Episode 323. Weeds!!! ~ From Work to Ecology

Decarbonise the air, recarbonise the soil!

There were a couple of posts this week on the gentle topic of weeds. 

And they got me to thinking about my own journey to my current understanding of the little buggers and how they don’t bother me anymore.

My first ever garden as a child was a small one metre square attempt at growing wheat from my Irish neighbour’s chook feed.

Without knowing it, this was the first time I would re-enact the Neolithic. Making stone tools at uni many years later as part of my degree in archaeology, was another but that’s an entirely different podcast episode.

With the wheat garden I barely got my seed back.

Grain growing was when I and the Neolithic bumped up against weeds. Those first farmers and I created a space for food and the weeds dropped by. I assumed the weed seeds were just there even though there was no evidence of these weeds in the grass that had been growing there before my wheat experiment. I followed the usual path and hand pulled weeds for years, without thought. It was what had to be done.

It is still considered the only way by many. I recently observed, for three months, the workings of a certified organic farm. Beef, dairy, pigs and horticulture. The livestock seemed to be managed in a rational way. Rotational grazing, if not regenerative grazing but rotational nonetheless and the animals all glowed with health. The horticultural aspect was another story altogether and fits in with our theme of the episode: weeds.

This is what I observed: Black plastic sheeting across the ground for two weeks. Presumably to kill off any growing weeds by denying them sunlight. The heat generated by the sun on the black plastic would then solarise them and any seeds near the surface. Then the garden bed, 80 odd metres by 1 and a half, was turned with a mouldboard plough. Compost was added as top dressing and the bed left for two days then rotavated then shaped into furrows for Jerusalem artichokes and/or potatoes or into flat beds for seedlings with a soil shaper. So the soil was worked three times. For some crops, another layer of black plastic was laid on the soil and planted through, for the tubers and some seedlings, it was left uncovered.

The tubers grew up through the soil and the soil surface was covered, almost entirely with, in inverted commas, “weeds” as were the seedling beds not covered with plastic. Hours were then spent removing the weeds and leaving the soil bare. 

We’ll leave aside the CO2 released with each turning of the soil. The black plastic and the solarisation of the upper levels of the soil means death for any soil biota in that region, including, I assume, weed seeds. Turning the soil to place this solarised soil under simply brought any deeper seeds to the surface. A cycle of continuing efforts and frustrations.

Remember, all this is on a certified organic farm. So the techniques, the plastic, the ploughing and the weeding are all part of a system that grants a status that the farm is doing the right thing for the planet. It took me a couple of days to work out what was going on from a philosophical standpoint. This was the John Seymour way of organic farming with horses replaced with diesel and there was a lot of diesel used. Again this farm had been certified for a decades and was therefore under a certification worked out long before the CO2 impacts of farming, even this sort of farming were understood. The point is that organic doesn’t mean Natural, it means lack of chemicals and that’s not always the same thing.

There are other ways. Back to my personal journey which I hope helps others. 

Somewhere in my reading, Fukuoka or Mollison, I came across the concept of ecology. To be fair, we had covered biological succession in early high school science and that combined with an agricultural ecology started to make sense. Indeed, those two ideas and the deeper understanding of evolution that studying archaeology had instilled, brought me to a different view of weeds.

The standard definition is: A weed is just a plant in the wrong place. Wrong place for whom? Clearly not for the weed. So why is the weed there? What is its function, not from a farmer’s viewpoint but from Nature’s?

There were two “weeds” I’ve had trouble with: blackberry and scotch thistle.

Blackberry had overrun an orchard I took over. Blackberry is a problem across most of Eastern Australia below the tropics. In the tropics you can substitute the word lantana for blackberry and the same story will hold true.

What does the blackberry plant do in the ecosystem of a paddock? It grows rapidly, spreads across land like wildfire and, if we look closely, holds the soil still. It forms a matrix of support. Beneath the soil it stores nutrients in thickened roots. Saving them from being washed away in rainfall events. I was coming to the realisation that blackberries were a natural defense against overgrazing. Where the ground cover was insufficient to hold the soil, blackberries appeared as if by magic and mostly keep stock off the overgrazed soil. Given the predominantly shallow soils of Australia this is something that occurs quite regularly. 

What to do? The chemical approach is to spray with glyphosate. This has the effect of killing some percentage of the blackberry but does not repair the underlying problem of insufficient soil coverage. Therefore the conditions for the return of the blackberries are sown in their chemical destruction. A nice little earner if you sell glyphosate. The plants will also re-sprout from the roots as they have a nutrient store down there for just such an emergency. 

I wasn’t keen to douse anything in glyphosate but what to do? I saw the problem thusly: blackberry arose where there was insufficient ground cover, either living or, I hoped, as mulch. Blackberry would regrow at every opportunity until its root reserves were depleted. Could regular, say, once a week, slashing of the above ground part of the plant create a mulch to cover the soil and deplete the underground stores? As it turned out, yes. In one summer, one long hot summer behind a domestic lawn mower and secateurs, I cleared three quarters of an acre of blackberry and restored a thick sward below the orchard. Results may vary by location but the point I’m making is this: to remove a weed species requires an understanding of the ecology of the weed, its place in the ecosystem and an understanding of its life cycle. Combining these to remove the ecological niche in which the weed can flourish means the weed is gone for good.

Now to scotch thistle: When I moved onto a five acre block at the start of a winter, I noticed somewhat overgrazed paddocks. That Spring, thistles erupted out of the ground. I chipped them like a mad man. They grew back and flowered at ground level. Hmmm….

The next Spring the soil was better covered but the thistles took off. Chipping didn’t work. Back to the ecological thoughts. What do thistles do? They sent down deep tap roots to draw nutrients from the subsoil. The form rosettes and cover the ground to protect it. The next step was to observe the life cycle of the thistle. One year’s seeding equals seven years weeding as the old saying goes. 

I decided to pull out the trusty old domestic lawn mower but, and this was critical, only once the first signs of purple appeared on the seed heads. The reasoning was this: the plant would not produce new seed heads once the first ones moved into seed maturation and cutting before the seeds matured meant they wouldn’t be viable.

So I waited, telling the sceptical neighbours I had a plan. They didn’t seem convinced.

I hit the thistles as soon as I saw the first purple in the seed heads. Some of them were seven foot high so I knew I had reasonable soil under them. Long story short. It worked and the thistles never returned. The sward thickened up, the sheep kept it lush as they rotated about and all was right in heaven and on Earth. Well on that little patch of the planet I was responsible for.

So what am I trying to say?

Weeds arise only when the ecological niche they fill is created by the hands of humans or Nature. Most of the weeds in the vegetable gardens on the organic farm mentioned above are pioneer plants. When the glaciers retreated at the end of the Pleistocene and we entered the Holocene some 10,000 ish years ago, bare ground was the gift of the retreating glaciers. Nature abhors bare soil so these pioneer plants come in on the wind or with birds or bats and their droppings. 

If we look at these species they have a few things in common. Usually they have a rosette at ground level, a deep tap root and huge numbers of quickly dispersing seeds. By turning the soil, year in and year out we continually prepare the conditions for these these species to proliferate. In the same way acacias burst forth after a bushfire to trap nutrients and grab nitrogen from the air, they are legumes, so the post glacial pioneer species “save” the soil from being washed away. 

The clue then is to plant into a situation where these conditions do not exist. There is a link to post from 2007 showing how no-till worked on a nine year trial. It is doable on a broadacre scale. At the market garden level, what I’ve found works is mulch on raised beds. Not just any mulch but anything except plastic will work. Plastic has no place on our farm land. Food grade might have a place in the milking parlour or the dairy but never on the soil. Who knows or has even looked at what leaches out of the stuff into the food system?

The key to good mulch for me is to incorporate animal waste. That is manures and urine in straw or spoilt hay. The reason I favour this mulch over straight straw or compost even is food plants and animals evolved together long before we humans decided we could grow our own. By recombining the animal with the plant I more closely approach the natural systems I’m trying to emulate. In the same way Joel Salatin follows his herbivores, cattle, with his pastured poultry to mimic the birds picking over and distributing the manures of the bison herds, we need to constantly look to ways that mimic nature. For the good of our land, for the good of our crops and by a happy coincidence, to make our lives easier. Shovelling animal bedding onto a recently harvested vegetable garden bed is a whole easier than weeding a ground level beg by hand or even with a long handled tool.

It is the height of hubris to think in 10,000 years we could do better than 4 billion odd years of evolution, that is if we even think of biomimicry as a solution at all.

Look to the Natural world when you confront a problem. Ask yourself some questions. Is this thing, whatever it is, really a problem? Is nature putting in a stop gap measure to save my soils? What can I do to assist with the formation of niches that suit my crops and not the weeds? 

The solutions to most of our problems are right in front of us. We just have to take the time to see them and then implement them in ways that don’t make things worse.

And on that happy note I’ll draw this episode to a conclusion. 

Remember: Decarbonise the air, recarbonise the soil!

Thank you for listening and I’ll be back next week.



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