The Case of the Unapproved Biodegradable Plastic Mulch 10

I wrote this article for ACORN’s summer 2015 newsletter and am now republishing it here.

biodegradable mulch

At the end of March of this year (2015), we found a memo in our inbox from Ecocert (the organic certifying body that we are certified with). In this memo, we were told that we would no longer be able to use the biodegradable plastic mulch (made with non-GMO corn starch) that we had been using unless we removed it after use. We were surprised and concerned. It was definitely a little last-minute! We still had leftover rolls of it at the farm from last season and had made our order for this season back in December (when we do a lot of our inputs purchases). And the removal part….it’s pretty tough to completely remove something that biodegrades as it’s in use.


Bryan and I have been using biodegradable plastic mulch (which I will refer to from now on as biofilm to reduce typing) since the first year we started Broadfork Farm. As small farm operators, we have appreciated the reduction in our time spent weeding in particular. But there are other benefits to using plastic mulch, like warming the soil and retention of moisture in the soil. With our deep feelings of stewardship for the soil, we have also liked how we have been able to keep more of the soil covered during the season (with the biodegradable mulch in the beds, our pathways have been maintained in living mulch that we mow). Soil left bare tends to create its own “cover” of a dry, dead, erodible soil layer.

clear plastic mulch

We knew that, as a manufactured product, biofilm wasn’t the perfect solution in our utopian organic vision. But it was a solution we preferred to regular plastic mulch (with the required pulling up at the end of the season and taking to the landfill) or frequent cultivation.  There are of course other mulches like straw or leaf mulch but they didn’t fit in as well with our whole system (but rather have fit in with some crops in certain instances when we could access sufficient quantities without prohibited substances).

We had often talked about the fact that we didn’t think we could have made 100% of our household income from our farm from our first year without the use of biofilm. We even listed it as one of our 5 favourite market gardening tools! Especially in our first year while we converted hay fields to vegetable fields…while growing vegetables. The sod clumps that we’d overturned were too lumpy to be able to use a wheel hoe (or any other kind of hoe for that matter) for weeding.

lettuce on plastic

So, after receiving the Ecocert memo, I contacted other people involved with the Organic Standards and asked, what’s up with this? It turned out, that our Canadian Organic Standards had never allowed the use of the biofilms (without removing from the field after use) that are currently available in the marketplace. But there was a lot of confusion around this, both by farmers and certifiers. I think the confusion stemmed from the language of the Standard (very Standard-y) and the uncertainty of exactly what substances each biofilm on the market contains.

This is what the Standards said:

Fully biodegradable films: permitted without removal if they do not contain substances prohibited by par. 1.4.1 of CAN/CGSB-32.310, Organic Production Systems — General Principles and Management Standards.

I think it was clear to everyone that the biofilms couldn’t contain GMOs or pesticides. And the ones organic farmers were using don’t contain these.

Many organic farmers had happily been using this input for years and so, when the memo came out right at the beginning of the growing season, it was a big shock. People involved with the Crops Permitted Substances List (PSL) working group of the Organic Standards Technical Committee, the Standards Interpretation Committee (SIC), and the Canada Organic Office (COO) at the CFIA all started trying to figure out an appropriate and fair solution.

So, why aren’t biofilms allowed? Well, all of the biofilms on the market currently contain a certain percentage of petroleum source materials (which are prohibited) that seem to be referred to as raw fossil-based ingredients (by manufacturers). The biofilm that we had been using, while having the lowest percentage of petroleum source materials of any other biofilm, is still around 20%. I didn’t like learning that. And I was disappointed it wasn’t clearly expressed by the companies that were manufacturing and selling these biofilms. I had thought the biofilm we were using was actually 100% non-gmo corn starch.

Then there is the issue of biodegradability. Most farmers who have used these biofilms know that the biodegradability varies (so the ‘fully biodegradable’ part of the above Standard was a tricky one). It varies from farm to farm, field to field, season to season. In particular, it varies based on the life in the soil, the soil temperatures, and the soil moisture. There has been a bit of research done on this but not enough. The primary ingredient in the biofilm we’ve used, the corn-starch material Mater-Bi, is shown to be compostable in ideal composting situations but that’s not the same as using it on top of the soil in highly variable field conditions.

kohlrabi on black plastic

As I was trying to learn as much as possible about this input, I realized that there are currently too many unanswered questions. Like what happens to all the bits (even the bits we can’t see with the naked eye) that don’t fully biodegrade? Are they contributing to those floating garbage islands in the ocean? Are they being taken up into the web of life through food chains (insects, birds, mammals) and their materials concentrated? And to what effect? Are the microorganisms in the soil changing…adjusting to a new food source….and if so, is this harmless or harmful on the balance of life in the soil? Are there residue buildup issues we should be concerned with (the labelling always says “No toxic residues’ but what is this claim based on? Over how many years and with how much biofilm use? Is this claim unlimited?)?

With both the sustainability of farm businesses and care of the soil in mind, the Organic Technical Committee brought forward a revision to the 2015 Canadian Organic Standards. This is that these biofilms with the prohibited substance of petroleum products (all that are currently on the market, remember) will no longer be allowed unless removed from the field….but that, in order for farmers to figure out new systems without the use of these products…or, fingers-crossed, time for the manufacturers to figure out a way to change their products to be compliant….organic farmers will still be allowed to use the biofilms as they have been (i.e. tilling back into the soil) until 2017. And, for this 2015 season, since the newly-revised 2015 Organic Standards won’t come out until the fall, the Canadian General Standards Board has sent out a bulletin saying that this new Standard will be in effect for this season  as well (you can read that bulletin here).

As organic farmers, we are committed to being stewards of the soil. While we need all the help we can get with improved products and efficient techniques in order to provide ourselves a livelihood, as small-scale organic farmers, we realize that we are only the caretakers of this land for the tiny time period of our lifetime. This land needs us to consider our impact on the generations that follow ours. So, we are always researching, learning, and questioning what we thought we knew.

Bryan and I have decided that, beyond using up our leftover biofilm from last year (we cancelled the order we had made back in December after the memo came out), we wouldn’t use any more biofilm (unless the manufacturers make some serious improvements in the future). But how will we replace it’s benefits in our operation?

At this point, we’re thinking about increasing our annual use of landscape fabric (which can be rolled up at the end of each season and re-used for many years). This reduces our opportunities for living mulch in our pathways which we’ve really liked having…though there are always plenty of beds that don’t get any mulch at all (like beds of salad mix, carrots, salad turnips, radishes) that will still have the living mulch pathways.

Landscape fabric

We’ve also been experimenting with rolling/crimping rye and flail mowing rye and then planting fall brassicas (like cauliflower, broccoli, kohlrabi) into it.

flail mowed rye

Since biofilms haven’t been allowed on U.S. organic farms (but many farmers there have wanted to), there has been some thought and a little research coming from there on this topic.  Here are a few resources you may find interesting for further reading:


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10 thoughts on “The Case of the Unapproved Biodegradable Plastic Mulch

  • Dan Brisebois

    Great post!

    We were dismayed this spring to hear about switching our biotelo practices. Your article fills in some of the blanks behind the situation.

    I’m not sure what we’ll be doing next year.

    We have been using some landscape fabric. But one challenge is that the fabric can be a disease vector on your farm. This scares us from completely committing to landscape fabric for crops like tomatoes.

    Later, Dan

  • Sandi

    Hi…I’m sorry about your predicament with the plastic mulch…an alternative, which you may already be familiar with, is WeedGuardPlus Standard Weight Organic Grower Rolls, which we’ve been using with either straw or soil on top…we’ve found it biodegrades within about 4 months so it’s a seasonal use…it’s OMRI-listed… there is also a heavy weight variety…

    • broadforkfarm Post author

      Thanks Sandi! The small-scale, organic ag extension officer in our province was attempting to do a trial of Weed Guard Plus on a few farms (including ours) this year. Unfortunately, our certifying body won’t accept it (it’s OMRI-approved but not approved for use in Canada….the company hasn’t been willing to gibe up their proprietary info). I’d love to try it out if I could!

  • Suzanne Townsend

    Perhaps the landscape cloth could be washed (hosed down) with some kind of treatment to clean it each year? I am so glad to hear that plastic will no longer be used.

    • broadforkfarm Post author

      Just to clarify…plastic will still be used (and probably more will be used to replace the biofilm), just biodegradable plastic mulch will not be used (by certified organic farmers….non-certified farmers are still free to use whatever they want).

    • broadforkfarm Post author

      We’re still happiest with a mixture of strategies. We’re definitely using more landscape fabric. We’re still working with rolling down (or mowing) overwintered rye and then planting into it. And we’ve been excited by doing compost mulching (though we’d like to get a spreader to help us with this).