Warning, the following is full of anecdotes and opinions, not science.
I often get asked if plastic mulch is ok for soil. Now, I understand the allure of plastic mulch, I really do. It’s cheap, it’s impermeable, and frankly, it works for stopping weeds when you have a large patch of bare earth. And yes, I have used it. I do still use it. But I have my reservations, which I will go into a little later.
People talk about various chemicals leeching into the ground. That may or may not be true, you’ll need to do your own research on that. People talk about the environmental damage plastic causes. It certainly does cause a lot of damage, both in it’s production and at the end of its ‘productive’ life cycle and beyond. But I feel the biggest problem is actually black plastic mulch is too good at what it does.
The allotment I took on this year was half covered in black plastic mulch which had probably been there over six months, possibly more. To be honest, at first, I was pleased! As the other half of the allotment was covered in weeds and grass. It took me several weeks to dig over that part. When I got to the plastic mulch I was happy.
Is black plastic mulch good for soil? Well, I lifted it up, and it was then I noticed how ‘flat’, and dry the the soil looked. But hey, there were no weeds! Whilst giving it a quick fork over I didn’t notice many worms. In fact, this soil, in wet old blighty, looked arid, thin and lifeless.
So I planted my seeds in the formerly plastic mulch covered part at the beginning of the season, and waited. And waited. And waited. Nothing. After a couple of months I saw some very limited and sporadic germination. But now at the end of the season, frankly, that end of the allotment has been bare most of the year. Nothing wants to be there… even the weeds (which took a while to come through) were less vigorous. I wasn’t growing anything particularly difficult, some carrots, beetroot, lettuce, garlic, onions, and radish. Yeap, you read that right, I couldn’t grow radish, possibly one of easiest things to grow ever. Actually, that’s not true, two radish managed to germinate the whole season.
Of course it may be that plastic mulch is not bad for soil and that there could be many reasons for my results. Duff batches of seeds, pests and so on. Seeds went out at the end of May so I doubt it was too early. I tried many other sowings to no avail. Let me tell you what that part of my plot yielded – about 5 super tiny carrots (1cm long), a handful of baby spring onions that never grew up, about 5 super stunted beetroot, one lettuce and 2 radish. One of the radish was massive, but only because I forgot I had planted it and went to seed.
So is plastic mulch good for soil? Well my opinion (and it’s just an opinion based on limited experience) is 80% no, black plastic mulch is not good for soil. I suspect the plastic mulch was too effective in stopping EVERYTHING. Worms, micro organisms, fungus, bacteria, all those things soil and plants need. There are probably some circumstances effecting this aspect of your soil is a worth while compromise, hence why I’ve not completely ruled out using black plastic for weed suppression. But I generally use organic matter for mulches (hay, grass, nettles, leafmould, rotted woodchips).
We took on another plot which was epically overgrown and I had planned on using black plastic mulch on that over the winter, but after my experience, I won’t bother. I may potentially look at ‘breathable weed control fabric’, but that gets rather pricey. So for now I will stick to bio mulch, ground covering green manures, hoeing and cardboard when necessary.
At my allotment (community garden), many plot holders are covering their bare plots over at this time of year. In fact, some of the plots are almost completely covered, which seems a waste. Aesthetically I don’t find plastic mulch pleasing, but I’m a practicality first kind of person. But I wonder if it will effect their plots like I think it effected mine.