If you’re ready to set up your raised vegetable garden, then you’re likely wondering about the bed’s location. And, you may be asking yourself can a raised bed sit on top of grass?
A raised garden bed can sit on top of grass. However, before you do so there are a few things to further consider. Namely, whether you should kill the grass beneath the bed and what are your options if want to remove the bed at a later date.
Read on to learn how to tackle both of these concerns.
Sitting Your Raised Bed on Top of Grass
Building a raised vegetable garden over your lawn is a great way to get started with gardening. However, one thing you don’t want is for any grass or weeds beneath the bed to start showing up in your vegetable garden.
Do I Need to Kill the Grass under My Raised Garden Bed?
How you’ll go about preventing weeds from poking through will depend on the depth of your raised bed.
It takes anywhere from 2 – 4 inches of coverage to smother most lawn grasses and weeds such as dandelions. Wiry or invasive grasses need greater depth of coverage, at least 7 – 8 inches.
When you smother grass, you prevent it from growing and it eventually dies.
If your garden bed will be more than 12 inches in height, the soil in the garden bed should be enough to suffocate any grasses or weeds. Taking extra steps here is not a necessity, but you may want to as an added precaution.
If your garden bed will be less than 10 inches in height, then you’ll definitely want to take additional measures to prevent the underlying grass from growing through the bed.
Your two main options are,
- Remove the sod before setting up your bed.
- Line the bottom of the raised garden bed to help with smothering the grass.
Now, you may be tempted to use weed and grass killer. However, I would caution against this.
First, weed killer takes time and often several applications. This means your gardening endeavor will be on hold until the grass is dead. Second, weed killer uses chemicals that can leach into the ground. Personally, I’m not keen on growing vegetables over top a chemically treated area.
Removing Grass Beneath a Raised Garden Bed
One sure way to take care of the grass beneath a raised vegetable garden is to physically remove the sod. And if your raised bed is going to be less than 6 inches in height, this should be your top choice.
To remove the sod, your need to first stake out the location of your garden bed. Then you’ll take an edger or shovel to start cutting away at the ground and lifting up the sod. Make sure the grass is neither too wet nor too soggy.
Unfortunately, digging up sod is time-consuming and physically demanding. There’s no getting around that. I know, because I’ve dug up my share of garden plots.
If you want to remove the sod but don’t fancy that much work, you can buy or rent sod removal equipment. You’ll have to determine whether your situation justifies the cost.
Smothering Grass beneath a Raised Garden Bed
Luckily, physically removing the sod is not your only option when it comes to dealing with the grass beneath your raised garden bed.
Instead of removing it, you can smother it.
Spring is the best time to take on this project before new grass has a chance to gain a foothold. Mow the area short first and make sure you leave the grass clippings where they fall. This leftover grass will compost and help feed the soil.
If you have concerns about grubs, treat the area with beneficial nematodes beforehand.
You’ll sometimes see gardeners at this stage using plastic to kill the grass. However, I don’t recommend this.
Plastic will smother the grass, but because heat trapped under the plastic increases the temperature of the soil, it can also kill the beneficial microorganisms in your soil. Something you don’t want to happen.
Once the raised bed is set in place, fill it in with a mixture of rich, loamy garden soil, compost, and or mulch. As I said, if you’re raised bed is greater than 12 inches, this may be all you need to do to take care of the grass below.
Should I Line the Bottom of My Raised Garden Bed?
On the other hand, if your garden bed is less than 10 inches in height, you’ll benefit from lining the bottom of your vegetable bed.
Don’t feel restricted if your bed is greater than 10 inches. Lining the bottom of your raised bed, regardless of the height, will help prevent grasses and weeds from breaking through.
When it comes to picking lining material, I strongly recommend using a liner that will decompose over time.
Cardboard and newspaper are two popular liner materials. But before you lay either down, there are a couple of things to keep in mind.
Cardboard: Cardboard is thicker than paper, and will take longer to decompose. Make sure the cardboard you choose is plain cardboard with minimal printing on it. Avoid any with a waxy coating or glossy print. Also, remove any tape or sticky labels before laying it down. And it’s a good idea to moisten your cardboard before filling in the bed with dirt.
Newspaper: Newspaper will decompose quicker than cardboard. Stick to black and white print and avoid newspaper with colored ink. You don’t want those colorants leaching into the ground beneath your vegetables.
With both newspaper and cardboard, make sure the pieces are overlapping. This prevents grasses from creeping up between the seams.
Weed Barrier: Using a fabric weed barrier is another option to consider. However, there are some limitations with this material.
First, it’s not as environmentally friendly. Second, the barrier can prevent your plant’s roots from reaching into the soil beneath the garden bed. If you have a shallow bed or are planting perennials, this can be an issue. Too, if you fill your bed with mulch or other composting materials, those materials won’t be able to breach the barrier to benefit the soil beneath.
If you like the idea of a weed barrier, consider using one specific to vegetable beds. This type of barrier is biodegradable and will break down more quickly into matter that will feed the soil.
Tip: Regardless of your lining choice, be careful with invasive grasses or weeds that like dark, moist environments, such as creeping Charlie. If these grasses are not smothered completely, you may unintentionally encourage growth.
For some more lining material options, take a look at the article from Davids Giant Vegetables.
What If I Want to Remove My Raised Garden Bed?
When preparing your raised vegetable bed, your aim is to kill the grass beneath. So, if you decide it’s time to remove the bed, and if you’ve done your job right, there won’t be grass down there.
But don’t worry. It’ll be a little work, but you can remove your raised garden bed and repair the ground below.
Start with removing any plants from the bed. As long as there aren’t any issues with diseases or pests, these plants can be composted.
Next, you’ll remove the soil from the bed. Now, depending on the size of the bed, you might have a bit of soil to deal with. But you have several options to deal with this leftover soil.
First, set aside some of the soil to layer on the ground beneath the bed. You can then use the remaining soil to bulk up other garden beds or fill in any patchy spots on your lawn.
If you’d like to learn more about reusing soil, check out my article on the subject
If want to keep the soil but aren’t sure where you’ll use it, then take the old raised bed and set it up elsewhere in your yard. This can then be used as a container for the remaining unused soil.
Lastly, if you’re not interested in using or storing the soil, then give it away to neighbors or post it as available on your social media sites. Gardeners are always looking to secure free soil.
Once you’ve removed the bed and your soil, you’ll be left with a bare patch of ground. Start by working some of the removed soil back into the ground to create a layer of that rich garden soil atop that bare patch. Smooth out the soil with a garden rake.
Next, seed and fertilize the bare patch. Make sure to keep the area damp until the new grass seed has taken hold. Over time, your lawn will grow to fill in the spot where your raised garden bed sat.
Final Thoughts
- A raised garden bed can sit on top of grass.
- Depending on the depth of your raised bed, you may need to take extra measures to deal with the grass beneath the bed.
- Those measures include physically removing the sod or smothering the grass.
- Lining the bottom of your raised garden bed will help with preventing grass and weeds from sneaking back up.
- Your lawn can be restored if you are done with your raised garden bed.
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