Do you desperately want to put down some soil and grow grass or plants, but all the space available has a concrete foundation? We have all been in the position of wanting to bring some greenery into our lives, but other things always seem to get in the way. But is this an unconquerable obstacle, or can you put soil on top of concrete?

You can put soil on top of concrete for a minimum depth of 4 to 6 inches to grow grass. You need to put 6 to 12 inches of soil to grow deep rooted plants such as vegetable and flowering plants. You need to consider drainage, leaching, and maintenance when adding soil on top of concrete.

Simply put, you can put soil on top of concrete. The process is fairly simple and ultimately similar to prepping and planting soil and plants in other conditions. However, working with the combination of concrete and soil together brings its challenges, which begs the question of whether putting soil on concrete is a good idea or not.

Can you put soil on top of concrete?

It is possible to put soil on top of concrete and even grow grass or possibly some other plants. While it is not ideal for the integrity of the soil, or the plants being grown, it is an option if there are no alternatives to bringing some simple greenery into a concrete area.

You can put soil on top of concrete, but it’s not the ideal scenario. I would recommend placing around 4-5 inches of high-quality topsoil over your concrete because it will compress over time and you want to make sure you have enough for roots to grow. – Jeremy Yamaguchi, CEO, Lawn Love

What are the problems caused by concrete under soil?

Considering the solid, impervious, and material factors of concrete, it shouldn’t come as much of a surprise to find out that putting soil on top of concrete can cause many issues. Putting soil on concrete may be possible, but is it worth it?

Soil on top of concrete will cause the following problems:

  • Drainage: Concrete is impervious to water, meaning that the water has nowhere to drain out of the soil; thus, the water levels will build, eventually causing the soil to become waterlogged.
  • Oxygen Levels: Waterlogged soil results in less oxygen being able to circulate. If grass–or any plant–can’t get the oxygen levels it requires, it will not survive.
  • Alkalization of the Soil: Cement is an ingredient of concrete that can pollute soil by changing its chemical composition.
  • pH and Plants: Leaching concrete will alter the soil’s pH levels, and plants are often sensitive to the pH concentrations they need to survive; thus, their overall health is threatened.
  • Heat: Concrete stores heat and faces the problem of getting too hot during the summer months. It would heat the soil and plants on and around the concrete and cause severe damage.
  • Maintenance: The combination of waterlogged soil, unhealthy plant’s growth, and more is enough to make the maintenance of soil on concrete a headache. From trouble with mowing the grass to the smell of stagnant water and unhealthy or dying plants, a lot of maintenance isn’t just necessary but also difficult.

You can take steps to try preventing as many of these problems as possible; however, it does not guarantee long-term success.

Concrete doesn’t drain and allow water to permeate and move through the soil shelf the same way that soil alone does. This can cause drainage issues and can cause your soil to hold more water. Crushed or busted concrete will drain better, so it may be a good idea to bust the concrete up or to use soil to cover up crushed concrete (after construction for example). The deeper the soil is on top of the concrete, the better. – Shelby DeVore, Founder, Farminence

Does concrete leach chemicals into soil?

Concrete can leach chemicals that are used in its manufacturing process into the soil. This chemical leaching is most likely to occur when soil is put on recently poured concrete. Some chemicals found in concrete include calcium oxide (lime), silicon dioxide (silica), aluminum oxide (alumina), iron oxide, and sulfate.

The slightly acidic nature of rainwater can promote the leaching of concrete into the soil. This can either occur when the rainwater travels down to where the concrete and soil meet or if the rain runs down from pavement and structures into the soil.

Once the concrete leaches into the soil, it changes its pH and chemical composition, making it unable to grow healthy plants.

How to put soil on top of concrete?

Putting soil on top of the concrete is fairly simple and straight-forward:

  1. Clean the Concrete: To begin, you must clean the concrete surface. Substances on the concrete can leach into the soil and have various harmful effects on it and any plants.
  2. Add the Topsoil: Lay down the topsoil on the area at the recommended or necessary height for what you are trying to achieve. It is recommended you make a raised bed to help avoid common problems of soil on concrete.
  3. Planting Seeds: Choosing and planting seeds is always an important step. If you are only looking to grow grass, then it is recommended that you choose a turf grass species, as their roots stay shallow.
  4. Maintenance: Once everything is done, it is up to you to maintain your grass or other plants and keep a careful eye on the topsoil for any issues it might face.

It isn’t ideal but you can put soil on top of concrete. If you are going to do this you would have to consider what you intend on growing. Most plants need 6 to 12 inches of soil to grow healthy roots. once there is enough space for the roots to grow it shouldn’t be a problem. – Nikita Legall, Gardener, Ah Grow!

How deep does soil need to be over concrete?

Soil needs to be at least 4 to 6 inches deep over concrete when growing plants. You need at least 4 inches when growing grass. But need a lot more when growing other plants with bigger root systems. 

If you intend to grow plants, shrubs, vegetables, or herbs on the soiled concrete area, the soil’s depth will determine whether their growth will be successful.

If you plant to grow grass, you need soil depending on the variety. The minimum soil depth for grass over concrete should be 4 to 6 inches.

Because of the concrete base, the root systems of these plants will meet a dead end at some point, and whether their roots have had enough space to sustain life is going to depend on how much topsoil we have put down. Stunted growth in plants can cause various health problems.

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