Organic Gardening: How to use Black Plastic to Kill Weeds

Organic Gardening: How to use Black Plastic to Kill Weeds
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Black plastic laid on the ground will kill weeds

Once the excitement of starting a new garden wears off for beginner gardeners, the questions begin. One of the most common is ‘What’s the first step?’. How do I convert a piece of lawn or overgrown allotment into a productive garden? The best way to start is to remove the vegetation and especially the perennial weeds. If your goal is to grow organically, there’s an easy way for you to do this — suppress the weeds with Black Plastic Sheeting.

Organic Gardening: How to use Black Plastic to Kill Weeds

How to clear land using black plastic

  • Mow the area or strim it so that the weeds and plants are low to the ground
  • Lay heavy duty Black Polythene Plastic Sheeting on the ground and weight it down
  • Leave for 2-3 months in summer or six months in winter
  • Lift the plastic, remove slugs, and dig up perennial weeds
  • Dig over the soil and prepare it for planting

Organic Gardening: How to use Black Plastic to Kill Weeds

Plants can grow under blue or light coloured plastic

I’ve gradually been settling into my new allotment plot but one corner of it is still unused. To help get it ready for growing, I’ve covered it and the compost pile beside it with a layer of heavy duty black plastic. This is the kind of stuff that you’ll find as pond or roof lining and will hold out well in the elements.


Thin black plastic, like bin-liners (garbage bags) are not suitable since they rip and shred and will cause a lot of litter. Blue tarps and light coloured plastic isn’t great either since some plants will still grow under it.

Organic Gardening: How to use Black Plastic to Kill Weeds

Leave the plastic on the ground for 2-3 Months

Once the plastic is laid out and weighed down, you just leave it and let it do its work. Because the dark colour stops sunlight from getting to the plants below, most of the plants die off. Grass and annual weeds are the first to go but hardier weeds can take longer. In warmer months it can take as little as two months for the plants underneath to die and rot down. In winter leave the plastic for around six months.

Some weeds will survive the apocalypse and even after a year of being covered, the Dock on my plot is still alive. They show up as white and yellow stems as I lift up the plastic so they’re easy to spot and dig up. Slugs and other pests are easy to see when you lift the plastic too. Take the time to remove and destroy them and you’ll save yourself the pain of them multiplying and eating your veg.

In case you were wondering, the plastic only dries the soil out when used in very large sheets. In smaller areas, like the one I’ve just dug over, the soil is moist and worms and other animals are unaffected.

Organic Gardening: How to use Black Plastic to Kill Weeds

Dead plants can be dug back into the soil

After an hour of digging over the patch the area is good to grow! The dead plants and leaves left on the surface can be reworked back into the soil. However, the living perennial weeds including Dock and Creeping Buttercup need to be manually removed. I take mine to the city’s green waste bin and sometimes just bin them.

Dock is my particular garden foe and I’ve gotten to know this plant well over the years. The smallest piece of its root can sprout a new plant and in an ordinary compost pile they continue to grow. Be careful of where you dispose of it. Throw it to the side of your garden and it will set seed and recolonize your garden in no time.

Organic Gardening: How to use Black Plastic to Kill Weeds

A new raised bed in an area that was once weeds

In an area that was just weeds is now a brand new raised bed. I used timber salvaged from my old plot to build it and the inside is filled with soil and rotted mushroom compost. Later this week I’ll be attempting to transplant some established asparagus plants into it.

You don’t need to convert land into raised beds afterwards — that’s just my choice since I garden on a slope. What you will need to do is add organic matter such as garden compost, rotted horse manure, rotted mushroom compost to the soil. You can lie this on top and let the worms do their work. If you’re like me and have the New Zealand Flatworm in your garden you’ll probably need to dig it in a bit. New Zealand Flatworms have decimated my worm population.

From weedy land to garden bed, all it took was black plastic, a bit of time, and a fork over. If you’d like to clear land the organic way, this is the easiest way to go. For other ideas on natural weed killer ideas head over here.

Organic Gardening: How to use Black Plastic to Kill Weeds

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8 Discussion to this post

  1. Joie Parris says:

    Hi, I have bindweed in one of the beds I’m doing this with. We haven’t lived here long so we didn’t know we had bindweed in there before we filled the bed with strawberries and soft fruit bushes 🙁 We’re now moving all the fruit into pots so we can deal with the weeds, but is bindweed one of the things that will survive black plastic? Will we still need to dig it out as well? Thanks

  2. Myra says:

    What mil do you purchase to kill weeds 1 mil, 2 mil, 3 mil

  3. John says:

    This is great information thanks for sharing! Have a couple of weedy areas in my garden that I’ve just covered over so hopefully in a few weeks I’ll have gotten them all.

  4. Cannon White says:

    I recently got into gardening and have been wondering the trick for this. Great read!

  5. An excellent post. You’ve explained the technique and your use of it very clearly. I live in NZ and have seen a variety of the endemic flatworms (there are thought to be be more than 100 species) but didn’t know what they were and have let them be. The one you describe is probably Arthurdendyus triangulatus (Artioposthia triangulata) (source Judging by the number of earthworms in my garden it’s not living in this area. If you destroy them, make sure you don’t leave any bits behind because they can regenerate any parts they lose. Nasty pests, not to be taken lightly, it seems.

    • lovelygreens says:

      It’s actually the Arthurdendyus triangularus that we suffer from — horrible things. Glad you don’t suffer from any earthworm loss even in NZ. I often wonder if it’s a different species of worm(s) you have down there and if that’s why they’re not affected.

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