How to fill a raised garden with free materials

With food security being much on people's minds at the moment, many of you are wanting to start new gardens or expand your existing ones. I've certainly felt the urge to increase production here on our little urban homestead.

To that end, I thought it would be helpful to share how I filled all our raised garden beds almost entirely from free materials I gathered. Hopefully it will inspire some of you to give it a try.

Our yard before the raised gardens were built.

When we moved onto our property four years ago, there were a few trees dotted around, but no vegetable gardens or edible plants.

Ben building a garden bed to wrap around two sides of our deck. 

My amazing brother-in-law, Ben, swooped in and built us five raised garden beds and a wraparound garden bed for our deck, using reclaimed fencing from his brother's farm. That was a wonderful gift as buying our house had used up all our savings so I didn't have much to put into gardening, even though it was something I really wanted to do.

Three of the raised beds Ben built. 

Our lack of spare cash meant I had to get creative filling all these wonderful new gardens. This video by Janet Luke inspired me to look around for free resources in my garden and neighbourhood.

I drew the diagram above to show you the approach I took to filling my gardens. Now I'll talk you through the process.

Layer 1 - Brown
You can build your raised garden beds directly on grass/weeds, but you're going to want to do something to kill those existing plants. I layered flattened cardboard boxes, then several layers of newspaper and then fallen cabbage tree leaves inside my raised beds, directly over the grass to form a thick weed mat layer.

Tip 1: Use matte cardboard and newspaper, not glossy.

Tip 2: Overlap the cardboard and newspaper so there are no gaps for grass and weeds to grow through.

Tip 3: Wet everything down with a hose before you add the next layer, to hold it in place and help the fibres of the cardboard and newspaper to knit together and form an effective weed barrier.

Layer 2 - Green
Now it's time for a green/nitrogen layer to help the cardboard break down over time so that worms can crawl through and start percolating your garden. Make this layer about 10cm thick. You can use grass clippings, seaweed, animal manure, green hedge clippings, used coffee grounds, sheep dags or kitchen scraps - just whatever you have access to.

Layer 3 - Brown
Because there are going to be many more layers above this one, this is a good place to use up large sticks and small branches collected from around your garden.

Placing branches at the base of a garden is a method known as hugelkultur gardening. It's brilliant because it uses up all those scrappy sticks and branches that otherwise end up messing up your yard. Also, these branches will benefit your garden by retaining water, increasing fertility and producing heat as they break down, thus helping plants grow even during the colder winter months.

Wet the branches with a hose before you start adding your next layer.

Layer 4 - Green

Spreading used coffee grounds in my layered garden.

It's now time for another nitrogen layer. This needs to be extremely nitrogen-rich to help break down the branches and sticks of the hugelkultur layer, otherwise those branches can end up competing with your plants for nitrogen.

I'd be tempted to use animal manure, blood and bone or coffee grounds for this layer, if you have access to any of them. Otherwise, you could use grass clippings and then pee on them for an extra nitrogen dose. (I could be being overly cautious in suggesting the use of urine, but I think it's better to be safe than sorry. And hey, it's free!)

Spray this layer lightly with a hose before you start building your next layer.

Layer 5 - Brown

Carbon-rich layer of fallen leaves.

Now that we've finished with our weed matt layer and our hugelkultur layer, you can use whatever brown/carbon-rich matter you'd like for this next layer. Options are untreated sawdust, fallen leaves, wood mulch, shredded paper, toilet paper rolls, pea-hay, straw, or small twigs and sticks broken into short pieces.

Autumn leaves are everywhere right now in New Zealand, so they're a good bet.

Spray this layer down lightly with a hose before moving on to your next layer.

Layer 6 - Green

Nitrogen-rich seaweed layer

Throw on another layer of green/nitrogen-rich matter, like grass clippings, blood and bone, animal manure, hedge clippings, used coffee grounds, kitchen food scraps, seaweed if you live near a beach, or sheep dags if you're on a sheep farm. Spray this green layer with a hose.

Layers 7 - 10 (or more)

Wood chips and chicken manure. 

From this point on, just keep layering brown/carbon layers with green/nitrogen layers and giving them a quick spray of water in between until your garden bed is full.

You can leave your garden material to decompose for several months before planting into it, and it won't cost you a thing.

Otherwise, if you want to plant straight away, you could spread a layer of finished compost, topsoil or potting mix over the top of your layered materials and bed your seedlings directly into that.

All the layers you've built will keep breaking down over time until they create rich compost but, because you've been careful about layering nitrogen material with carbon material, none of that action should hurt your seedlings planted above. In fact, the composting action will release fertiliser, invite earthworms, hold moisture and create warmth for your plants.

Please do note that the level of your garden fill will sink over time as the composting action happens, so you will need to keep adding more soil/compost to your garden bed. However, by layering all these gathered resources together, you will form a rich, fertile base for your plants and get your garden off to a wonderful start.

Two gardens full and ready to grow, one garden still filling. 

When I was filling my gardens, I just concentrated on a couple at first, so I could fill them quickly, top them off with store-bought potting mix and start growing vegetables as soon as possible.

I then spent longer filling the rest of my gardens with whatever I could find, but that was great because it meant I always had somewhere to put my grass clippings, kitchen scraps and fallen leaves.

It was fun sourcing my next layer of brown or green material. I was always on the hunt, and I enjoyed that element of it. Waste materials became my treasure trove.

Eventually, however, all my gardens filled up and got planted out. Now they're producing an abundance of food for my family all year round.

This month, I finally got around to building a separate composting area to corral all the same types of materials that I first filled my garden beds with, so that I'll have something free to top up my gardens with each year as they drop. It means I'm back on the hunt for brown and green material again, and I'm loving it.

It's giving me something to focus on during the current quarantine and helps me to see what an abundance of resources I have just lying around.

I hope you found this post helpful. If you have any questions about building a no-dig, layered garden, please feel free to ask them in the comments below and I'll get back to you.

All the best for your gardening adventures! I'm rooting for you. (No pun intended. Seriously. Puns are the worst.)