What do I put on the bottom of my raised garden beds?

Raised garden beds are great for growing herbs and vegetables in your home garden.

But it is important to remember that raised garden beds are not guaranteed to yield good results. You must create an excellent growing environment inside your garden bed to be successful. 

And starting your raised garden bed the right way is critical. Our method will save you money and help create a fertile, well-draining garden bed with good aeration and a constant soil moisture level.

TL;DR: Create a weed-blocking layer by placing cardboard or garden fabric at the bottom. Next, on top of this layer, place branches, dry leaves, garden waste, even dry firewood, logs and thicker stems, and pretty much any other brown and dry organic material you have lying around. 

Read on to learn how we use and start every raised garden bed we have ever built.

Some of the raised garden beds we have build in our garden
Some of the raised garden beds we have built

The best way to fill the bottom third of your raised garden

It is helpful to think in thirds when building a raised garden bed. And here in this article, we will fill the bottom third of a raised garden bed.

Read the article “Guide to building a raised garden bed (DIY for less)” for a step-by-step guide to building a raised garden bed from scratch for information about the other two-thirds.
Dry firewood can be an excellent filler for the bottom third of your raised garden bed
Dry firewood can be an excellent and inexpensive filler

Every fall, we spend time preparing our garden for winter. Sorting everything before winter prepares us to plant garlic before the first frost and prepares our garden to grow leafy greens as early as January the following year.

Putting our garden to bed always creates a lot of waste. We prune and cut back bushes and trees like our sour cherry trees, remove twigs and branches, and rake all general areas to remove fallen leaves and pine needles.

Some of the garden "waste", branches and compost that will fill my new raised garden beds
A good clean-up gave me a lot of materials to use for my new raised garden beds

Instead of renting a trailer and driving to the local recycling center, we use this organic matter as food and nutrition for our vegetable gardens.

Logs and thick branches take time to break down and decompose into compost. We have plenty of time. Plants need 15-20 cm (6-8 inches) of quality soil to develop healthy root systems. There is no good reason to fill your whole garden bed with expensive quality soil. 

Why use logs and branches on the bottom third of the garden bed?

There are several advantages to using logs, thicker stems, branches, and other plant matter as a foundation for your raised garden bed.

  • Logs and thicker stems help retain moisture, making it easier to retain constant soil moisture on hot summer days.
  • Logs and branches create natural gaps in your bed, helping with soil structure, drainage, and aeration. 
  • You save money on renting a trailer or driving to the recycling center.
  • Spend less on quality soil; you only need to fill the top third with quality soil.
  • As the matter decomposes, it will create an excellent environment for worms and microorganisms, making the soil more fertile.
  • The feel-good factor is when your garden manages to create a circle of life pattern where garden waste is used and not discarded.
I recommend using borders or digging down below ground when you use logs, branches, etc., as a foundation for your raised garden bed. Building raised garden beds with sloped sides makes it harder to create a flat growing area.

3 types of raised garden beds

There are three main types of raised garden beds, and we use two of the three in our gardens.

Start all 3 garden beds with a bottom layer of branches, logs, and other brown organic materials.

1. Raised garden beds with borders

We like raised garden beds with borders as they are easier and less expensive to build.

There are several advantages to bordered garden beds.

The border creates a structure to hold the soil and can also be used to support stakes or plant covers as needed.

Another advantage is that the edge forms a level of protection against unwelcome animals and pests. 

Finally, the frame does help to retain moisture better than a completely unprotected raised garden bed.

The two main disadvantages of using borders are:

  • Creating a border involves spending money on materials.
  • Gardening is done at ground level, which is less comfortable than using a container-raised garden bed.
Getting help cutting borders for a raised garden bed
Getting help cutting borders for a raised garden bed

We have 4 raised garden beds with borders measuring 180 cm x 150 cm (70 inches by 60 inches). We primarily grow vegetables, leafy greens, and herbs in these garden beds.

2. Raised garden beds built like containers

Raised garden beds built like containers are pleasing to the eye and very easy to work with.

The firm container structure allows for easy covering with plastic, fabric, or glass panels if needed.

The container-raised bed helps retain soil moisture and requires less frequent watering than the other types of raised garden beds.

As the container sits on the ground, the containers are also “less work to move.” I am not saying they are easy to move, as they tend to be very heavy.

One of our closed-bottom square raised garden beds
A square closed-bottom raised garden bed container

One of the main advantages of raised garden beds is comfort. Build your raised garden bed to the desired height and enjoy gardening in a more relaxed and upright position.

The two main downsides are that raised beds are more expensive to build, and it does take time and effort to make them. 

We have 6 raised container garden beds, and they are all built from materials left over from other projects. 

  • Four deep closed-bottom square raised beds, measuring 82 cm x 82 cm (32 x 32 inches). Here, we grow impressive-looking vegetables like chilies and tomatoes.
  • Two rectangular-shaped open-bottom garden beds with an above-ground height of 40 cm (16 inches), measuring 160 cm by 90 cm (63 x 35 inches). Here, we grow herbs, lettuce, and other leafy garden vegetables, as well as most other non-root-type vegetables.

3. Raised garden beds with sloped sides

Garden beds with sloped sides are easy to build. They are also the least expensive of the three raised garden beds.

The main reasons we do not use garden beds with sloped sides are:

  • a smaller growing area as the sides are sloped
  • completely exposed to the elements and dry out quicker
  • harder to work with as the soil is not held in place

It is easy to construct a border, and you do not have to use expensive or store-bought materials. Use what you have – boundaries will make your gardening easier.

I find it easier to manage the soil quality when using a raised garden bed. As the space in each garden bed is smaller and defined I have found it helpful to attack one raised garden bed at a time. And working on a rolling schedule has helped me to over time have a better growing environment for our herbs and vegetables across all our garden beds.

Helpful sources:

University of Maryland, College of Agriculture and Natural Resources

Texas A&M AgriLife Extension (Priscilla Files, Michael Arnold, Douglas Welsh, and Frank Dainello)

Mattias Magnusson: Hello, I'm Mattias, a passionate and experienced gardening enthusiast. I am the creator of MattMagnusson.com, your guide to year-round herb and veggie growing. Let's simplify green living, no matter your space or location.