Eco Weed Suppressant

Managing weeds is a massive issue for us, particularly as we expand but are not at a point where we can afford people power to help on the field. Plastic weed suppressant fabric is commonly in used in horticulture but the idea of covering our beautiful field in black plastic feels uncomfortable. No dig techniques whereby you kill off the grass and weeds with a mulch of cardboard covered in compost necessitate transporting massive quantities of manufactured compost even for small scale growers. Neither seem particularly ‘eco’ but spraying weed killer doesn’t fit either. So as part of our Eco-Innovation Cumbria project we asked our intern, Dr Laura Giles, to look at weed suppressants and which had the lower GHG emissions.

Our research, which is based on very limited data, compared Mypex, woven polypropylene (non-recyclable plastic) weed suppressant fabric, with Strulch, a commercially sold straw based mulch, and locally produced compost from garden waste.

Calculations based on (very limited) data about production and transportation, show that by virtue of being used for 10 years Mypex generates the least GHG emissions.

When Mypex and compost are used optimally Mypex contributes 0.0317 kh Co2 per m2 and compost mulch 1.934 per m2, a significant difference. Strulch, if composted (based on limited data) is between 0.06 and 1.03kg Co2 per m2. If you grow on an acre and convert half into flower beds, using rows of bed with paths in between, that equates to 64.12kg co2 for mypex or 3913.31kg c02 a year for compost.

Is it eco?

So does this mean that Mypex is eco?! Or does it mean that it’s the least bad? Does this mean that growing using this oil based product is sustainable?

One of the advantages of mulch is that it helps develop healthy soil, providing nutrients, building up good microbes and improving the texture. Arguably mypex still requires soil amendments, which if you’re using waste compost mulch increases your carbon footprint more than just using the compost mulch. And it requires more watering. We didn’t consider the growing implications of each technique in this study, just the GHG emissions, and so we haven’t taken into consideration the increased irrigation requirements from growing in mypex versus the reduced watering requirements of mulch. We also didn’t compare it with mowing grass or putting down wood chippings for paths, so it may be cost-cutting and labour saving to use it in that context but there’s no comparable evidence here. I think that further research to unpick these issues would perhaps be helpful.

So how are we using this research?

We are going to use a limited amount of mypex in our foliage field, in order to help the trees and shrubs establish. We will continue to pay somebody to strim and mow our flower field, and we will try to minimise weeds with cardboard (recycled) and mulch with muck from our farming neighbours (<1 mile), which reduces their methane producing muck pile and puts it to a positive use, while we build our own composting facilities.

If used strategically Mypex has the lowest carbon-footprint, which surprised me. Most surprising though is the very high carbon footprint of household waste compost, definitely raising the question about how sustainable that is as a technique. If this research does anything I hope it makes us all consider what we do and why we do it, and challenge the assumptions we make about ‘what is best’ and ‘what is sustainable’.