Acer
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Planting Over Concrete

First post. Glad to be here.

I'm in the process of converting my backyard into a real garden. There is a spot that has some kind of concrete slab. I would like to plant over this and not break my back tearing it up.

I'm guessing the best option is to use raised beds. The idea of a raised berm doesn't really fit into the style I'm shootin' for.

I haven't decided what exactly I want to plant there, but I'm leaning toward a rose garden. How deep does the soil need to be? Is 12" enough for shrubs and roses? For the shrubs I'm considering boxwoods. What about a lilac? Do the roots of shrubs and perrenials grow outward or down? Would the limited depth affect their performance?

Another issue is drainage. Would I have to angle the bottom of the bed and provide weep holes?

I appreciate your answers to these questions, but feel free to give me other ideas, too.

John

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Grey
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Well, I'd be concerned with raised beds as far as drainage goes. You could do a bunch of huge planters, arrange them at the four corners of your slab, and set up your patio furniture in the middle.

Val can answer your question on how deep rose roots go - she's the rose expert around here. :) Shrubs would definitely need more than 12."

How big is this slab?

Acer
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The slab is about 8' x 8'. I forgot to mention it's a little below grade and has grass growing on top of it.

I've been thinking a lot about it and I'm considering planting a smaller tree....amur maple..... next to the slab, dump some dirt on the slab and plant some ivy or other groundcover. Then I could set up a bench and pots or something like that.

How far away from the slab can I plant the tree without the slab affecting the root development?

Does any of this sound like it would work?

John

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Grey
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I would think, depending upon the tree- 3 feet to 4 feet away should be fine. :)

A nice groundcover I'm in love with right now is common old Periwinkle. You have to cut it back 2x during the growing season, but much less invasive than, say, English Ivy. :)

Acer
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I'm not quite sure what you mean by cutting a groundcover back 2x. Please elaborate.

Is the periwinkle evergreen? And can it be used as a climber?

John

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Grey
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Periwinkle is an evergreen, but it does not climb on its own. I guess you could stake it where you want it to go up.

I just meant it needs trimming 2x a year as it escapes its bounds and starts heading places you don't want it to go.

It also has nice pretty purple flowers in April :)

grandpasrose
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Welcome to the Forum Acer! You could put raised beds on the concrete slab, but could only plant shallow rooted plants in them. I'm afraid roses have very deep roots, and shrubs also go quite deep. The other concern that I would have about planting directly above the concrete slab is heat. The concrete can get much hotter than the surrounding soil, and can actually burn the roots of plants on top.
I wouldn't worry about putting a tree next to the slab, as it still has three other sides to gain it's nutrients and water from, and eventually, it's roots will be deep enough they will be under the concrete. I have become partial to a couple of different groundcovers lately. One is "Ajuga Reptans" otherwise known as "Bugleweed", under 6", herbaceous having a bronzy or burgandy green leaf, and a spiky purple/blue flower in early summer. The other is "Houstonia Caerulea" otherewise known as "Quaker's Ladies", under 6", herbaceous green tiny leaf, and light blue to white blooms in summer.
Hope this gives you some help! :wink:

Val

decam0
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Instead of fighting the slab, why not go with it and put some decorative paving on top and have it as a terrace area?

Mamanature
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My back yard is about total concrete. Decam0, What type of decorative paving are you suggesting? I live in the US in Virginia. Thanks for your help.

thanrose
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This thread is 12 years old and the posters may not be actively watching it.

Most home and garden shops will have the square pavers that are 12 or 18 inch square and about 2 inches thick. That could be the quickest solution. Some styles will cost more than others, and the substrate has to be even or the paver will crack. You would still have to brush sand into the crevices.

Standard red brick is great and durable, but costs a good deal more.

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rainbowgardener
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Image

That shows raised beds I built on top of a concrete slab. It was really just a plain grey slab. I had a guy with the right tool come in a cut the grooves into it to make it look like pavers and then I stained it terra cotta. It was quite a convincing imitation of pavers for way cheaper. The beds were 16" deep. I wouldn’t try to grow shrubs or trees in them, but all the veggies I put in them including tomatoes did just fine.



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