How to Trench Compost in a Raised Garden Bed

Learn how to turn your fall display full of straw bales and pumpkins into trench compost to refresh and maintain your raised garden bed!

What do you do with fall decorations when the season is over? The pumpkins, the hay, the straw bales, the corn stalks… I can’t bear to throw it away. The mini pumpkins often get turned into these cute DIY Pumpkin Centerpieces (beautiful gifts for teachers, neighbors, and loved ones), but I’ve found a very beneficial way to use the rest: Trench composting!

Raised garden beds are a great way to experience the joys of gardening while providing a bounty of vegetables or bouquets of cut flowers.  Compost will provide essential microbials and nutrients needed for healthy plants… Even better, it’s free and it helps keep organic materials out of the landfills.  

If, at the end of the growing season, you notice that your bed is woefully short of soil, you could take the fall and winter to refill your bed with compost provided from one source: your fall decorations.  The mums, gourdes, squash, corn stalks, bales of straw, and–last but not least–the scarecrow used to build the display.  

You might think that there is no way that you can sit an entire fall display into your raised bed.  However, the nitrate rich gourds, squash, and pumpkin can handle 30 times their weight in carbons, straw and corn stalks. This means you can chop it all up, bury it in the raised bed, and let nature do its job.

We are going to utilize the trench composting method to refill our bed to an adequate depth of composted materials for our summer garden.

What is trench composting?

Trench compost is probably the easiest way to create compost. Instead of having to turn and mix your compost several times a week, you layer it all once, then let it sit and have nature do its thing. This is such an easy way to enrich your soil and refill your garden beds without spending a fortune.

Right in your garden or raised bed, you dig a trench down the center of your planting area then bury your composting goods. We layer browns and greens, insulate it as much as we can (as heat speeds up the breaking down process), add some water, and wait!

How trench composting can refill and maintain your raised garden bed:

When I built my raised beds two years ago, I spent a small fortune to fill them up. To save money, I did add non-organic material at the bottom, then I added my own compost and rich soil to fill it up completely. Now two years later, I realized I had lost 10″ of soil through the natural planting, growing, and breaking down process.

Instead of spending another small fortune, I realized I had a huge load of materials, perfect for trench composting. The gourds, pumpkins, hay and straw bales, and corn stalks used for our fall porch display were exactly what my raised bed needed to prepare for the summer.

Additionally, this helps blend some of the benefits of a raised bed with the benefits of straw bale gardening. Straw is a great water holder, and having it mixed in with your compost and soil will save you money and time during the growing season.

When is the best time to start trench compost?

You can start trench composting at any time, but many people like to do it at the end of their growing season so that the soil benefits before next year. This makes a fall display perfect for trench gardening–Use the decorations on your porch until after Halloween or Thanksgiving, then spare yourself the waste by turning that same display into easy trench compost.

Can I compost food scraps directly in my garden?

There are many foods that are fantastic for your garden! Gourds, pumpkins, and squash are rich in nitrates, so they are perfect for pairing with a lot of carbon. Your compost needs both carbon (or “browns” like straw, hay, cardboard, wood ashes, corn stalks, leaves, etc.) and nitrogen (or “greens” like food scraps, gourds, dying mums, coffee grounds, etc.).

How to Trench Compost in a Raised Garden Bed:

Trench composting is very simple and doesn’t require a ton of work! Instead of normal composting that requires maintenance, this method allows you to get all the work done in a day so that you can reap the benefits months from now.

1 – Dig your trench

First you will need to dig out a trench from end to end of the bed.  Place the soil from the bed into wheelbarrow. If you don’t have one, simply work up half the bed and use the opposite side to hold the dirt until you have filled the first trench.

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2 – Break up & layer your materials

Now break open on the straw bales and place a thick layer of straw in the bottom of the trench. Next, chop up the pumpkins, gourdes, and squash, then spread them over the straw you just placed in the trench.  To break mine up, I used a flat blade shovel and a bottom cut from a plastic 55-gallon drum (in its previous life it was filled with soy sauce, used at a local manufacture of a popular marinade). Add another layer of straw to the trench. 

If you’re working one half of the bed at a time, that side of the bed should be getting very full–If you are satisfied, its time to move over to the other side of the bed. Cover over the first trench with the dirt from the other side.  Repeat the process with the straw and cornstalks and pumpkins, nitrates, gourds, squash.

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3 – Insulate & water the bed

Once you have the materials buried and dirt spread evenly across the bed, add a thick layer of straw to insulate the chemistry taking place down in the trench during the colder winter months. Now would be a good time to water everything down and cover the bed with dark-colored plastic tarp. Covering the bed with a dark cover will help generate some extra heat, helping the materials break down to have the bed ready for planting in the early summer.  

Finally, take a minute to step back and look at all you have been able to accomplish. The fall decorations have been repurposed to revitalize your raised bed with plenty of organic materials that will help conserve water and grow healthy plants and vegetables. Win-win-win!

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How long does trench composting take?

It will take several months for these materials to break down, especially because trench composting doesn’t heat up as much as an aerated, hot compost pile. That’s why I like to add the dark colored tarp–This helps soak up every bit of sunlight you get to keep the pile as warm as possible to help break down the materials.

If you are pulling down your fall display right after Thanksgiving (near the end of November), you should be ready to plant in early summer (May or June). The later you bury your display, the later your bed will be ready.

What can you add to trench composting?

While I focused on using my fall decorations for my trench composting, there are tons of things you could use instead. What you really need to remember is that you need a balance of carbon (browns) and nitrogen (greens).

Can I trench compost…

Leaves?

Dead, fallen leaves are considered a carbon or “brown” and are great for composting! It is best to chop them up first (run over them with the lawn mower on the highest setting) so that they break down faster. Leaves are great brown material for trench compost.

Rice?

Rice is considered a balanced food scrap–Not enough nitrogen to be considered “green” but not enough carbon to be considered “brown.” You can compost cooked or uncooked rice, but it can have some downsides. If your compost pile isn’t very warm and it takes the rice a long time to break down, it will easily attract pests and rodents as well as breed bacteria. Because of this, I would put rice in my aerated hot compost pile; I wouldn’t put rice in a trench compost.

Meat?

Meat is considered a nitrogen or “green” in the pile. You can compost meat, but it definitely attracts pests and rodents and can breed bacteria. This is another option I would save for the hot compost pile to prevent pests from disturbing the bed and spreading bacteria; I would not put meat in my garden bed trench compost.

Grass clippings?

Grass clippings are considered a nitrogen or “green” and are perfect for composting, including trench composting. However, if you are trying to compost clippings from a non-residential business, there is a chance that the herbicides used will cause the grass to take several months to break down. Residential herbicides don’t have this issue and break down quickly. Fresh grass does want to stick together which slows down the composting process, so it’s best to separate the grass as much as possible, layering it with other materials if you can.

Weeds?

Weeds can be composted and are considered a nitrogen or “green.” However, if temperatures are not high enough in the compost, the weeds could potentially sprout up into your garden bed later! For this reason, I would save the weeds for the hot compost pile where the temperature will be able to kill the weeds; I would not trench compost weeds.

Cardboard?

Layered cardboard will take quite a while to break down (I even use it as a weed barrier at the bottom of the raised garden bed). However, torn corrugated cardboard breaks down easily and is considered a carbon or “brown.” Tear the cardboard into small pieces and layer it as you would other brown materials in your trench compost.

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More Garden Tips:

• DIY Raised Garden Bed
• How to Create a No-Dig Flower Bed
• Preparing a Better Flower Bed with Spring Bulbs
• How & When to Plant Summer Bulbs
• How to Germinate Seeds that Require Direct Light