Clearing land for new garden space can be truly back-breaking work. Use these tips for how to use the power of sunlight and black plastic to kill weeds instead. The method uses no chemical sprays, is easy to do, and keeps the soil structure intact. Once the plastic has had time to work and peeled back, you’re left with a clean slate of cleared land that you can begin growing on immediately. It’s an eco-friendly way to clear land without having to use herbicides.
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Once you decide that you’re going to start a new garden or garden bed, the questions begin. The big one is usually around figuring out the best way to convert a lawn into a productive garden. It’s clear that you can’t plant directly into it since grass will outcompete crops. The soil probably also needs amending with organic matter, and to do that, all the vegetation must be removed. One way or another, you’re going to need to clear the land of everything currently growing on it. Instead of hacking away at turf or double-digging, the way that I recommend doing it is to use black plastic to kill weeds. It’s far easier and more effective than the alternative.
This is exactly how I created parts of my last two vegetable gardens and two large flower borders. Doing it this way saved me an incredible amount of time and energy! Using black plastic is the main way I recommend clearing land without using herbicides since it’s easy and suitable for organic gardening. The before and after photos below show how I covered an 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.
Traditional Methods for Clearing Land
In the past, most people would go about clearing land by lifting the turf from the soil, double-digging, or tilling it. The first method is labor intensive and involves cutting squares of turf, lifting each piece off, and stacking them somewhere to break down. Unfortunately, that also means that the nutrients that are in that sod are taken off too. Double-digging means digging the soil to around three feet and burying the sod and weeds at the bottom.
Tilling with a cultivator as farmers do, or with a rototiller, is another traditional way to clear land. While it can be quick and effective, it has drawbacks. Weed seeds long buried under the soil surface are brought up where they can grow. The roots of pernicious weeds, like dock and bindweed, can also be chopped up. Each piece has the potential to regrow into a new plant, which could mean a challenging weed problem in the future.
I’ve seen this happen to an allotment garden before. It was a bare field, to begin with, and instead of temporarily sheet mulching it with plastic, as I explain further below, they had it plowed. Though the soil was at first bare, it didn’t stay like that for long. Within weeks, the entire area regrew into a solid mass of dock weed, and the problem was so big that the land was later abandoned.
Another drawback of tilling is that it breaks up the soil structure, which can have repercussions on how moisture-retentive and alive the soil is afterward. That’s because plowing destroys soil health and the fungi network that plants need to grow to their full potential. There’s an entire soil microcosm beneath our feet that most people aren’t aware of!
Sheet Mulching to Start a New Garden
When I started my very first garden, I double-dug it. It was extremely hard work, and when I look back, I shake my head at myself. I’d not heard of no-dig gardening back then and was only following advice I’d learned from more experienced gardeners. I now practice no-dig, which means I don’t turn over the soil when I start a new bed or turn the soil at any other time of the year. Instead, I spread compost over the soil and call it a day. My over 200,000 YouTube subscribers can vouch for me that it works!
Using black plastic to kill weeds is often the first step in creating a new no-dig garden. However, it’s an excellent method for clearing land, no matter what type of garden you plan on building. A traditionally dug garden, raised beds, or a no-dig garden. What it involves is cutting the grass and weeds down as best you can. Then you cover the area with thick, dark plastic sheeting, weigh it down, and allow it to suppress growth and eventually kill everything that was growing underneath it. Even perennial weeds. This technique, a temporary form of sheet mulching, works through light exclusion and soil polarization. The thickness of the plastic makes it dark, and plastic traps heat and creates a kind of greenhouse effect underneath.
The Type of Black Plastic to Use
It’s really easy to clear land using black plastic, and I’m going to lay it out for you below. Before you begin, you will need heavy-duty black plastic sheeting large enough to cover the area completely. It can be all one piece or layered in a way so that plants cannot grow through. This polythene plastic is thicker than garbage bags and is sometimes called Visqueen. It’s so thick that light cannot pass through it and won’t rip very easily, either. Typically, the black plastic you use to clear land should be at least a 1000 g gauge, so it’s pretty thick.
Though I say black plastic, I’m referring to the usual color of Visqueen. I’ve seen it in other colors, including light blue, which will work as long as light cannot get through it. That’s because plants need light for photosynthesis; if it’s excluded, they die. That’s what you’re aiming for! If you use plastic sheeting that allows light through, then the plants underneath will not die. That’s the case with using standard blue plastic tarps or clear plastic. If the plastic is too thin, then some plants can push through it, and the plastic can rip and degrade in the elements.
How to Use Black Plastic to Kill Weeds
Mow the area so that the weeds and plants are low to the ground. You can leave the grass and weeds in place as long as there are no seedheads or flowers, like dandelions. Remove any visible perennial weeds that you can spot by pulling them up or individually digging. Next, apply a 2-3″ layer of organic compost if at all possible. This is optional but will help you grow a catch crop while the plastic is working. It will also create land ready for immediate planting.
On a calm day, lay heavy-duty black polythene plastic flat on the ground where you’d like to kill off weeds and vegetation. If you need to use multiple pieces, overlap them by at least six inches. When you’re happy with the positioning, weigh or peg the plastic down around the edges and in the middle. Wind can blow it up and away if it’s not secured, and I’ve seen it go whipping fifty feet in the sky before! If the area is large, pop fine holes in the plastic to allow air and moisture through. I wouldn’t do this for smaller areas that are less than four feet wide. It helps preserve soil moisture if you cover larger areas, though.
How Long to Leave the Plastic On For
Once the plastic is down, all you need to do is leave it to do its work. Heavy-duty plastic kills weeds and other plants underneath by excluding light, excluding at least some water, reducing vertical space for plants to grow, and cooking the soil underneath in the hottest months. The time it takes for this to work is different based on the time of year, the types of garden weeds you’re trying to kill off, and the temperature.
Annual weeds and grass die off relatively quickly, but tougher weeds need more time. As a general rule, leave the black plastic on for two to three months in summer. During that time, the sun’s radiant energy will cook the plants underneath, raising soil temperatures and potentially killing weed seeds on the surface.
If the weather is mild, wet, or cold, leave the plastic on for six to twelve months. That’s because if plants are dormant or the sun isn’t as hot, then the plastic needs more time to work. You’ll probably also need to leave the plastic on for this long if you’re dealing with stubborn and persistent weeds like many perennials are. They hang on almost admirably but eventually will succumb to the hostile environment under the sheeting.
Grow Crops Through the Plastic
While you can cover the land with black plastic and leave it, you can also get a crop while it’s doing its work. This is a common tactic for new no-dig beds, and you can make X-shaped slits in the plastic and plant resilient annual crops like pumpkins, squash, and potatoes through. There may be some weed growth through the slits, but the big leaves of squash and potatoes can help stifle them by blocking sunlight.
Because there will be quite a lot of pests under the plastic, choose types that won’t be as affected by slugs or cutworms. Just make sure that you put a good layer of compost on top of the land before setting the plastic over it. Without compost, any crops you grow in the area will likely be unhappy and unproductive. Crops can also help disguise the look of plastic sheeting in your garden.
What to do After Lifting the Plastic
Though there are cases when commercial farms use black plastic long-term, the goal in a typical garden is to remove it as soon as possible. However, the time it takes for your land to be cleared by black plastic is going to be different every time. Just have a peek every now and again by lifting up the edge. You can lift the plastic and proceed to the next steps when you can see that the land underneath is bare or the plants are all dead. If you’re only planning on using part of the land to grow on initially, peel back just that section. Leave the plastic on the rest until you’re ready to work it.
Take the time now to remove pests like slugs and dig up perennial weeds. Any perennial weeds that are left will look white and spindly since they’ve not seen light in a while. It makes them easy to spot and dig up. You might also spot dead plants on the soil surface – desiccated or slimy plant material. If you’re sure it’s dead, you can leave it there.
If you cover a large area with plastic sheeting, you may also have very dry soil once you lift it. This can happen, but usually, only the top layers of soil are dry. It will recover once it’s been wetted by rain and flooded with nutrients from compost. It may seem dead, but life is there, just waiting to make a comeback.
After removing the last living weeds, the land is ready to work with. For a no-dig bed, spread a thick (3-6″) layer of compost on the ground and plant seedlings directly into it. Even though you’ve not dug the soil underneath, the plant roots and worms will cultivate it for you. The thick layer of compost also suppresses weed seed germination by excluding light.
Cons of Using Black Plastic to Kill Weeds
Using black plastic to kill weeds is, in my opinion, an easy and organic way to clear land. You can save on physical exertion, avoid using chemical agents, and wait for the power of solar energy and time to do the work for you. In the end, the plastic can also be folded up and used in the same manner many times over. It could also be used for other things if it’s not perforated. For example, you could use it to line a garden pond or cover outdoor furniture in winter. We also reuse black plastic when we get deliveries of compost or wood chips. It protects the surface underneath and makes cleaning up a breeze.
The only real downside that I can think of is that it isn’t the most attractive. You could disguise the plasticky surface with wood chips, bark, or gravel if you wanted, though. If you want a more permanent weed barrier, don’t use plastic. Use durable landscaping fabric instead since it allows moisture through and isn’t slippery. I nearly broke a bone slipping on black plastic covered in wood chips before! It could also be a hazard if you’re walking on it with snow cover on top.
Sometimes, plastic sheeting can dry the soil out, as I’ve already mentioned. I’ve only ever found this to be the case when very large sheets of plastic were used, though. There is some criticism of the method because of it, but dry soil is only a temporary repercussion of clearing land using black plastic. Soil life, such as worms and microorganisms, retreats to where the soil is moist and more hospitable. Once the plastic is removed and the soil becomes moist again, they’ll move back, though.
From Weedy Land to Productive Garden
Over the years, I’ve used black plastic to kill weeds perhaps dozens of times now. I’ve covered large areas to create a brand-new allotment garden from scratch and small 4×6′ vegetable beds for temporary weed control to warm the soil early in spring. I’ve even covered two long and steep banks at my home with black plastic to clear it for wildflower borders. The method is easy, and it works, so it’s one that I’ll always return to to clear land in the future.
How to kill weeds with black plastic
- Large stones, weights, or pegs
- Garden fork
- 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.