Is it a good idea to put a raised bed on concrete? In short, yes… if you do it properly.
While most people opt to place their raised beds directly on the soil, more and more people are opting for paved back yards. This is especially true in rental properties, as it’s easier to maintain and doesn’t develop weeds or require regular landscaping visits.
Just because your yard has lots of concrete doesn’t mean you can’t garden in it. However, it’s trickier to get started. Concrete can become stained by soil, so renters must take additional steps to get their beds set up. Drainage can become an issue as well, so it’s essential to plan that in advance too.
The benefits also can outweigh the drawbacks. You won’t have weeds surrounding your raised garden beds if they’re on concrete. Concrete also can help the soil to warm up more quickly in the spring, a real benefit if you want to start growing food early in the year. Let’s discuss everything you might face in getting your raised garden beds set up in the concrete jungle of your yard!
Raised Bed Planning and Preparation
There are a few things you need to take into consideration before you can begin. These basic principles apply to all gardens, but especially to those that will be placed on a concrete pad.
Location Is Key
All garden beds need access to sunlight, although depending on what you’re planning on putting in the bed, you may need less or more sunlight. Begin by watching your yard initially to see what areas are full-sun portions of the yard, which are part-sun, and which are mostly shaded. Depending on what you find, you can now plan out the initial locations of your beds.
The bottom of the bed needs to be on a flat surface. This is fairly easy if it’s on concrete, but if there’s a slope to your yard, that will be the direction where all runoff from the bed will flow to. Know in advance if it’s likely to pool up excess moisture somewhere on the hard surface. A reliable way to test this would be to turn a hose barely on to a trickle in the location you’re considering, then watch where the water goes.
When you build raised beds on top of pavers, you may have gaps between the individual pavers. Make sure to fill these gaps with sand or some other sort of material, just to guarantee your bed soil doesn’t get caught in between. Finer soil qualities can create the perfect habitat between pavers for weed development, so making sure you fill them with something less-appealing for roots is a good choice.
Plan also for good spacing between your raised beds when building them. You’ll need to get your garden cart or wheelbarrow between these large soil containers. The best option is to determine the width of anything that will need to move between beds and add about 6-8 inches of extra space beyond that. That way, when you’re using your cart, a tight turn won’t get you stuck between beds.
Watering System Woes
Unlike in other raised bed systems, installing a watering system through concrete generally isn’t an option. If you are considering a custom-built patio slab, you can lay out your watering system in advance and then pave over it. However, the rest of us have to opt for a different way.
Running a simple PVC system between the beds is an option, but it can be a trip hazard unless you keep it out of regular walkways. There’s also the option of running hoses to beds on concrete, but this can also be a trip hazard unless you plan wisely. If possible, place your watering hoses or pipes in the least-trafficked area of your garden.
There is always the option of hand-watering, and that’s just as easy as a built-in system. However, if you’d like to run your system on a timer while you’re on vacation, constructing a PVC pipe system to carry water to a drip system is your best bet.
Consider The Size You’ll Need
In an in-ground bed, growing plants have plenty of space for root expansion. The same is not true of any old raised bed on your patio. I always recommend choosing a taller raised garden bed than you’d expect to use. Something like the tall 6-in-1 steel garden beds in the Epic Gardening store will work beautifully to grow food, even on a hard surface, simply because you’ll have plenty of soil depth and the roots won’t encounter a hard slab at the bottom. You may opt to build a tall wood bed as well.
Installing Your Raised Garden Bed
Now that you’ve done the advance planning for your raised beds, it’s time to get them set up. However, garden soil can stain hard surfaces like asphalt or concrete. Thankfully, you can use a few simple tools to reduce patio staining caused by your large containers.
Begin by placing the frame of your raised bed in place on the patio surface. If it’s a steel frame, it’s a good idea to place a geotextile or landscape fabric inside the bed to prevent soil leakage and staining of the paved surface. For wood frames, you can staple hardware fabric inside to act as a mesh “floor” and then set the geotextile fabric in place inside of that. Either way, the landscaping fabric should go at least halfway up the inside of the bed.
Carefully fill in soil inside of the geotextile fabric using your raised bed soil blend of choice. Once you reach the top of the fabric, carefully cover it over as well, as the weight of the existing soil should keep more from going down the sides. Continue to add soil until you reach the top of the raised bed or the height at which you’d like the soil level to stop. It can take more soil to fill a tall raised bed.
If at any point in the future you have to dig down to the bottom of your bed, be careful to ensure that you don’t puncture the fabric. If you do accidentally create a few holes, your patio can start to become stained or discolored. In most cases, a quality pressure washer can clean the stain off, but you may also experience some soil leaking during drainage and settling. You can top off the bed with new soil, but it’s harder to patch holes.
Maintaining Your Raised Beds
For people who’re planting in the 6-in-1 raised garden beds, maintenance is easy. The galvanized steel won’t rust, so all you would have to do is to top off with compost or soil and plant it out.
A wood raised bed should last for quite a few years if you’re building your own. Over time, the wood will gradually start to show its age, and you may have to replace a board here or there if any rot starts to form. Keep a watchful eye on the bed to see if any rot develops. Even if it does, there’s a little time before you have to swap out the wood, so it won’t be an urgent issue.
You should have success growing plants in your raised beds as long as the soil drainage is right and you’re regularly weeding and maintaining them. Add a few inches of compost or compost blended with soil at least once a year, and you should experience excellent plant growth!