Where there is a will there is a way

Thursday, September 13, 2012

How to prevent weeds without using plastic weedmat

Look at all the plastic waste I cleared from just one little section - plastic weedmat left behind by prior owners!

In New Zealand, if you don't prevent weeds in your garden (yard) they just might grow larger then you! With all the lovely sunlight pouring down, and rain, the biggest challenge when gardening is helping the right species flourish, as every species crowds in where it can. Unless...

Non-breathable plastic weedmat (straight plastic) is not a good choice for preventing weeds for this reason. As a weedmat it soon becomes uneffective anyways, as new soil forms over top of the weedmat as plant matter breaks down on top of it. What you end up with is a sandwich of soil, then a layer of plastic pollution, then more soil underneath (but compacted and straining for oxygen, with no earthworms).

A better choice is anything that breaks down, like jute weedmat, or they even have wool weedmat here in NZ. But these options are expensive. Some people suggest using a thick layer of newspaper - but in my experience it goes all over the place. We did try something called "Geocil", my husband bought it because it was affordable and does break down. But to a perfectionist (such as me) that's not perfect - although breathable it is made out of polypropylene and will cause some pollution to the soil as it breaks down. (The plastic separates into smaller pieces that you can now see are made up of many strands - until you grab them and dispose of the pieces bit by bit into the landfill anyways.  Not a great solution at all.  See photo below.)

From my feel for it, and seeing forests, and also suggested by horticulturalists - you can avoid using weedmat at all though by using ALOT OF MULCH. In a foresty garden, mulch is bark nuggets, or best ever - pieces of ponga log. In a veggie garden straw, or hay is great for nitrogen release. This represses weeds without choking off the air that the soil needs, and keeps the soil from drying out - making a lovely cool environment for worms to flourish.

Mulch is a great option for hot and dry climates too. My sister-in-law Iris is a great gardener who lives in near San Diego in Ramona, California, where the growing season is very hot and dry with less than 12 inches of rainfall per year (300 mm). She can't swear enough about the value of using mulch on her veggie garden for preserving moisture (and preventing weeds).

For more about weedmat and soil, check out this page: Greg's Indigenous Plants and Landscapes, a website about environmentally friendly landcapes by Michael Hough, Professor of Landscape Architecture, from York University, Canada. He really goes into depth about the subject.
Key points:
"Plastic weed mat was widely used to suppress weeds for revegetation projects during the 1970's and 1980's. However it use is now largely viewed as a disaster and has been replaced by biodegradable weed mat.
"Unfortunately the landscaping industry and the gardening public did not get the message. Woven plastic weed mat is still used widely by the industry and in worse case scenarios black builders plastic is used as a cheaper alternative.
"Plastic weed mat will cause many problems for your soil and your garden:
  1. It impedes or stops rainfall soaking into the soil.
  2. It prevents worms from mixing organic matter from the mulch through the top soil.
  3. It impedes or prevents aeration of the top soil.
  4. Its slippery surface causes the mulch to slide off exposing unsightly patches of bare plastic.
  1. Weeds still grow through cuts and holes in the plastic or on top of it and then you unavoidably tear large holes in it when you remove them."


Lisa said...

Love what you're saying about not adding plastic to soil and about mulch being the best approach but have found it hard where I live (Brisbane Australia) to get weed free straw or hay. Any suggestions?

Nonavee Dale said...

Yes I do, Lisa! Pea straw is great, the worst weeds are pea plants that come from it. Dead leaves, bark mulch is the main one for foresty areas. I am accustomed to NZ, but do know that the drier the climate the more important mulch is to preserve moisture for the plants. They need to be watered less then, and also there is protection for bacteria and worms to thrive and do their work.

If you want a weed MAT then coconut fibre (koir) is the best weedmat you can get. It does cost though - so a cheaper alternative is lots of newspaper then mulch overtop.

My sister-in-law in San Diego (total desert climate) found using uber heavy mulch she had to water her corn so much less...

Unknown said...

I live in the bottom of the south isalnd in nz where lack of moisture is not an issue. I am on a farm and trying to fill in alot of unutilized ground with plants rather than spraying weed killer what would uou suggest I could use as a weed mat? than land does jot beling to me and the land owner will not come to the party in regards to buying anything ( have funded this project myself) what is something cost effective for a large group of areas. thanks Sandy

Nonavee Dale said...

Anything like straw. Even pine needles. Anything you can bulk up like leaves or tree chips. Seaweed.

Just think of how nature does it in a forest - old rotting ponga logs, bits of paper, anything piled up will deter weeds and break down slowly, feeding the soil without cutting it off from oxygen.