When you first start thinking about building raised beds, it’s only natural to want to do it right. You want to build the right-sized bed, with the right materials and in the right location. But what if that perfect location is covered in gravel?
Can you build a raised garden bed on gravel? You can build a raised garden bed on gravel. If the gravel has dirt underneath, this may actually help to improve the beds drainage. Be sure, however, to carefully consider the raised bed height when building over a gravel surface.
Let’s take a more in depth look at some of the things you should consider when constructing your raised garden beds on a gravel base.
Table of Contents
1. Knowing is Half the Battle
The first thing you should consider is what is under the gravel. Is it dirt? Is it concrete? If you weren’t the one who installed the gravel, it is worth it to dig out a test patch at least 6 – 10 inches and see what lies beneath.
Doing this will help you determine how drainage might work for your garden bed. Drainage is an essential part of any garden. What is actually under the gravel isn’t as important as knowing what that is.
If the soil under the gravel has poor drainage, building your raised bed on top of the gravel can create a perched water table. Basically, this means that your raised bed would act more like a pot and less like a raised bed.
That’s only bad if you don’t know it is going to happen. If you know that the gravel is covering soil that drains poorly, you can build your beds a little higher and be sure they are layered with drainage in mind.
If the soil still drains well, you can build your raised bed with confidence knowing that you don’t have to do any extra prep work to ensure your plants don’t get over-saturated.
2. Build Your Raised Garden Beds Higher
Rock is hard for roots to penetrate. You will want to be sure that your raised beds are built high enough to allow your plants to fully root without hitting the hard gravel surface.
This is especially important if you are planting root vegetables to harvest like carrots, onions, and potatoes. A 6 inch raised bed over gravel might be perfect for planting and harvesting microgreens but you’ll want to increase that height if you want to grow other crops.
The higher the better. In most cases, when building a raised bed on gravel you want to make sure your height is between 12-36″ to have maximum versatility.
3. To Line or Not to Line
A question that comes up often for those looking to build their first raised beds is whether or not to line them. One of the things you should always consider is surface.
The question of whether raised beds need to be lined depends on a number of factors. Since we know you have a gravel base if you were considering lining your raised beds only to serve as a weed blocker, you may not need to.
While liners still have their place, like helping with soil retention, a pre-existing gravel base may already be serving the purpose of controlling weeds and even ground-dwelling pests.
5 Non-Traditional Surfaces You Can Build Raised Garden Beds On
While building a raised garden bed on top of nice, nutrient dense natural topsoil is absolutely the best option, it isn’t always feasible. Aside from gravel there are other unconventional surfaces that are OK to build raised garden beds on.
When you are building your beds on a non-traditional surface, just remember that each has its own set of obstacles that must be overcome. As long as you think about what you need to keep in and what you need to keep out, it’s easy to start formulating a plan for what will work in your situation.
Some other surfaces you can absolutely make work for your raised gardens include:
Concrete
You can build a raised garden bed on concrete. Bed height and drainage are going to be two very important factors to consider in the design. You will want to make sure your soil drains well and the bed is deep enough to accommodate the root structure for the type of plants you want to grow.
Asphalt
If you live in the city or the suburbs, don’t let that premium unused patch of asphalt deter you from living out your gardening dreams.
You can build a raised garden bed on asphalt. You will want to be sure to use a liner to prevent any chemicals from leeching into your soil. Bed height and drainage will be important things to plan for as well.
Grass
A sunny, grassy area makes a perfect location for a raised garden bed. Your soil has already nicely proven it can support growth. You can either use a tiller to loosen the soil or even just place the beds on top and build up the soil however deep you like.
Bricks
Raised beds can be built on top of a brick base. Typically it is best to go ahead and remove bricks from the area you are building the bed, exposing the soil underneath. If that is not possible, you can go ahead and build the raised bed right on top of the bricks.
If you do wind up building your raised bed on top of bricks, drainage and depth will be crucial to ensuring your plants are able to grow nicely.
You’ll want to use a liner to help keep the soil contained and serve as a barrier between the bricks but, otherwise, this solution can work if you aren’t able to expose the soil.
Pavers
Some yards, particularly those in urban areas, have been covered in pavers. Keep in mind that while it is always best to build raised beds over soil if possible, you can still build them over hard non-porus surfaces like pavers.
If you are building your raised garden bed over pavers you will want to be sure to lay down a liner on top of the pavers. This will help to eliminate any concerns of chemicals or byproducts leeching up through the pavers into the soil. Drainage and bed height should also be taken into consideration.