Black plastic mulch can kill grass and weeds to make space for a vegetable garden. It’s an eco-friendly way to clear land without having to use herbicides.
Once the excitement of starting a new garden wears off, the questions begin. One of the most common is ‘How do I convert a piece of lawn, or overgrown allotment, into a productive garden?’ The best way to begin is to remove any unwanted features and vegetation, especially perennial weeds. If your goal is to grow organically, there’s an easy way for you to do this — kill weeds with black plastic. The technique is called sheet mulching, and once you lift the plastic, your land will be clear for cultivation.
This is exactly how I created my own vegetable garden and it saved me an incredible amount of time and energy. It’s the main way that I recommend clearing land without using herbicides since it’s suitable for organic gardening and also, pretty easy. The before and after photos below show how I covered the entire area and then gradually peeled the plastic back. Bit by bit I transformed a weedy plot of land into a beautiful and productive veggie patch. You can see more of my garden, and learn about two other types of sheet mulch in the video at the bottom of this piece.
Black plastic sheeting cleared this plot of weeds and grass. It made creating a new vegetable garden easy and eco-friendly.
How to clear land using black plastic
- Mow the area or strim it so that the weeds and plants are low to the ground. Remove any visible perennial weeds.
- Apply a 2-3″ layer of organic compost (optional)
- Lay heavy-duty black polythene plastic sheeting flat on the ground and weight or peg it down.
- Pop fine holes in the plastic to allow air and moisture through (optional)
- Leave for 2-3 months in summer or six months in winter
- Lift the plastic, remove slugs and New Zealand flatworms, and dig up perennial weeds
- If you’ve not applied organic compost first, you will need to apply a good layer now. Plant directly into the compost and you’ll get a crop that very first year.
No need to break your back digging weeds out. Just cover the soil with black plastic to kill weeds.
Heavy-Duty Black Polythene is best
After clearing most of my plot using this method, I had just one last weedy corner to tackle. The photos in this piece are from that corner, and to help get it ready for growing, I covered it, and the compost pile beside it, with a layer of heavy-duty black plastic. This is the kind of material that you’ll find used as pond or roof lining and will survive the elements. Thin black plastic, like bin-liners (garbage bags), is not suitable since it easily rips and shreds. Blue tarps and clear or light-colored plastic aren’t great either since some plants will still grow under it.
You can get heavy-duty black plastic (polythene/polypropylene) sheeting in other colors. I’ve seen it in a light blue color before and this is also fine for using to kill weeds and clear land. It can be more of an eyesore than black, but if it’s thick enough, no light will get through it either.
After a couple of months of being covered, this area is nearly completely free of grass and 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 color 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 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.
Only the hardiest of perennial weeds can survive. They’re easy enough to dig out afterward though.
Dead plants can be dug back into the soil
After removing any last weeds, the ground under the plastic could be ready for immediate planting. That is, if you’ve applied a layer of organic compost to the ground before you put the plastic down. If you haven’t, you can apply it to the bare soil now. The best way is as a 4-6″ layer of mulch, to create a no-dig garden. That mulch will also cover any seeds that are lying at the soil’s surface and will stop them from germinating.
You might also spot dead plants at the soil surface. Desiccated or slimy grass and weeds. Apply the mulch directly on top of them since they won’t grow. Worms and other soil bacteria in the compost will break them down into nutrients in no time at all. If the plants look fleshy still, then they could still be alive. That was the case with dock weed in my garden and I manually dug them, and their long taproots, up. Any tough weeds like that I put into a container and either dispose of them or leave them to eventually break down.
The beds after digging up the last perennial weeds
Cons of using black plastic to kill weeds?
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 soil creatures seem unaffected. There’s also, information floating around on the internet about how plastic sheet mulch can negatively affect soil organisms and the garden. If any reduction of soil life does occur, it is only temporary, as I and many others have seen in a real-world scenario. The study that folks refer to is one conducted by Washington State University; a study that may be flawed due to the testing method.
Regardless of any studies, sheet mulching with black plastic works well to clear the land and help create an organic vegetable garden. I just wouldn’t recommend that you use it as more than a temporary solution. If you wanted to use something to protect the soil of beds each winter, cover with a material that’s durable but light and air-permeable. Something like landscaping fabric. If you use the plastic woven mesh type, just make sure to melt the edges with a lighter or creme brulee torch. If you don’t, it will shred and turn into a mess.
A new garden bed in an area that was once weeds
In an area that was just weeds is now a new slightly raised bed. I used timber salvaged from my old plot to build it and filled the inside with soil and compost. You don’t need to convert the land into raised garden beds afterward — that’s just my choice since I garden on a slope. What you will need to do is add a 3-6″ layer of organic matter such as garden compost, rotted horse manure, and rotted mushroom compost to the soil. You can simply spread it on top and let the worms do their work. From weedy land to garden bed, all it took was black plastic, garden compost, and a bit of time.
Another great thing about using black plastic sheet mulch is that it can be reused many times over. Use it to extend your garden, or lend or sell it on to other gardeners. At our allotment site, we cover any vacant plots with black plastic and some of it is five years old. When you kill weeds with black plastic you’re saving effort and starting your new garden in an efficient way.
My garden now after first clearing it with black polythene sheeting
How to kill weeds with black plastic
Equipment
- Black polyethylene (polythene) plastic sheeting
- Large stones, weights, or pegs
- Garden fork
Ingredients
- Organic compost
Instructions
- First, clear the area that you'd like to turn into a vegetable bed or entire vegetable garden. Cut the grass short, and dig up any shrubs or perennial weeds.
- It's best to next lay two to three inches of organic compost on the ground. You can also spread the grass clippings, leaves, and any other finely chopped organic material. If you don't lay this layer, the ground will be bare soil when the process is finished and will need more work.
- Spread the black plastic sheeting over the entire area you wish cleared. A second person helping will make this step easier, and avoid laying the plastic on a windy day.
- Weigh the plastic down at all four corners, along the edges, and throughout the center. Ensure that wind is not going to pick the plastic up and send it sailing to the next county.
- If you'd like to increase the amount of air and moisture reaching the soil beneath, pop small holes in the plastic with a pitchfork/garden fork. Doing this can help the soil biota beneath.
- Leave the plastic in place for however long it takes to kill the grass and weeds underneath. In the summer it may only take two to three months, in the winter it can take double that. If you have a lot of tough weeds underneath, it may take up to a year.
- Peel the plastic back, either all at once or a part at a time, to begin growing in your new growing space. If you've laid compost down first, the ground will be tilled by worms and soil bacteria and ready for planting.
- Watch the video below to see how to use heavy-duty black plastic to kill weeds, alongside two other types of sheet mulch. Shows further before and after shots.
Notes
Can you please tell me what type/size wood you have used for your beds?
I have a piece sharing how I built my raised beds in the home garden here https://lovelygreens.com/building-raised-garden-beds/ but the wood I used in the allotment is different. It’s really whatever I could get on the cheap from our local saw-mill and isn’t consistent in size or shape. It’s all rough-cut and untreated soft-wood though.
Hi. I am tired of digging up weeds so was looking into alternative ways to deal with them and was reading about the black plastic. One of the sites where I read about this said laying plastic down wasn’t the best idea because the chemicals from the plastic leached into the soil. Makes sense but is this really something that happens?
Using polythene sheeting in the garden is perfectly safe. Though polythene could potentially (although very unlikely) leach Bisphenol A in the soil, it has a half-life of less than a day and is not a concern.
When you use clear plastic to kill weeds you’re supposed to soak the area with a hose pipe before covering. Do you do the same with black plastic? Or do you just lay it straight down? Thanks
Weeds will continue to grow under clear plastic so you really need dark plastic to kill weeds. And no, you do not need to soak the ground beforehand.
I’m a novice gardener and learning so much this year. Very expensive education, I might add… I read your blog article and wondered if using billboard vinyl might work? Some companies throw this used vinyl away so I might be able to get some for free. If I put compost down in late fall and covered it with billboard vinyl until spring, do you think that might work? Or would it breed fungus into the soil? Thanks!
I’ve never worked with that material so am unsure about whether it would be suitable or not. For example, the inks used might not be food-safe and the material might break down in strange ways. I’d experiment with a small strip but not cover an entire garden with it at first.
Thanks so much for this post. I’ve just started paying attention to the lawn in front of my rental, and it is absolutely covered in all kinds of weeds, including the incredibly invasive Buckthorn! I think smothering everything is the best bet, but I’m wondering if there is a way to save the beautiful peonies that are managing to flourish in spite of all the weeds. Can I cover the ground around the peonies, or would that defeat the point? There are also a couple of bushes in the space, and I’m wondering if I can cover the ground around them, or they also need to be cut down to stumps and covered. Thanks!
You can of course cover the ground around the peonies. If you’re using this technique in your front garden, I’d advise that you pretty it up so that everyone in the neighborhood is happy. Covering it in wood chips (you can often get it free from tree surgeons) will hold it down and look nicer.
Hiya,
I wanted to ask about using cardboard (and white cotton-like fabric) instead of black plastic – as well as using dead weeds as the organic layer under cardboard.
Short version of my situation – I’m laying down sheets over very large areas of what used to be flower beds but ended up being dominated by various weeds and bramble (now all dug up). I accidentally left some weeds in a large plastic bag for weeks and it’s turned into a mess and oozing black liquid. I wondered if I could use this as the organic layer UNDER cardboard (with compost on top). The flower beds are also full of dead wooden bramble shoots and twigs – can I leave this under the cardboard or do I need to clear it? How much is too much?
The white fabric you’re referring to is called fleece. You can use cardboard to suppress weeds but it will degrade very quickly thanks to weather and worms. Fleece won’t do the job because weeds will happily grow under it. It’s best to use heavy-duty plastic. As for the decomposed weeds — I’d dilute the liquid in water use it as a plant feed. Put the rest on the compost pile.
It’s March right now. Is it too late to kill all the weeds and grass by this spring for a garden? Thanks!
It’s probably too late for a spring garden, but you could lay it and have the ground clear for summer plantings.
Thank you so much!! Was looking for information just like this for my gardening project.
Will the plastic need to be one continuous piece (not allowing any water through whatsoever), or can I roll out three or four strips (overlapping one another by a foot or two) of 10’x30’ plastic sheeting to cover my 30’x30’ plot?
Overlapping is fine BUT they have a tendency to get ripped up by the wind a lot easier. Use a lot more weights at all seams and you should be fine though.
In a garden covered with black plastic and compost how to does the water get through to water the plants when they’re planted in the plastic. I see flower beds with compost and plastic peeking through planted with flowers, but I don’t know understand how the water gets to water the plants.
The flower beds you’re referring to are likely planted over landscaping fabric. It’s a fabric or plastic mesh that’s permeable to water. This piece is not about using that type of material but a solid plastic sheet to exclude light and kill all plants underneath.
Hi, was just wondering how you recommend disposing of the plastic afterwards? I’m a little reluctant to buy new plastic. Thanks!
We don’t dispose of it — it folds up easily and can be used again on new ground. You can use it yourself or pass it on (or sell) to another gardener.
Thanks for the info on killing of weeds with plastic sheeting. Sadly, my backyard has been completely overrun with buttercup. I’d like to try this method, but I’m wondering if there are any issues with the nearly constant winter rains (and sometimes snow) we get here in Seattle. Did you have any problems with water building up on the surface? Also, are there any additional hints for making sure I totally remove any parts of the buttercup that might allow it to get re-established?
The ground underneath tends to stay dry and unless there’s dips in the surface, I don’t see water build up being an issues. As for re-establishment, make sure you cover all the buttercups and you’ll be good. If they’re invading from a neighbor’s land, then you might want to consider some sort of barrier.
Using several layers (6+) of newspaper with some mulch over them is a more environmentally acceptable solution. They break down and the earthworms love newspaper.
I have heard that black plastic is bad for the environment and that it can seep lead and bromine into the earth. Does anyone know anything about this?
Thanks!
The plastic that this thought refers to is the type used to make bin liners (garbage bags) and black plastic for electronics. Polythene sheeting is safe for the garden.
Wow. Your garden looks stunning!
I´ve been thinking about going for the black plastic for a while but couldn´t decide because of course petrol is used in the making of it. However, comparing the life of the heavy duty black plastic versus the tractor that plows the field, or even the energy of your own back relentlessly digging out weeds, the plastic is a nice solution.
It should hopefully last for years to come, too.
If I cover it now (I bought 0.40 acres in Arkansas), will I be able to catch a growing season next year? Maybe I’ll cover half the fields, farm the other half (and weed out with tools), then in late summer/fall farm the other covered parcel?
Yes. Get it covered now and better yet, mow, cover with manure, then cover. If you do that, you’ll have ready made beds in time for late spring planting.
Here in the US, we are in the last month of summer. The soil is moist. If I cover the soil now with thick black plastic and leave it the entire winter, do you think the weeds will die?
Thanks
NV
Absolutely. It takes longer for plants to die under plastic in the winter but a good few months will do it.
Where can I get the black plastic from to kill weeds
There are some links in the piece that will direct you to where you can purchase it on Amazon.
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
All plants will die under black plastic given enough time.
When you say all plants, do you also mean it could keep nandena from growing back?! We usually just run over it with the lawn mower to keep it down. Poison only works on fresh cut branches. Nothing kills the roots, they just keep spreading.
Heavy duty black plastic will kill most shallow-rooted weeds — both annuals and perennials. Nandena is an evergreen with a deep taproot so will probably need digging up.
I’m in Northern California – Hot Mediterranean, Zone 9B (actually just below the Carr Fire going on right now). We did some earth moving and cover cropped the area we are looking to occulate. All of the cover crop has died back and its basically the dried oats that are still standing – which we plan to weed-eat down before occulation. We will likely have no rain until October. Do you recommend wetting the area down before applying plastic (after we chop the dry grass down)? Thanks! ~Heather
Hi Heather, if you’re not planning on growing anything in the soil until spring then I’d wait until the soil is moist before covering it. The reason being that covering dry land and dry vegetation will most likely leave you with dry soil and mummified weeds when you lift it back up. In warmer climates it only takes about three weeks for everything under the plastic to die off and be pulled back under the soil by worms. Without that moisture, worms won’t find the soil underneath very hospitable.
What mil do you purchase to kill weeds 1 mil, 2 mil, 3 mil
The thicker, the better!
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.
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 endemic flatworms (there are thought to 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). 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.
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.
The black plastic, I’ve tried all over to get some but being quoted stupid prices can you point me in the right
direction?
I’ve provided a link in the piece to where you can order it online