7 Cheap Ways To Fill a Raised Garden Bed

If you’re looking for inexpensive ways to fill your raised garden beds, you’ve come to the right place. Garden beds are invaluable in creating a controlled growth environment that allows your vegetables, herbs, and flowers to thrive. So, how can you fill up your raised beds without spending a fortune?

The cheapest ways to fill a raised garden bed include using recycled cardboard, homemade compost, sand, and bulk-bought topsoil. Plant debris such as logs, landscape fabric, and plastic are also incredibly useful in filling up your beds and enabling them to support the growth of your plants. 

We’ll now go through all the cheapest materials you can use to fill your raised garden beds. We’ll discuss how you can use each one and how to layer up your beds effectively. We’ll also discuss a few myths, what you shouldn’t be putting in your beds, and how much they should be filled for optimal results. 

1. Cardboard

Cardboard is by far the cheapest material to use in your garden beds. After all, who doesn’t have old cardboard boxes lying around? Maybe you’ve recently helped a friend move, or you like ordering goodies on Amazon – whatever the case, you can use those old boxes to help your plants thrive. 

Placing layers of moistened cardboard across the bottom of your beds is an excellent way to promote moisture control and retention, keeping the soil nice and moist for extended periods. This also enables you to water your raised beds less frequently, which is great for busy gardeners.

The reason you need to keep the cardboard damp at the beginning stages of raised bed construction is that pests such as termites adore dried cardboard if left out for too long. So give it a good spritz before placing it at the bottom.

The best cardboard to use is corrugated cardboard – this has little ridges across it that are made of several layers, allowing it to withstand the water. Additionally, you should try to steer clear of cardboard that has ink or print stamps on it – chemicals can seep out into your raised beds and affect the balancing properties of the soil. 

Over time, the cardboard at the bottom of the raised bed will break down and turn into mulch – which will provide ongoing nutrients that will seep into the soil and help the plant roots get everything they need to live a long and healthy life. 

2. Compost

Using compost in any gardening endeavor is pretty much a no-brainer. It’s an excellent and inexpensive way to promote nutrient-rich soil, and you don’t even need to buy anything to produce it. Instead, you can make it yourself using your scraps from the kitchen and a few other little household items.

Compost is essentially made out of raw green and brown materials, providing carbon and nitrogen supplements that will keep your plant roots (and the soil) happy. 

Here’s a breakdown of what constitutes green or brown materials for composting:

  • Green materials contain nitrogen. Nitrogen is essential for plant growth, so including these materials will boost your compost mixture tenfold. Green materials include used coffee grains, grass clippings, egg shells, and other leftovers from your kitchen, such as old vegetable ends. 
  • Brown materials contain carbon. Carbon is used by plant roots to “breathe” – meaning they transfer the carbon into sugars that can help them respire. This can help with photosynthesis and other vital components of plant growth. These materials include wood mulch, newspaper, and plant debris.  

The great thing about compost is that it allows you to use a large amount of your old kitchen waste instead of throwing it away. If you and your family often consume stuff like vegetables and eggs, you’ll have plenty of stock for your compost pile

You should have an equal amount of each of these components for the optimal results. Remember that the brown materials can help to provide better aeration for your compost, so if it’s looking too saturated, you can always add more to balance out the mixture. 

It’s probably best to keep your compost mixture outdoors since it can get a little smelly! You can use an old plastic bin to make it – just make sure that you don’t seal it too tightly since it needs to have access to air to break down properly. 

Disclaimer: While you can use kitchen waste for compost (and most of it is perfectly fine to use), you should never put dairy products or meats in the pile. These will decay over time, and you’ll find insects infesting your pile, and you’ll have to start all over again. 

Place your compost in layers throughout your raised beds, sprinkling it in between the other additives on this list. You don’t want to have too much (and you can’t grow your plants in compost alone), but a good handful over each layer should do the trick.

3. Sand

Sand is a cheap material that can give poorly-drained soil a good boost. I’m not talking about beach sand or play sand – I’m talking about coarse sand, which is most often used in construction. I’ve written an extensive guide about coarse sand for gardening. Don’t miss it: Coarse Sand for Gardening: 7 Things to Know

If your raised beds are particularly tall, coarse sand will definitely come in useful. Spreading the sand across the bottom of your raised beds will ensure good drainage so that your plant roots won’t be saturated every time you water them. 

If you’ve got clay-based soil, you’ll need to use quite a lot of sand since only using a little bit will end in a very heavy soil mixture. However, if you’re using store-bought topsoil, then sprinkling it over two or three layers at the bottom of the garden bed will suffice. 

Coarse sand is relatively inexpensive to purchase, and you may even be able to get some leftover sand from a local builder. It’s used all the time to make concrete and other materials, so they’ll likely have some lying around. 

If that’s not an option, you can buy smaller quantities at your garden store or online.

4. Topsoil

Using a good quality topsoil doesn’t have to be expensive. The trick to spending less when it comes to topsoil is to buy it in bulk. Commercial topsoils are typically strained so that they don’t contain any hard pebbles, sticks, or other materials that can hinder the growing process. 

Topsoil is typically considered the soil that sits on the top 15 inches or so of normal garden soil. Topsoils tend to be full of microorganisms and helpful nutrients that plants love, but the ones you buy in the store may not be quite the same since they’re strained to ensure they don’t contain diseases.

Therefore, using it in your raised garden bed, along with some good quality organic material (such as compost), is a must. You can figure out exactly how much you need if you know how many square feet your raised garden beds are – and then buy double in big bags so you can save money. 

5. Fill Your Raised Beds With Plant Debris

Plant debris can be anything from grass clippings, fallen leaves, or wooden logs you find in your garden. This is pretty much free since most gardens contain some form of plant debris, and you can easily reuse the materials rather than simply throwing them away. 

One of the options you have is called Hügelkultur. This is essentially a process of using old tree trunks, big branches, or logs to create a bed of nutrients for your plants. When the wood decays, it produces helpful nutrients and microbes that can boost the life of your soil and give your raised beds a new lease of life. 

To be honest, Hügelkultur is not wholly dissimilar to composting – but you’re not using multiple ingredients to start the process. The decaying wood simulates natural decomposition systems that allow your plants to remove the nutrients they need from the rotting materials, and your soil will become rich and arable in the process. 

The idea is to take pieces of these wooden materials and place them at the bottom of your raised garden bed. Cover them with soil, organic materials, and the other things on this list, and you’ve got yourself a plant playground raring to go. The wood eventually begins to feed all the microbes living in your garden beds, and you’ll have a long-lasting, simple solution for your beds that won’t cost you a penny. 

Another excellent component you can use from your garden is leaf debris. This could be leaves that have fallen from the tree in the Autumn months that you would typically just sweep up and throw away. However, they can be incredibly useful in your raised garden beds – and they are entirely free.

The best way to use leaf debris is to shred them up as small as possible so you can evenly distribute them throughout the raised beds. You can mix them right into the soil layers – ideally between two to three layers for the best results – and just leave them to rot, releasing their gorgeous nutrients for your roots to take full advantage of. 

Leaves are essentially organic materials, similar to compost. However, unlike compost, they don’t need time to develop and can be thrown straight into your raised garden beds. 

6. Landscape Fabric

Landscape fabric is probably the most expensive thing on this list since you won’t be able to find it lying around at home – but it’s worth the spend. You can find cheap landscape fabric, and if you only need it for small garden beds, it’ll be even more affordable. However, if you spend the money upfront and buy a good quality fabric, it will last you a long time, and there are no maintenance costs to worry about. 

Landscape fabric is helpful if you’re particularly concerned about weeds or other pests digging into your raised beds. It will stop the growth of weeds, and they won’t be able to penetrate the fabric. 

Good quality fabric can also be used to prevent your soil from becoming too saturated, boosting the drainage levels of your beds and keeping the soil fixed at the bottom without washing away any of those essential nutrients. When it rains heavily, the soil could get washed out of the base through cracks in the beds – but landscape fabric stands as a protective barrier, keeping your soil layers intact over time. 

You can use landscape fabric along the sides or the bottom of your raised beds. 

7. Plastic

Plastic works in a similar way to landscape fabric. You can use it as an effective liner for your raised beds if you’re worried about fungus or if you want to protect the integrity of your raised bed itself. Most raised beds are made from wood, which can deteriorate eventually, and a strong plastic lining can maintain its integrity while protecting your plants from extreme temperatures

If you use plastic along the edges of your raised garden beds in very cold weather, you’ll find that your soil won’t get too cold too quickly, effectively killing your plants. It’s usually best not to use plastic along the bottom of your raised beds since this could end with water pooling at the bottom of the beds and saturating the bottom few layers of the soil, drowning the roots of your plants.

Before you place all the layers of your raised bed, pack some plastic into the sides of the bed. Once you fill it up, the plastic will protect the wood and will keep the whole structure stable – even in extreme weather conditions. 

What Shouldn’t You Put in Your Raised Garden Beds?

All the soil additives listed above are excellent for promoting good growth in your raised garden beds, but there are a couple of myths that need to be addressed. 

For one, don’t listen to anyone who tells you to put rocks in the bottom of your raised beds. People used to think it would protect the integrity of the beds and keep the soil inside, but actually, it causes water to pool in the bottom of the structure and will thoroughly saturate the area. 

That said, small pebbles are fine (if you use them sparingly) since they are small enough that drainage is still possible and won’t result in a waterlogged structure. However, big rocks will stop aeration channels throughout the soil, and longer roots may die in the process. 

One of the biggest problems with using rocks in raised beds is that they attract insects such as termites and slugs. Depending on what you’re growing, this could completely destroy your raised bed, and you’ll have to use some kind of chemical fertilizer to resolve the issue. Pests love those dank areas where they can burrow and multiply, so rocks will inevitably make this problem worse. 

If you do decide to use pebbles or gravel at the bottom of your garden beds, don’t cover the whole area. Make sure that you leave plenty of gaps so that aeration can still happen and water can easily drain through the bottom, leaving your soil and compost layers perfectly intact. 

Do Raised Beds Need To Be Filled to the Top? 

So, you’ve got all of these gorgeous layers to fill up your raised beds, and you hardly have to spend a thing to do so. But do you need to be filling them all the way to the top?

Raised beds need to be filled to the top – or at least to around a finger’s length from the top of the structure. It may look like a lot, and you might be scared it will all tip over the side, but once you’ve watered the beds, all those materials will pack down.

Watering the layers of soil, compost, plant debris, and sand will cause all those individual layers to become heavier and eventually sink into one another. Remember that you should be watering the area before you plant anything since this will help the plants and their roots adhere better into the soil and settle themselves into the moist environment.

Once you’ve done this, leave the bed for a day or so. When you come back to it, you’ll likely see that the layers have sunk down – and you may even want to add in another couple of layers to really make the most of the space. 

In this situation, you really want to pay attention to what kind of plants you’re growing. If you’re growing shallow-rooted plants (such as onions), then you may not need too much depth in your raised beds. However, if you’re growing long-rooted plants, such as winter squash, you’ll definitely need a lot of space to work with. If you’re growing plants with roots that stretch wide and deep, then fill your beds right up to the top. 

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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