.
I like your idea with the wood board. How about adding some support to keep the board from bowing? A few clay pots turned upside down might do the trick. Or you could build a platform but make it a little lower than the top of the planter, so it looks more built in.

I would just plunk some potted plants in there.

I would find long planter box to put in there. Or wall off the back with a board, so there is a few inches between it and the siding. Then fill it back up and plant away!

or you put big pots into it and plant them … with something that is bushy enough to hide the fact that there are pots to begin with.

Assuming there are no drainage issues that would affect the siding, why not just fill it with large plants in plastic planters (bushy enough so you wouldn't see the planters.) Or perhaps you could improvise your own planters by drilling holes in the bottoms of large containers (like those Rubbermaid storage tubs.)

Rotting siding is a bad sign. I recommend that you remove the siding and sheathing underneath (probably also rotting). Install cement board and flash over that board so that water drains to the bottom of the planter. You'll need to provide a drain at the bottom of the planter if there isn't one.

Next, avoid putting any soil against your house regardless of the quality of the flashing. I recommend doing container plants inside the existing planter to allow air to flow against the wall of your house and to allow you to maintain that wall without having to dig out soil.

Big potted plants, in a row. Lavender, say. It'll look great, and it's doubtful anyone will even notice that the pots are inside a planter.

What if you built a back to the brick box with a gap so it is a few inches away from the house? If it's stand-alone, you can fill it with dirt and plants to your heart's content. Even better (but way more heavy lifting) would be to shift the whole thing out a few inches so the brick isn't touching the siding at all. Then you still have the visual effect but no contact with the house so no damage.

Duane beat me to it! If the previous owner had wet soil piled up against the wood it's probably best to pull it out no matter what. Damage has already been done. As long as you're at it you may as well make it Hardie board and use the thing as a real planter.

You could just put some big pots in the space.
Or use another piece of wood with some supports underneath.

It looks to me as though the brick is actually built up over the boards. So there's no simple pulling them down and replacing with cement board- without knocking out brick. I think if the wood has had some time to dry- poke it with a screwdriver. If it's still solid, seal it up and protect it with some kind of wood sealant. Then perhaps you could install cement board over it, seal the corners, and use as a planter- or devise a planter that fits inside but doesn't touch the back.

Go back to your plants-on-a-board idea. Just fill most of the planter with something that will support the board without harming the siding. This could be a couple of plastic bins (hidden storage!), or empty plastic milk jugs with the tops on (reusing before recycling!), stacks of plastic flowerpots, or some combination thereof. Then lay your board on top and arrange your annuals in pots or other little planters. Unlike with a window box or other places where the plants are really planted, you get the advantage of being able to show off whatever's blooming by moving it to the front. Then when it fades, there's no trouble is moving it to the back. Maximum payoff from the plants you choose.

If you want to put a board on top, attach 2 2x4's on edge (ie with the 4" side vertical) on the underside of the board with 8-12 screws. They do not have to go the whole length, maybe stop 12" from each end. This will make the board into a beam by stiffening it and it will not bow. Better than attaching 'legs' towards an uneven surface below.

Bench? With pavers in front? This may or may not look "right" depending on what is nearby.

I like the idea of turning it into a bench and utilizing the space beneath for gardening storage

I can see that as a completely edible garden - everything growing in tubs.

I highly recommend not to use a waterproof lining as others have suggested. Though a good short-term solution, water and moisture will eventually find its way behind the lining and could even expedite the moisture problem with the wood siding.

Other ideas such as reinforced board for small planters or deep, large planters should be safe.

If a bench, make sure to use a flashing against the siding.

Depending on the damage already done to the siding, it may be smart to replace them

I would steer away from introducing water. If this is located in the back of the home, I would suggest building a propane type fire feature. It would be nice with a built out paver patio in front of it.

If its in the front of the house (from your description I believe it is) tear it out. Paint the boards to match the house color and plant a small flowering fruit tree in the center surrounded by low grasses or shrubs.

I'm with mhurleygirl, a bench with storage for garden tools, that's what i would do. :)

put pots inside the planter that way you can have plants in it but the dirt wont be near the wood!

We just tore one like that out a couple of months ago, and it looks great (I didn't think it would). I'm not sure where you live, but in Northern California, almost anything you do with these planters (cement board, potted plants, etc.) is a recipe for thousands of dollars in dry rot in a few years. Sorry to be negative, they are cute! But after just having spent $10K on dry rot repairs, I won't ever have plants right next to wood siding again,...

If you want to keep it, you can fill the bottom with styrofoam peanuts & then check out your local area for a recycled glass mulch. Put down some screening material or landscape fabric overs the peanuts. Then fill with a few inches of the glass mulch, or cool looking stones, and then throw 3-5 pots on top of that with unobtrusive plastic dishes underneath the pots to catch any water after you hand water your plants. Or skip plants and find something cool that works with the rock or glass mulch. I know this sounds cheesy, but I regulalry see a planter with glass mulch, stones placed in a swirl pattern, and then a terracotta fish pot in the middle of the swirl. It looks like a fish coming out of the ocean. It is very whimsical and my kids love it.

You can fix the siding and/or tear it out, too, but if you need to keep it for a while or need to prioritize other projects, this approach can work.

mini zen garden?

You could imply a fountain using no water by putting a shallow tray with interesting smooth zen-like river rocks in the top of the brick thing, then the type of flat gargoyle sculpture that usually spits water into a small pool could go right above it. Maybe a few succulents in the rocks.

I think I'd play it safe and take it out.
If not, you could use concrete block or something similar to prop up the middle and just have a bench. In Winter and or Spring you could put glass or plastic over the top and have a cold frame. I know the top is supposed to be slanted but my first one wasn't. I cut back my potted fuschias and wintered them in it. You could also use it for hardening off annuals.

I would demolish the planter completely and plant directly into the ground. This planter was not designed properly and will just continue to cause problems no mater what you do.

I would have to agree with mhurleygirl, I would try to make it into a bench of some kind. If that doesn't fit into your design plan, then I agree with redbellybutton, demolish it and use the newly gained square footage to design an really nice flower bed filled with edibles!

Is it big enough for a day bed?? platform either on top of the existing planter or sunk down in. Attach a mosquito net or canapy to the side of the house.

Or get a feed tub or small molded pond liner that fits in and attach a wall fountin to the side of the house. Use small planter boxes around the front to camouflage.

Depending on how deep the planter is, you could stack bricks to allow pots to look like they were planted in there but they would still be in pots. I would recommend ivy types up front, a splash of color in the middle and back and I see there is a spot for a vine in the back. Once it is grown in the planter would look as if you did plant them inside it instead of the pots they are in.

Good Luck!

Thanks for the comments, everyone! We're focusing on a massive backyard redesign right now so though we may eventually demolish it, we'll be keeping it for awhile. We had talked about the idea of a bench briefly but after reading all these comments, we may just do that. This is the very front of our house looking out over our gorgeous front yard. I also really liked the cold frame idea. Maybe we can make it a multi-use zone. Eventually, we will repair and reside which will take care of any previous damage and prevent further rot issues.