Large planter box on concrete

[rachspin]

I've searched around the internet a bit, and I've found some helpful information about planting grass on top of concrete, but I'm still in need of a little "expert" advice.

We recently bought a house with no yard. We have a side patio area that is fenced in, but it is 100% concrete. It runs the length of the house, and the concrete appears to be connected to (or part of) the concrete slab foundation for the house. The concrete itself is about 4 inches thick and has drains installed that may or may not be tied in to the sewer (?). We desperately miss having a yard, and my dog sincerely misses his grass. Our thought is to build a large planter box to cover the concrete. It's sectioned into 4 large square pads, and we would like to cover 2 of them. I've read about what kind of layering we need to do with soil and organic matter to keep the grass healthy, but what I can't find is how to construct the "box".

We're talking about nearly 6" of dirt/organic matter/grass, which I assume gets pretty heavy and would put a lot of pressure on the sides of the planter. I'm guessing we will need to drill some holes into the concrete to secure the box somehow? Should we even be considering using wood or should we be thinking more along the lines of stones, rocks, bricks?

My next step is to get a quote from a landscaper about removing the 2 sections of concrete, but I'm concerned about the connection to the foundation of the house. Removing it may not be an option. Any advice, help, ideas will be greatly appreciated!

[rainbowgardener]

I had a similar situation, the only flat, reasonably sunny area in my yard was covered with concrete patio. I looked into having it removed, but it would have been really expensive and the ground under it would be totally dead.

So I built raised bed boxes on top of it like this:

https://www.helpfulgardener.com/forum/viewtopic.php?p=105961&highlight=raised+beds#105961

They are starting their 9th season now and have held up really well. I grow tomatoes and peppers and anything I want in them. If you read that thread, it tells how they are constructed. Trick in building them on concrete is to make them deep enough. And then you will have to have a considerable amount of topsoil trucked in for them. If I'm remembering right, each of my 8x4' boxes took a cubic yard of soil to fill.

Incidentally, as it says in the original thread, that was a plain grey concrete slab. Before I put the boxes on it, I hired someone to come in with a big concrete cutter and cut the lines in it to divide it in big squares and then I stained it terra cotta colored. It gives it the look of terra cotta pavers at way less expense. Everyone tells me it is beautiful. It is really nice to have a hit of color in your garden through the winter. We do have to renew the concrete stain every 2-3 years (not under the boxes though, once those are built and filled, they do NOT move!).

[Bobberman]

How big a area are you wanting to cover. I have several suggestions out of the ordinary! I have had sidewalks that were completely covered with weeds and grass just because of dirt washed over it throuh the years. Indoor Outdoor grass may be a option. I have covered many patios with it since I am in the carpet business. I would also suggest that you find a old used carpet the size you want to cover let say a 9 by 12 area and lay it down upside down with the back showing put some compost or just regular top soil over it several inches. By grass that they sell by the square foot and lay it over the area and it will grow great since the carpet will hold the moisture!. Several layers of cardboard over the concrete first will also work but carpet seems to hold the roots better! Most carpets have a jute or burap back which will rot over a 5 to 10 year period!I have done this many times! Any carpet dealer will have old carpet in their dumpster. The old jute pad called hair pad will also work as a base. You could even use land scape timbers for your border or even some nice border type brick! The nice thing about your situation is the nice flat area you a re covering! If you ever get tired of the grass or want to make it smaller its easy! I also failed to mention that the carpet stops the soil from being washed away by the heavy rains! Another option is medium gravel covered with dirt then the grass!

[rachspin]

Both of you have great suggestions! Thank you!

Bobberman, I had not heard the carpet idea, but I'm going to look into that some more. We actually have a large piece of old spare carpet in our garage, so that is totally do-able. We don't want to use outdoor carpet to cover it, because our dog would ruin it. He will use the bathroom on ANYTHING and if it's real grass, it doesn't matter!

Rainbowgardener, I love the look of your planter boxes. I saw that you said you drilled holes straight down in the wood and then inserted rebar. Did you go all the way into the concrete with the rebar, or just through the wood? How is the wood holding up? Have you had any issues with it rotting? You said that you restain them every few years, so I assume that helps? I love the idea of cutting and staining the concrete. We live in a pretty cookie-cutter neighborhood and something like that would make our house really stand out when we sell it in a few years!

We haven't measured the patio but it's probably 10 feet wide and we're looking to do about 20 feet long for the planter. We have to do a little creative cornering around our HVAC unit since it's installed on the slab, but I don't think that will be an issue since we'll just leave a few inches around it on each side.

Thanks again to both of you for the great ideas! I'm getting excited about getting out there this spring and making our patio look great!

[rainbowgardener]

Just went through the wood with the rebar, not into the concrete. They are not attached to the concrete in any way, but since they are full of dirt, it doesn't matter; they aren't going anywhere! You don't want to seal it at the bottom, since you want excess water to seep out.

The wood is holding up very well. Very little deterioration. I do re-seal the outside every couple years or so (along with re-doing the concrete stain).

[DustonMcGroarty]

I'm gonna throw this out there out of concern...

I would at least get a quote to have the slab removed. Eventually your wooden planter box will rot (even treated wood will rot especially after soaking up moisture from the dirt contained in it).

Also, what happens if your slab cracks and one piece shifts up higher than the other? It will be a huge pain to have to remove your box to take care of it.

Not trying to be negative, I just wanted to point out a few things that concerned me when reading this. I always put myself in the situation as if it were my own.

Hopefully you can get it worked out!

[rainbowgardener]

I did get a quote re having mine removed and it was a couple thousand dollars. If you did that, the ground under it would be totally compacted and dead, so you would still have to build raised beds. My wooden boxes have been sitting there for 9 years and are going strong. I did seal them before I filled them and re-seal the outsides every couple years, but of course can't get to the insides any more. They are 4x4 fence posts; boards would not last nearly as long. Our concrete has some cracks which we fill, but it hasn't heaved or tilted or anything.

[Bobberman]

At least the slabs are level. I would go with raised beds all over the slabs You can use anything in between to walk on! A cheap piece of indoor outdoor capret glued to the slabs would last for years. I have put the thin indoor outdoor on minuture golf courses on slabs and they lasted for years! They make a real thin indoor utdoor that looks like felt and is only about $3 a square yard I would recomend that and glue it down.They call it sometimes needle bond indoor outdoor! Ozite company originall made it! Don't use the indoor outdoor grass it will holld too much dirt. The thin stuff can be sprayed off with a hose. I did a arobics place this past year over a slab and he likes it so much that this is the third area I covered for him! It even comes in a bunch of paterns!! The have a off greeen that is nice! Lowes carries it. It looks thin and cheap buy it wears like iron!