There are numerous considerations one should keep in mind when making a raised garden bed, including what material to use for the enclosing structure and what type of soil to use in the bed. One of these considerations is the ground under the garden bed. If you plan to place your raised garden bed over the soil, will you first need to till the existing soil?
You don’t need to till the soil under a raised garden bed in most situations. However, you may need to prepare the ground by pulling up weeds and clearing away rocks. In the process, you may end up digging into the soil, depending on the preparation method and the soil’s current condition.
In this article, we’ll look at how you should prepare the ground under your raised beds in further detail. We’ll also look at why tilling is generally not recommended in both commercial agriculture and home gardens.
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Preparing the Ground for a Raised Garden Bed
While you can build raised garden beds over most types of surfaces, including concrete and tabletops, there are certain additional steps you must take if you’re building your beds over the ground.
This is because if the ground is properly prepared, the roots of your plants will have additional space to grow, which is good for deep-rooting crops. They will also be able to access the nutrients in the ground instead of depending solely on soil additives.
You can prepare the ground for a raised garden bed in several ways. However, the two most common ground preparation methods are no-dig and low tilling.
Here’s a more in-depth review of each method.
The no-dig method is precisely what it sounds like – a method of preparing the ground that requires no digging or tilling. It is a low-effort method that is great for your back, but it requires that the soil be conducive to plant growth. If this is the case, the main issue you’ll likely face is grass and weed growth preventing you from building your raised bed.
Here’s how to prepare the area on which you will put your beds:
- Slash or mow down weeds and grass as much as possible.
- If the area has grass on it, cover it with organic manure and lime.
- Cover the area with organic light-blocking material. Generally, newspaper does the job very well. Make sure to overlap the newspaper so that no weeds or grass slip through the cracks.
- The newspaper (or other light-blocking material) will smother the grass and weeds. The material should be organic so that it will also break down over time. If you don’t have a newspaper, consider cardboard instead.
- Add a layer of compost to act as the growing medium. This should be very thick, about 4-6 inches (10.16-15.24 cm).
You can now start building your raised bed over the compost. By the time the roots are long enough to reach the ground, the light-blocking material will have decomposed, and the compost will have become a part of the soil on the ground (source).
The low tilling method involves digging into the soil and performing some tilling. This method is used when the soil is not very conducive to plant growth, such as when it is highly compacted or full of rocks and stones.
For this method, you should:
- Mow or slash down the grass and weeds.
- Dig out the grass and weeds completely.
- Dig up the top layer of the soil to get rid of grass and weed seeds that may affect your raised beds. This also makes it easier to see what stones and rocks are blocking the soil.
- Save the top layer.
- Remove the rocks and stones you find. If there is significant plant debris (such as large tree stumps), remove that as well.
- Loosen up the soil a little with your shovel. Don’t dig around too much – you’re not trying to till the soil thoroughly as you would in traditional gardening.
- Add composted organic matter to the soil. You can use manure, compost, or a mixture of the two.
- Place the top layer over the new organic layer and gently mix the two.
While this method does require a small amount of tilling, it is much less intensive on the ground than mechanical methods such as using a rototiller. And unlike traditional tilling methods, you will not have to repeat the process annually. As long as the soil avoids compaction, the initial low tilling will last for years (or a lifetime if you’re lucky) without needing to be repeated.
Why Tilling Is Bad
Most people giving advice about building raised garden beds and even traditional in-ground gardens will recommend against tilling unless there is no other option.
This is because, while tilling was long seen as the best way to prepare the ground for agriculture and gardening, a growing body of evidence shows that it is harmful to the soil and the environment.
Here are the specifics of why tilling isn’t recommended:
- Contrary to popular belief, tilling damages the soil structure and can actually increase the risk of soil compaction instead of aerating it (source).
- Damage to the soil structure also makes the soil looser and more susceptible to erosion (source). The problem is exacerbated if you live in an area with heavy rains and winds.
- In some cases, tilling can expose dormant weed seeds to ideal growth conditions, prompting more weed growth rather than destroying it.
- Tilling destroys organic matter in the soil, including microorganisms (source). While there is increased soil fertility in the short term, it is destroyed by the loss of microbes in the long term.
Tilling is also labor-intensive, even if you have a rototiller. It’s an inconvenient and often painful option for people with mobility and back problems. Unless there is no other option, it’s always best to avoid disturbing the soil.
That said, light tilling is required in some cases. For instance, when the soil is too compact and needs light aeration or when there are a lot of rocks blocking effective plant growth. Ultimately, whether you need to till comes down to the condition of the soil you’re working with.
You do not have to till the ground under your raised garden beds unless there is debris and rocks that would block the growth of your plant roots.
Tilling should be avoided in all types of gardening unless there is no suitable alternative, as there is significant evidence showing it increases soil erosion and negatively affects soil quality and fertility over the long term.
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