Sheet Mulching

Garden - Sheet Mulching - Sheet Mulch 01

“Sheet mulching is one of the best things you can do for your yard or garden!”

Sheet mulching is the practice of covering an area of land with a blanket layer of biodegradable material, which blocks grass and weeds from getting sunlight, and prevents moisture from evaporating out of the soil. If you have an area of land that you’re not using, or would like to use in future, sheet mulching is the perfect thing to do.

Benefits:

  • Saves water
  • Blocks weeds
  • Covers grass
  • Improves soil

Materials:

  • Cardboard (lots of big sheets)
  • Mulch (free mulch is the best mulch!)
  • Other soil amendments

Jump to:

Sourcing Free Mulch
Sourcing Cardboard
Choosing soil amendments
How to Sheet Mulch
Follow-up Maintenance
Watering
Planting Through Sheet Mulch
FAQ
What else can I use to sheet mulch?
How long will it take for grass and weeds to die?
Grass and weeds are coming through my sheet mulch. What should I do?
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Mulching

Sourcing Free Mulch

Free mulch is the best mulch!

A blanket layer of cardboard covered with free mulch.

Free mulch is the best mulch! It’s the stuff tree-loppers amass in their trucks and have to dump into landfill. It’s a mixture of coarse and fine wood chips, twigs and shredded leaves. It’s also usually made up of material from different trees. All of this variety stimulates soil life, and while smaller particles are breaking down into fertiliser, larger pieces continue to serve as mulch. The best part about it – it’s free!

Start calling up your local tree-loppers, and let them know that you’re happy for them to dump mulch on your property. Ask them to give you a phone call before they dump. Some loppers prefer to dump their truck first thing in the morning before their day’s work, whilst others prefer to dump at the end of the day, and all of them prefer to fill their trucks before dumping, so be ready for 7 cubic meters or more!

If your property is a little too far out of their way, consider offering to pay for their fuel, or if you’re in Australia, just offer them a carton of beer!

Sourcing Cardboard

A blanket layer of cardboard, laid out like roof shingles so no light can get through.

A blanket layer of cardboard, laid out like roof shingles so no light can get through.

Plain cardboard boxes are used by many businesses for transporting stock. For sheet mulching, large sheets of cardboard make the job easier. Ask around shops which sell refrigerators, televisions, flat-pack furniture, bicycles or musical instruments. You can also find a range of different sized cardboard boxes from hardware stores and grocery stores. You will need enough cardboard to cover the intended surface PLUS more, as you will need to overlap them like roof shingles.

Choosing soil amendments

Just before you sheet mulch, you have a great opportunity to amend your soil with compost, worm castings, bentonite clay or gypsum (if you have sandy or clay soil, respectively), lime or sulphur (if your soil is acidic or alkaline, respectively), rock dust and other trace minerals, and you can even spread weeds and other plant material over the surface before you sheet mulch. All of this will gradually decompose and work into the soil.

How to Sheet Mulch

If you've laid your cardboard like shingles, you can push mulch over it easily

If you've laid your cardboard like shingles, you can push mulch over it easily

  1. Lay collapsed cardboard boxes down over the area you wish to sheet mulch. Imagine you are laying roof shingles – the boxes should overlap each other on all sides. The idea is to block all sunlight from getting through to the weeds and grass below. I recommend overlapping them in a consistent fashion, to create a ‘grain’ or ‘flow’ for mulch to spread over.
  2. I also recommend extending the cardboard layer over the edges of the area of land, to limit the amount of sunlight that can get into the sides and permit weeds and grass to grow.
  3. Around plants and trees, you can tear cardboard into all sorts of interesting shapes and wrap them snugly around stems and trunks.
  4. Dump mulch onto the cardboard, being careful not to shift any of the boxes. Spread the mulch (with the ‘grain’) over the cardboard thickly and evenly. You can go as thick as you like. I recommend spreading the mulch right over the edges of the cardboard, to cover the cardboard completely, and further block sunlight from entering the sides.
  5. Spread the mulch around plants and trees but leave a small gap, so the cardboard can still be seen. If the trunks/stems get wet they may rot, so you want the cardboard to dry quickly around them.
Lay your mulch right over the edges of the cardboard, and lay it as thick as you want.

Lay your mulch right over the edges of the cardboard, and lay it as thick as you want.

Follow-up Maintenance

Around the edges of your sheet mulch is always the most vulnerable to sunlight, and even a thick sheet mulch may let a few grass shoots through. These mustn’t go unattended, because they are now in a perfect environment to thrive!

After a few weeks, it's easy to see weeds and grass escaping

After a few weeks, it's easy to see weeds and grass escaping

After finishing your sheet mulch, wait a few weeks, then check if any weeds or grass have appeared. Get yourself a small bottle of herbicide and pour a tiny amount into a tray with water, and use a paintbrush to paint the mix onto the weeds and grass. It’s recommended that it’s given 6 hours to absorb, which means make sure it doesn’t rain or get watered in this time. Herbicide is horrible stuff, and it will make its way down into the plant and kill the whole thing root to tip.

Whatever you do, don’t spray the mix! If any of it gets on your beloved trees or plants, it will seriously damage or kill them. Worse still, inhaling the stuff or getting it on your skin can cause serious damage to you (wear gloves!).

Be careful not to get any weed killer on your wanted plants!

Don't get any weed killer on your wanted plants. It will kill anything it touches!

It’s unfortunate that we use harmful chemicals like this, but if you sheet mulch thoroughly, and cover all areas where grass might enter, it’s likely you’ll only need herbicide once.

Watering

There’s no need to water your sheet mulch. It is simply a blanket covering grass and weeds, and it will serve its purpose without watering. If you decide to plant trees or plants through your sheet mulch, I recommend watering immediately around the plant only, and leaving the rest of the mulch dry. A dry sheet mulch will last much longer than a moist one, and you’ll need your mulch (especially the cardboard layer) to last long enough for all the grass, grass seeds, weeds and weed seeds to break down – this can take more than a year!

Inevitably the rains will come and wet your sheet mulch. This is fine, but consider the impact your feet have on softened cardboard – if it tears, grass and weeds might get through. Try to avoid walking on wet mulch.

Planting Through Sheet Mulch

You can immediately start planting through your sheet mulch, once it is laid.

  • If you’re planting young trees, consider preparing cardboard potholes for each of them.
  • If you’re planting seedlings or hardy shrubs, just stab a hole through the mulch and plant their roots below. I recommend watering just these spots, and not the whole sheet mulch.

Frequently Asked Questions

What else can I use to sheet mulch?

You can sheet mulch with anything biodegradable!

  • For the blanket layer, you can use newspaper, hessian bags or bed sheets instead of cardboard. Wool carpets are usually filled with fungicides and insecticides, and are not a good choice for sheet mulching.
  • For the coarse mulch material you can use almost anything! Just make sure it’s not weeds, grass clippings or soil with weed seeds in it, or you’ll have weeds and grass growing wild!

How long will it take for grass and weeds to die?

For existing grass and weed plants, the longest time needed is 1 year (for Kikuyu grass). However, some plant seeds can remain dormant for years, waiting for appropriate conditions to sprout. Consider the plant types in your area, and remove any that you think might persevere.

Grass and weeds are coming through my sheet mulch. What should I do?

Either your blanket layer was not sufficient to block out light, or grass and weed seeds have found their way into your mulch. If it it’s the former, consider scraping back your sheet mulch and starting again. If weed and grass seeds are always going to blow in, consider managing them in another way (keep your soil soft, so you can pull weeds out easily – roots and all). I recommend you don’t get into a habit of using herbicides regularly – they’re nasty!

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“Make your soil as healthy as a forest floor, by mulching!”

 


 

 

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