Is it a good idea to put a raised bed on top of concrete? In short, yes … if you get it right.
While most people choose to put their raised beds right on the ground, more and more people are choosing paved backyards. This is especially true for rental properties as it is easier to maintain and does not develop weeds or require regular landscape visits.
Just because your garden has a lot of concrete doesn't mean you can't garden. However, it's harder to get started. Concrete can be stained by soil, so renters will need to take additional steps to set up their beds. Drainage can also become an issue, so it is important to plan for this in advance as well.
The benefits can outweigh the disadvantages as well. You won't have weeds around your raised beds when they're on concrete. Concrete can also help the soil heat up faster in spring. This is a real perk if you want to start growing food earlier in the year. Let's discuss everything you can expect when setting up your raised beds in the concrete jungle of your yard!
Planning and preparation of raised beds
It is quite possible to put a raised bed on top of concrete. Source: Wikimedia Commons
There are a few things that you need to consider before you can start. These basic principles apply to all gardens, but especially to those laid on a concrete slab.
The location is the key
All garden beds require access to sunlight. Depending on what you want to put in the bed, you may need less or more sunlight. First, observe your garden to see which areas are full sun parts of the garden, which are partly sunny and which are mostly in the shade. Now, depending on what you find, you can plan the initial locations of your beds.
The bottom of the bed must be on a level surface. This is pretty easy when it's on concrete, but if there's a slope to your yard this is the direction all drains from the bed will flow. Find out in advance whether there is any excess moisture build-up anywhere on the hard surface. A reliable way to test this is to barely twist a hose on a trickle in the spot you are considering, and then watch where the water goes.
If you build raised beds on paving stones, there may be gaps between the individual paving stones. Make sure to fill in these gaps with sand or some other material to make sure your bed floor doesn't get caught in between. Finer soil qualities can create the perfect habitat between pavers for weed development. Hence, filling them in with something less attractive to roots is a good choice.
Also plan a good space between your raised beds when building. You'll need to put your garden cart or wheelbarrow between these large floor bins. The best option is to determine the width of anything that needs to move between the beds and add about 6 to 8 inches of extra space on top of that. This way, if you take a tight turn, you won't get caught between the beds when using your cart.
Irrigation system hurts
Unlike other loft bed systems, installing an irrigation system through concrete is generally not an option. If you are considering a custom-made patio slab, you can lay out your irrigation system in advance and then pave over it. The rest of us, however, have to choose another path.
Operating a simple PVC system between beds is an option, but it can be a tripping hazard unless you keep it off normal walkways. There is also the option of laying hoses for beds on concrete. However, this can also present a trip hazard if you don't plan wisely. If possible, place your irrigation hoses or pipes in the least crowded area of your garden.
There is always the option of hand-pouring, and it's just as easy as with a built-in system. However, if you want to run your system on a timer while on vacation, building a PVC pipe system to transport water to a drip system is your best bet.
Think about what size you need
In a ground bed, growing plants have plenty of room for root expansion. The same does not apply to an old raised bed on your patio. I always recommend choosing a higher raised bed than you would expect. Something like the tall 6-in-1 steel garden beds in the Epic Gardening store are great for growing food, even on a hard surface, simply because you have plenty of soil depth and the roots don't hit a hard slab below . You can also build a high wooden bed.
Installation of your raised garden bed
If you are building on paving stones, be sure to fill in the gaps, otherwise weeds can grow. Source: symphonyoflove
After you've completed the advance planning for your raised beds, it's time to set them up. However, garden soil can stain hard surfaces such as asphalt or concrete. Fortunately, a few simple tools can help reduce the stains on the patio caused by your large containers.
First, place the frame of your raised bed on the terrace surface. If it is a steel frame, it is best to put geotextile or landscaping fabric in the bed to prevent soil leakage and stains on the paved surface. For wooden frames, you can pin the hardware fabric inside to act as a mesh floor and then attach the geotextile fabric inside. In any case, the landscape fabric should reach at least halfway up the inside of the bed.
Carefully fill the soil within the geotextile fabric with a raised bed soil mix of your choice. When you get to the top of the fabric, carefully cover it too, as the weight of the existing floor should be more to keep it from falling down the sides. Add more soil until you reach the top of the raised bed or where you want the soil to stop. It may take more soil to fill a tall raised bed.
If you have to dig all the way to the bottom of your bed at a later date, be careful not to pierce the fabric. If you accidentally drill a few holes, your patio can become stained or discolored. In most cases, a good quality pressure washer can remove the stain. However, dirt can also leak out during drainage and settling. You can refill the bed with new soil, but it will be harder to mend holes.
Care of your raised beds
If your plant roots are shallow, a shorter bed is fine. Source: Ed Bierman
For people who plant in the 6-in-1 raised beds, maintenance is easy. The galvanized steel does not rust. So all you have to do is top up with compost or soil and plant it out.
A wooden raised bed should last a few years if you are building your own. Over time, the wood will gradually show its age and you may need to replace a board here or there if rot forms. Keep an eye on the bed to see if rot is developing. Even if it does, it will take some time before you need to replace the wood, so this is not an urgent problem.
You should be successful in growing plants in your raised beds as long as the soil drainage is good and you weed and care for them regularly. Add a few inches of compost or soil mixed in with compost at least once a year and you should see excellent plant growth!
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