What is the cardboard weed barrier method?
Starting a garden bed can feel like standing in front of a puzzle with no picture on the box. You have the plants picked and the tools ready, and then there are the weeds, which turn up whether or not you invited them. The cardboard weed barrier method is the cheapest way I know to deal with them, and it uses something you are already throwing out.
What the method is
You lay plain cardboard flat over the soil, wet it down, and cover it with mulch or compost. The cardboard blocks light, so the weeds underneath give up, and because it is only paper it breaks down over a season and feeds the soil on its way out. No chemicals, no plastic weed mat left in the ground in ten years time.
That last part is the real advantage over a synthetic weed mat. Plastic matting works and then it stays there, going brittle and tangling in your fork every time you dig. Cardboard does the job and then leaves.
Why it suits a beginner
- No special tools. Flattened boxes, a hose, and something to cut with.
- It costs almost nothing. Most households have a stack of boxes waiting to go out.
- It feeds the soil. As the cardboard breaks down it brings worms up under it, and worms do the digging you were going to have to do.
How to set it up
- Gather your gear. Flattened cardboard with the tape and staples pulled off, a box cutter, mulch or compost, and a hose.
- Cut the weeds down. Knock the existing growth over rather than digging it out. It does not need to be tidy, because it is about to be smothered.
- Wet the soil. Damp ground underneath helps the cardboard settle and start breaking down.
- Lay the cardboard. Overlap the edges generously, because any gap is a gap a weed will find. Cover the whole bed.
- Soak it. Wet the cardboard properly so it lies flat and stays put instead of blowing across the yard.
- Mulch on top. Five to ten centimetres of mulch or compost. This holds it down, holds moisture in, and stops the cardboard looking like rubbish.
- Plant through it. Cut a small hole where each seedling goes, straight through the cardboard into the soil below.
The questions people actually ask
- Does the type of cardboard matter? Plain brown is best. Skip anything glossy, waxed, or heavily printed, and pull off the tape and the plastic labels.
- Will it hurt my plants? No, as long as you cut proper holes for them rather than expecting roots to push through it.
- How long does it last? Usually a season, sometimes a bit longer in a dry spot. By the time it has gone the mulch above it has settled in and is doing the work.
- Will it stop every weed? It stops the seedlings and most of the annuals. Deep rooted runners like couch and kikuyu will find the edges eventually, so watch the perimeter.
Shop related products
- Martins Organic Sugar Cane Mulch Bale. Light, easy to spread and it breaks down into the soil.
- Martins Organic Pea Straw Mulch Bale. Adds a bit of nitrogen as it rots, which suits a veggie bed.
- Naturally Good Mushroom Compost 25L. Good as the layer straight on top of the cardboard.
- Brunnings Garden Compost with Seaweed 25L. For working through the bed before you start.
Did you know we also keep bulk mulch, straw bales and soil conditioner in store, and not all of it makes it onto the website. Give us a ring on (08) 8536 4333 to check what is on the shelf.
The mulch and compost are in the garden centre, and if you tell us the size of the bed we can work out roughly how many bags you need rather than you guessing and going back twice.
Keep reading
- What organic products can I use to fertilise my lawn
- How do I plant a tree
- 5 easy to grow tomato varieties for beginners
Cheers,
Candeece
I once laid a whole bed without overlapping the edges and grew a very tidy grid of weeds.
