Plants and concrete

Does anyone here have any experience with soil placed directly on concrete, and its relative effects on plants growing in it? My concern is that the soil might leach something out of the concrete that would be somehow harmful to the plants (and ultimately the humans consuming the produce of the plants). This is entirely theoretical on my part, only supported by observing that the ground cover I planted in my front yard doesn't interact well with the concrete retaining wall, a correlation/causality pairing that may be fallacious (if I can dig into my bag of fifty cent words for description).

J.D. Ray wrote:Does anyone here have any experience with soil placed directly on concrete, and its relative effects on plants growing in it? My concern is that the soil might leach something out of the concrete that would be somehow harmful to the plants (and ultimately the humans consuming the produce of the plants). This is entirely theoretical on my part, only supported by observing that the ground cover I planted in my front yard doesn't interact well with the concrete retaining wall, a correlation/causality pairing that may be fallacious (if I can dig into my bag of fifty cent words for description).

This question is likely to be missed here, since it is tottally unrelated to the thread it is in, or even the forum. Much more likely to get responses if it were its own topic in the Plants subforum of Growies. The major impact of concrete on soil is to make it more alkaline.

Peter Ellis wrote:This question is likely to be missed here, since it is tottally unrelated to the thread it is in, or even the forum. Much more likely to get responses if it were its own topic in the Plants subforum of Growies. The major impact of concrete on soil is to make it more alkaline.

I waved my magic wand at it for you...

I have experience with grow beds on concrete if it helps any. I live in south Florida where soil pH is 8.5 - so I grow all of my vegies in raised wicking beds (concrete blocks stacked 3 levels high) on my back patio made of concrete. The first level is a plastic sheet with granite gravel filled one block high. It has a perforated 4 inch plastic flexible drain pipe that esses through it 3 times the length. On top of that first level is a plastic ground cloth. On top of that 2 blocks high is composted soil. Rain water from the roof can fill the wicking bed via the perforated pipe. I have had great results with this system. Zero complaints.

I have very limited experience growing on concrete but I do have a small section of garden atop a 10' x 10' concrete pad. Soil depth varies from 6" to 8". The location gets morning sun with dappled shade the rest of the day. This little area requires a lot more attention than my other garden areas because drainage is compromised, soil is not deep, and it dries out quicker when it's windy. But I have been successful using the spot to produce sweet potato cuttings, taro starts, germinate seeds for transplanting elsewhere (beans, tomatoes, broccoli & cabbage, kale). The lack of enough sun makes crop growing a challenge although New Zealand spinach likes the location.

I haven't noticed the plants being adversely affected by the concrete directly, other than moisture issues. If it were in full sun, then I'd be concerned about the soil getting too warm.

Perhaps your ground cover did poorly near the concrete wall because the soil became too warm, too alkaline, or too dry due to the proximity of the exposed concrete. Just a thought.

Thanks, those were both helpful responses. I will allay my fears.

JD

I'm not growing ON concrete but I do use concrete rip rap in various ways in my orchard. Keeping mulch on is one of them. I'm not too worried myself.