It seems oh so tempting doesn’t it? They sell nice long, sturdy rolls of it at the building center and you cover it up anyway. Why not just use vapor barrier (or another plastic) as your weed barrier? This year and last I spent and extraordinary amount of time taking out plastic weed barrier and replacing it with a proper and long lasting barrier instead at two huge properties.
Why you might think it’s okay
On the surface it might seem that plastic produced for another purpose is a great solution for your gardens but it almost never is. You might think that:
- It’s super cheap and lasts forever
- nothing will ever grow through
- you cover it up anyway
- It does make the mulch last longer
It’s not a good idea though and the main reason is it doesn’t allow water to penetrate. There are other reasons and we will get into those too but even with big holes cut for shrubs the plastic just doesn’t let enough moisture through to keep any sort of garden going. The first property I removed plastic from was two summers ago. The customer has several large gardens through her sprawling 2 acer plus property. Several had just failed to thrive for lack of a better term. It seemed everything she put in there just didn’t really grow and was dead a few years later. At one point she said she had gone through and punched fist sized holes in the plastic throughout but it didn’t seem to have helped. She thought and I agreed that it probably was a water thing.
That summer was very dry and the work took me many days and evenings to complete. As I pulled back the plastic and replaced it with permanent (and water permeable) barrier the ground underneath was so dry it was cracked. The summer was very dry but the soil hadn’t actually cracked at anyone else’s home. One morning I showed up to do a large section after a welcomed night of heavy rain and I could see just how much water had made it through all those fist sized holes. The answer not very much at all. The wet ring really didn’t extend out beyond the border of the hole at all and the soil wasn’t wet beyond an inch down. That despite the lawn was actually marshy in spots when I arrived. In that moment I knew it was in fact a water thing for sure! It’s been a little over a year since I took the plastic out of that property and wouldn’t you know it the shrubs that were so clearly suffering have visibly grown and are covered in new growth.
I spent a lot of time doing the same thing at another property this last spring. Besides not allowing things to grow there are other issues with plastic in the garden too. If there is any wind it inevitably blows the mulch off the plastic and exposes the ends. Once this process starts it just gets worse and worse so that soon you have plastic fingers flowing from your garden in the wind. When it does rain the moisture is trapped on top of the plastic in the mulch which in wetter months of the year encourages a lot of mould growth in the mulch. Not only does that not look great it can smell pretty bad too.
Sometimes, very, very rarely a little bit of plastic can go along way. The key there is just a little bit. This summer I took out three large stands of multiflora rose and one property. This white rose is generally considered to be an invasive species in North America. And when I say large I mean each stand filled the long box over the cab when strapped down hauling it away. Since this species likes to rise up for literally the next 25 years I did cover the origin of the problem plants in plastic and a more attractive barrier. Each cover was about 4 square feet. In cases where you are cutting out and getting rid of something invasive a small amount of plastic under your barrier can be a good idea. Use as little as you can and know that you will not be able to plant there for a very, very long time. If you have an area where you want literally nothing to grow then and only then is plastic a good choice. When I do very occasionally use plastic I like to use roofing underlayment made by one specific company because it’s black. If it does poke through it will just blend in with the mulch.
If you’re tempted to solve your gardening problems with plastic, just don’t. It might be time to call in for some help instead!
AMK Landscaping 
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