Qualified praise for biodegradable plastic mulch

Tomato transplants waiting in the cold frame. Credit Kathryn Simmons

Tomato transplants waiting in the cold frame.
Credit Kathryn Simmons

We’re having a very busy time in the garden. Because of late cold weather followed by too much rain at once, all our transplanting has been delayed. We’re up-to-date in the permanent raised beds – we’ve planted out lots of lettuce, senposai, early cabbage, scallions, our first cucumbers and summer squash, and chard, tomatoes, eggplant, celery and okra. We’re also up-to-date on raised bed sowings of carrots, turnips, beets, snap peas, snow peas, bush beans, edamame and asparagus beans. But in the row-crop areas, it’s a different story. We have planted out our main-crop cabbage and broccoli, our “spring” potatoes and sown our first corn. We’re about a week behind on our big transplantings of Roma paste tomatoes, peppers, melons, sweet potatoes, and therefore watermelons. It’s also time to sow more beans, cucumbers and squash. But we’re getting to it as fast as we can!

We’ve added in late afternoon transplanting shifts, and some random evening weeding (which has helped us get the first round of carrot and beet thinning done). Yesterday I measured and flagged the areas for Roma tomatoes, peppers, melons, beans, edamame, watermelon, and sweet potatoes. I set out the mainline tubing for the drip irrigation and dropped the shuttles of drip-tape at the ends of the patch. I wrote about our drip tape shuttles a while back. They are part of our commitment to minimize our agricultural plastic usage by making our plastic stuff last. The shuttles let us fairly easily reuse the drip tape.

Re-using drip tape, unreeling it using our shuttle and garden cart system. Photo credit Luke Stovall

Re-using drip tape, unreeling it using our shuttle and garden cart system.
Photo credit Luke Stovall

After running out the drip tape, flushing the lines, capping them off and testing (and fixing!) any leaks, next we’ll roll out biodegradable plastic mulch. This wonderful product has changed our lives! And yet we are not all firmly convinced it is an ecological choice. The language in the accessible information can be confusing.

We like using biodegradable plastic because it warms the soil, leading to much earlier crops, it keeps the weeds down for a few months, and then it falls apart, so we don’t have to remove it and add to the heaps of agricultural plastic trash. It’s especially good for vining crops like watermelons and sweet potatoes, because by the time the mulch disintegrates, the vines cover the ground and weeds have little chance. Why we qualify our praise is because it has been hard to find out what it’s made of, and what it disintegrates into. And for some, there’s that knee-jerk reaction to anything plastic!

Biodegradable is not the same as bioplastic, nor as bio-based. Bioplastics are a type of plastic made from biological substances rather than from petroleum products alone. Some are biodegradable, some are not. Wikipedia distinguishes two types of bioplastics 1. Oxo-biodegradable plastics (made partly from natural sources, with non-biological additives) – they break down into biodegradable materials;  and 2. Plastics made wholly or in part from vegetable material. The second type are often made of cornstarch or sugarcane, but could be made from other agricultural crops. Some biodegrade, others don’t (eg those made from sugarcane ethanol). I found the Wikipedia explanations confusing and some read as if they were funded by petrodollars: “It is difficult to see why . . . resources . . . should be used to produce them when the raw material for conventional plastics is so inexpensive and is available in unlimited quantities.” Really.

I found a European Factsheet on bioplastics which clears some of the confusion. There are conventional (petroleum-based) plastics and there are bioplastics. Bioplastics may be divided into three categories. The first is the bioplastics which are not biodegradable. The other two are biodegradable, and differ in whether or not they contain fossil-based materials or only bio-based materials. Our goal would be to get biodegradable bio-based materials.

The two most commonly available biodegradable plastic mulches in the US are Eco-One and Bio360  from Canada. Novamont, an Italian company, imports Biotelo, the original mulch film made from their product Mater-Bi.

Eco-One describes itself as Oxo-degradable. It claims “Environmentally sound degradation: Laboratory studies indicate that this degradable plastic breaks down into CO2, H2O and biomass without toxic residues. Degrades fully both above and below the soil.” It’s available clear (for encouraging early emergence of sweet corn) and black, including an extended lifespan version for those wanting a 5-6 month window before it degrades, rather than the usual 3-4 months.

Bio360 is made by Dubois. It’s entirely biodegradable, and made from Mater-Bi, a non-genetically-modified starch with vegetable oil resin. Mater-Bi® is a wide family of fully biodegradable bioplastics, sold in pellet form to the industry of bioplastic converters. Mater-Bi®’s ingredients consist of plant starches, “mainly corn starch, with fully biodegradable aliphatic-aromatic polymers from both renewable raw materials (mainly vegetable oils) and fossil raw materials. Mater-Bi breaks down into carbon dioxide and water, with no mulch residues in the soil.” (see also the Cornell University 2006, Biodegradable Mulch Product Testing). Ah! So even Mater-Bi contains some fossil raw materials. And of course, fossil fuels are used in the manufacturing process. Life is so full of trade-offs!

I found explanation of the chemistry from the Biodegradable Products Institute, as part of a 2012 petition to the USDA National Organic Standards Board to allow “Biodegradable Mulch Film Made From Bioplastics”.  The bioplastics they were petitioning for are not polyethylene like regular plastic mulch, but “polyesters, polymers formed by the reaction of a hydroxyl group and a carboxyl group. The natural world is full of ester linkages. Living cells and organisms have developed enzymes to hydrolyze the ester linkage. Examples of natural esters are fats and oils, where three fatty acid molecules are esterified to glycerol/glycerin; natural waxes, where long-chain alcohols are esterified to a fatty acid; and some natural flavors, such as banana flavor, n-amyl acetate, an ester of n-amyl alcohol and acetic acid.” Biodegradable bioplastic mulch film materials can contain carbon black to make the film black to absorb heat from the sun. Or titanium dioxide to create  white mulch, which can cool surface soil temperatures slightly, by reflecting most of the sun’s heat.

NatureWorks‟ PLA INGEO, Ecoflex® F Blend C1200, Ecovio® F Film and Ecovio® F Blend, Mirel™, were also listed in the petition as suitable Biodegradable Mulch Films made from bioplastics. In contrast, oxo-biodegradable materials were not included in their petition, because they did not fulfill the two criteria proposed to address the concept of “fully biodegradable plastics”.

The Organic Standards are inconsistent, as §205.206(c)(1) permits “mulching with fully biodegradable materials” but §205.206(c)(6) requires that “plastic or other synthetic mulches . . . are removed from the field at the end of the growing or harvest season.”

I’ve been buying from Nolt’s Produce Supplies in Leola, PA (717) 656-9764. They sell Bio360 BTB645 4′ x 5000′ for $345 plus shipping, and Eco-One E1B548 4′ x 8000′ for $243 plus shipping. They are a company that doesn’t use email or websites, and they’re closed on major Christian holidays, so don’t call then! Johnny’s sells 32′ lengths for $17.95. Robert Marvel sells whole rolls of Eco-One and Bio360 (call for prices).

The first biodegradable plastic we used was Bio-Telo, (Mater-Bi). Since then we have sometimes bought that and sometimes Eco-One. I had not appreciated the difference. Knowing what I know now, I’ll buy the Mater-Bi types in future, rather than the oxo-biodegradable ones.

Next time I’ll write about how we set out biodegradable mulches without he use of any machines. Sorry for the delay in posting. I’m working on making improvements to my website, honest!

8 thoughts on “Qualified praise for biodegradable plastic mulch

  1. I am new to organic gardening and gardening as well. I recently saw your article on biodegradable mulch. I have raised gardens and was wondering about what time of year that this should be put onto your soil. Also, is the plastic covered with soil and how and when do you plant the seeds. Are the seeds planted under the plastic??? I live in Oklahoma and it is the end of January right now. I would appreciate any insight into this gardening technique.

    • Lisa, the biodegradable mulch should be rolled over the well-prepared soil immediately before you plant. If rolled ahead of time, it will start to biodegrade before you plant, and its life will be shorter, perhaps shorter than the life of your crop. Whenever you want to plant a crop that appreciates warm soil, that’s the time to use it. Don’t sow the seeds and then cover the whole bed with plastic – the seedlings will die. After all, that’s what you want to happen to the weed seedlings! Poke holes through the plastic for each seed. For transplants, just poke a hole with a trowel where you want to pop in each plant. Good luck!

        • For use on a certified organic farm, I use the plastic biodegradable mulch in the spring to cover raised beds before I plant. I allow the weed seeds to germinate under the plastic and die. I then remove the plastic before I plant my crop. It I impossible to remove after the crop is finished. It creates a stale seed bed substantially reducing thevamount of weeding I have to do after the gardens are planted.

          • I don’t know where you are located. I had thought that biodegradable plastic was not yet approved for any use on Organic farms in the US (even if removed later). The biodegradable plastic deteriorates fairly quickly – I imagine it being difficult to remove after even a short time on the ground. How long can you leave it before removing? Have you tried using either reusable landscape fabric or reusable black poly tarps (like silage covers) to kill weeds this way before planting? I’d love to know hoe they compare.

      • What kind of irrigation do you recommend if I use the “square foot” type raised garden and using the biodegradable plastic mulch that we talked about earlier?

  2. Lisa,
    I can’t really picture your garden from your description. If the beds are surrounded by wood or block walls, I think an overhead sprinkler would work best. Generally drip tape is used with plastic mulches. While the plastic is in good condition, not much water from overhead reaches the roots (whether rain or overhead sprinklers). But drip tape is hard to use with raised beds, because the tape needs to lie flat to work (it gets pinched closed if it goes over edges). How big is your garden? Could you handwater with a hose and a sprayer wand? If it’s too big for that, then either buy special adapters to use drip tape in boxed raised beds, or use a sprinkler, although it will be inefficient and most of the water will run off the plastic. I can’t think of a good solution. Sorry. Pam

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