What the heck is sheet mulching?

We had a question from our post, 10 Things I learned last summer and should try to remember for this year…, regarding the first lesson we learned last summer. The question posed was about a vague statement I made about cardboard on top of grass. I feel like a bigger explanation is in store. Three years ago, I didn’t know what sheet mulching was and I’m so glad I found out. It has saved so much time and energy and created so much organic matter in our garden beds.

What is sheet mulching?

Sheet mulching is the practice of placing cardboard or layers of paper on top of your existing lawn and then covering it with organic matter.

What type of organic matter is best?

A mixture of organic material is best to get a range of nutrients. You can use compost, shredded leaves, grass clippings, non-diseased plant material, triple mix (compost, manure and peat combined), well-aged sheep or horse manure, or garden soil mixed with compost or triple mix. Many of these options are available at your local nursery.

Why is sheet mulching a good idea?

By sheet mulching, you are creating layers of fresh organic matter through the decomposition of the grass and cardboard. If you were to just strip the layer of grass (or sod) away, you’d be taking with it a multitude of organisms that live in the soil and help maintain the proper nutrient balance. Sheet mulching keeps the nutrients there and adds more.

When is the best time to sheet mulch a new garden bed?

Ideally, you’d like a few months of decomposition before you direct seed or plant your garden. We’ve waited three months and the plants had no problems establishing strong root systems as the cardboard was well on it’s way to being soil by that time.

Will sheet mulching kill everything underneath?

It kills the grass and weeds underneath, but the organisms that need air and sunlight make their way through the cardboard (that’s why softening it up with water is a good idea) and in doing so, break that cardboard down into smaller and smaller bits, thus creating the organic matter.

What are the steps to sheet mulching? 

  1. Determine the location and size of your new garden bed.
  2. Use an edging tool to edge around new bed. This step is optional, but it creates a nice end point for the cardboard. Throw edging bits into bed where they can add to the organic matter.
  3. Cover every inch of the garden bed with cardboard. Using cardboard with coloured ink can leach unwanted chemicals into the ground, so try to use only black ink or blank boxes. Be sure to overlap your cardboard pieces so you can’t see any grass underneath.
  4. Thoroughly soak the cardboard. This softens it up, making it easier for those worms underneath to find their way through it.
  5. Cover the cardboard with 6-12 inches of soil. We don’t create enough organic matter here so we have to bring it in from the local nursery.
  6. Be patient while the grass and cardboard decompose. Thank the worms for their hard work.

 

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This was after Steps 1 & 2. You can see all the edging bits thrown into the bed. On this bed, I didn’t put down cardboard at all. Lesson learned: grass and weeds will grow through many inches of soil – do not skip the cardboard step!

Unfortunately, I didn’t take any pictures during our garden installation of the cardboard being laid down. But this was the finished product in Phase 1 of our garden:

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Properly sheet mulched garden installation. That equipment in the background is not ours. The dog in the front? Yep!

I hope this answered some questions. This is one lesson I’m glad I learned. I’m unhappy I didn’t follow it for a summer and happy to share my mistake with you if it helps you in your gardens.

 

 

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