Is Filling Raised Garden Beds with Logs Ever a Good Idea?

I've seen gardeners fill their raised beds with all sorts of things to save money on soil. I'm all about saving money on soil and using fewer soil bags, but I've found that putting big chunks of wood at the bottom of your raised beds is not a good idea.

Listen, I've been designing and installing raised-bed kitchen gardens for almost a decade now. I've created over 500 kitchen gardens for my clients and taught thousands of students how to start their own. And I do not think that you should put logs at the bottom of your raised beds.

Let me explain why that is and then I'll give you the best alternative if you still want to fill your beds with something other than great soil.

Logs Have an Unpredictable Effect on Your Soil as They Decompose

I really only want one main process happening in my garden, and that's plant growth. What I don't want is for anything in the soil to be decomposing at the same time that my plants are trying to grow. Because that means I now have two things pulling nitrogen simultaneously from the soil medium—the plants and the fungi involved in breaking that wood down and turning it into soil.

This is similar to what happens when you put mulch on your raised beds. Mulch is, after all, just smaller pieces of wood.

This decomposition process is great for forests where trees have deep root systems and all the time in the world to grow. But we're mostly growing annual plants in our raised beds. I don't want any competition for my plants during their short life cycle in the garden.

What I don't like about having things breaking down in my garden is the unpredictability of it. Will it be a slow, continuous pull on the nitrogen from the surrounding soil? Will I need to amend my soil with nitrogen for a month or for years to come? There's not really any way of knowing.

To me, it's not worth the gamble that those logs could negatively impact my soil for a while. I can't get this season back if it doesn't go well, you know?

I Want My Beds to Be Filled With an Incredible Growing Medium from Top to Bottom

I know that raised beds are expensive, and then you have to pay for the soil to fill them on top of that. I'm not sure where the expression "dirt cheap" came from—it wasn't raised bed soil, I can tell you that! But one of the main reasons for having the raised beds in the first place is being able to start fresh with great soil.

Great soil is not only nutrient-dense and filled with air pockets, it's also finished. It's done decomposing. It can just sit there and provide an incredible growing medium for your plants, and your plants can rely on this soil day after day.

I like to compare this to raising kids. When children are going through major changes—let's say during puberty, for example—they need their home life to be stable so they can navigate everything else that's changing.

The same is true for your plants. Your plants have to weather all kinds of ups and downs: rain, heat, cold, wind, pests. Meanwhile, they're trying to produce leaves, flowers, fruit, and then seeds. The last thing I want to give them is more change. They need a steady environment with nutrients that are always available.

You're Still Going to Need to Fill Your Beds with Soil... Eventually

If you fill the bottom of your beds with stuff that isn't soil to save money when you're installing your garden, you're just delaying the purchase of soil. Sure, those logs and sticks will eventually become soil, but they're going to lose most of their mass. Within just a matter of months, your soil is going to start sinking.

I tested this out in one of my raised beds. I filled the bottom with logs and leaves and sticks, jumped on it to condense it, and then filled the rest of the bed up with soil. And it felt great to only need a few bags of soil. But within a couple months, the soil level had fallen to 6 inches below the top of my raised bed. In the matching raised bed that I filled completely with fresh soil, the level had only dropped about 1 inch.

So you may only have to buy a couple of bags of soil now, but you'll need to go buy more bags later to add to the top of your raised beds. You'll spend the money you saved today within the next year.

After installing hundreds of gardens for clients, I've consistently found it's best to just fill up the beds with soil in the first place. When I return to those gardens later, I only ever have to add an inch or two of compost to the top.

Then What Should I Fill My Raised Garden Beds with?

Now, I hear you saying, "But Nicole, I just don't want to buy all that soil right now." There are some other options you can do, but just know that you will still need to add more soil at a later date.

Instead of logs or sticks, you could fill the bottom of your raised bed with leaves or straw. These options will pull less nitrogen from the soil to break down. Plus, it's much easier to compact them. I recommend stomping on them for good measure and then watering them down before you add soil on top. Use as much soil as you can afford at the moment. In a season or two, it'll be time to top your beds off with more soil.

One thing I absolutely do not recommend is filling the bottom of your bed with plastic water bottles. We're exposed to enough microplastics as it is without adding more to our soil. Use only natural materials to fill your raised beds.

What About Hugëlkultur?

Hugëlkultur has its merits, but it works best outside of a raised bed. Instead of building an outer structure, you use logs as the base of your garden and lay natural materials on top of the log to create a mound that you can plant on top of. The key here is that the entire mound is open to the elements.

When you use this ancient technique, you're in it for the long haul. One of our goals when using raised beds is to get that immediate payback instead. I want great results the same season.

So I'm not coming against hugëlkultur by any means. I just don't think it has a place when you're trying to grow a ton of plants in a small space and in a quick amount of time.

Fill Your Raised Beds with Soil for the Best Results

At the end of the day, we want the main thing that's evolving to be our plants. We want to create a nice, nutrient-rich environment for our plants so that they can do their magical thing. And for that reason, I don't recommend using logs. The money that you could save by using logs is not worth the issues that might arise.