Today I want to show you a cheap and easy way to make raised garden beds using cardboard. This raised bed tutorial is a no dig gardening method which anyone can do and I will take you through how I used materials I had lying around to make it.
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To build these easy, frugal garden beds, we’re going to sheet mulch. This means we’re suppressing weeds by layering materials which can be broken down to produce nutrient rich soil.
Step 1: Collect Cardboard
Cardboard is a great compostable medium that will suppress weeds allowing you to place a raised bed right on top of grass or weeds. The weeds underneath the cardboard will rot down and provide growing plants with nutrients.
Collect plenty of cardboard boxes to make the bed and try to avoid boxes that are heavily printed with colored inks as these will end up in the soil and often contain heavy metals such as lead or cadmium because they’re colorfast. (If you’re interested in that sort of thing or are a chemist like me, the Royal Society of Chemistry has a great article on Ink Chemistry which they ran in their magazine years ago when I was a student).
It is better to have enough boxes to flatten out and overlap to reduce the likelihood of weeds pushing through.
Step 2: Flatten and position
Flatten the boxes and remove all plastic packing tapes; as the cardboard breaks down, the tape will be left fluttering across the garden or the street which is unpleasant.
Step 3: Add Optional Bulking Agent
I added leaves and dead twigs and prunings to this as a bulking agent and to provide more nutrients as they break down over the course of the growing season. You can use straw, partially decomposed compost, punky wood and shredded paper as well.
The bulking material isn’t necessary you can skip it, I just had a bunch of dry leaves that needed to be put to use. The added benefit of adding fillers or bulking agents in a raised bed is that they can help retain more moisture in the bed; raised beds are often prone to drying out.
The bulking material can also help level out an uneven ground for the plants which will go on top, this particular bit of garden is sloping so it helped to level the new bed with the old.
Step 4: Wet All The Dry Stuff
Wetting the material serves two purposes; one it reduces things blowing away because it is heavier and two, it speeds up decomposition.
You need to thoroughly soak the cardboard and bulking agents you have added on top.
Step 5: Add Organic Matter
I added manure at this point because I’m lucky enough to know people with horses so I can get free manure whenever I need it and it happened to be in a pile waiting to be used. If you don’t happen to have a manure pile lying around, try asking about to see if you can take some. I have found many people here willing to let me take it for free because it costs them so much to dispose of it. Manure will help provide the nitrogen to help break down the cardboard.
You don’t need to use animal manure, if you read the Weblink Wednesday posts you would have seen that there is information now showing that antibiotic use in animals is adversely affecting the soil microbiome. If you don’t have or want to use manure, I would recommend compost, lots and lots of compost.
Once you have piled up the material, you need to level it out and cover the cardboard.
Once it is level, you can add compost or a sowing mix if you plan on sowing seeds directly to give them the best kickstart.
Step 6: Optional Amendments
I like to add certain soil amendments to the raised beds I’m creating namely dried kelp (pictured above) or seaweed and rockdust to help remineralize the soil and to provide the plants with additional nutrients as they grow. You can also add things like guano, worm castings, biochar or chicken manure pellets if you are concerned about the cardboard or bulking agents robbing the compost of nitrogen for the plants to use.
Follow the directions from the manufacturer on useage rate and sprinkle on the bed and lightly rake to distribute the material.
Step 7: Edge
Once you have leveled off the compost and raked in any soil amendments, you can edge the bed to make it look pretty using bricks, stone, bottles, wood or decorative edging.
I opted to leave the bed unedged for the moment whilst I continue to extend the vegetable garden across the side yard.