This past winter, we established large No-Till trial beds on a patch of weedy
and overgrown land next to the new polytunnel. Our aim was to test five different techniques for
creating growing spaces for vegetables, without tilling, digging or overturning the existing soil.
Part of the exploration was too see how these methods would be able to
prevent the existing vegetation from regrowing,
especially the perennial weeds that are fairly common in the area.
A few months later, it was obvious that this had failed, at least for
large sections of the growing space, and now I need figure out the best way to proceed.
When we set up the five no-till sections, I anticipated that there
would be differences in how early each section would be ready for spring sowing,
how well vegetable plants would grow during the first year and in subsequent years,
what pest problems we might have, and the long-term management requirements.
And that is the purpose of a trial like this, to determine how these 5 different
methods would compare for growing vegetables in the long run, but also how successful they
would be in the establishment phase with the suppression of the existing vegetation.
Like most other real world explorations, there are a lot of other variables, including varying
soil conditions, and uneven distribution of the different types of existing vegetation.
Although I expected some issues with perennial weeds, I followed the conventional advice for
each method, which generally involved placing a single layer of overlapping cardboard sheets
on the ground, with other materials on top. I deliberately avoided taking extra measures,
such as adding more cardboard layers, that could have reduced the risk of weeds regrowing,
partially because we had limited resources. As with many other things in this research
project I wanted to see how things might fail or succeed using fairly standard methods,
in order to better understand them. And that failure was worse than I expected.
Earlier in the spring it was obvious that the single layer of overlapping sheets of
cardboard was insufficient, as many weeds were growing up through the mulch and other material.
I realised that this was going to be a major issue.
I did a bit of work at the beginning of the season trying to knock back some of the growth,
but due to the busy spring and my absence from the gardens when it
was at a crucial time, I decided to let it go. Although there are still things that can be done,
it will be a challenge to grow any vegetables in these beds this year.
If I had acted earlier, the situation would have been better, particularly to
prevent the weeds from becoming even more established in the new growing material.
But, I also wanted to see how quickly and extensively the weeds would grow
back without any additional intervention, partially to see the differences between
the different methods, and to serve as a cautionary example.
The scutch grass was the biggest problem. This is a weed that I am very familiar with,
and have had to deal with it in many of the other gardens and growing spaces that
I have established over the years, and we usually spend the time to dig it out, often repeatedly.
But in a no-till situation this can be a really tough weed to get rid of because
of the long interconnected rhizome root system, which can regrow from any small
fragment of root left in the ground. In this no-till trial, the sharp tip
of leaf blades were able to pierce through the cardboard almost as if it wasn’t there.
It eventually regrew in all of the different methods, but it appeared earlier and more
extensively in the method that just had a thick layer of fertile soil on top of the cardboard.
This was possibly because this particular weed was more concentrated and stronger in that area, but
it also seems that the cardboard decomposed under the soil faster than under the other materials.
The extra weight combined with the available nitrogen in the fertile soil we added on top,
probably allowed slightly faster decomposition, as there is only a thin crumbling layer of
cardboard remaining less than 5 months later. The cardboard under the woodchip seems to have
lasted a bit longer, possibly due to the lack of available nitrogen, and the regrowth of the
scutch grass seems to have been delayed a bit, but the difference wasn’t enough to really matter.
Under the municipal compost, the layer of cardboard seems to have almost disappeared, and
it is hard to find this base layer under the hay or in the deep litter mulch of compost and straw.
So this cardboard might have lasted long enough to prevent the regrowth
some of the existing vegetation, but it definitely didn’t last long
enough to prevent the regrowth of scutch grass in any of the different sections.
Bind weed is also an issue,
with shoots of this vining plant finding their way between the layers of cardboard.
I think this can be a more problematic weed than scutch grass, as it has an
amazing ability to regrow from fragments of the root systems that can grow really deeply.
Thankfully it is less extensive in this area, but would be a bigger problem in the long run
if I allowed it to become established. There is also shoots of creeping thistle
breaking through the cardboard and mulch in quite a few locations, which is also a really
tough weed to get rid of, as it spreads through a deep horizontal root system.
Dandelion and dock have also regrown, especially the larger plants, that
were able to force their way up through the cardboard layer and material above.
There are not too many of these plants, and they can be dug out,
or we can place a large flat rock or paving slab on top of them until they die off.
Creeping buttercup and nettle plants are also present, but they can be easier to deal with
in this context, as they spread through runners along the surface of the soil,
but it might take a while to deplete the established root systems of the nettle plants.
We brought in another weed issue with the different material that we were using to
covered the ground, some of which contained annual weed seeds that have now sprouted in
the growing spaces, but these are much easier to deal with by hoeing or weeding by hand.
The overlapping layer of cardboard and mulch we used killed off some weeds,
slowed down the growth of other types of weeds and probably prevented some shoots
from emerging, but it was obviously not enough.
To rely on cardboard as a barrier, it needs to last longer than the reserves of energy
stored in the roots of the established weeds, and some of them have really extensive root systems.
Some people suggest using up to 4 layers of overlapping cardboard, but that is a
lot of cardboard for an area this big and we had trouble gathering enough for even just one layer.
More layers probably would have eliminated more weeds, and really slowed down the emergence of
others, but I suspect that even 4 layers would not have eliminated the established
patches of scutch grass. Once the cardboard gets wet,
and starts to decompose it becomes a lot easier for the sharp blades of the
scutch grass to pierce through this barrier. I think part of the issue is we covered the
ground at the beginning of our relatively mild winters, when most of the plants were dormant,
and the cardboard had already decomposed a bit when the weeds started to regrow.
Using the same material and methods when the weeds were actively growing in the
spring or summer probably would have been more effective, especially if it was not so wet.
And using a type of mulch over the cardboard that did not contain a lot of nitrogen would
probably delay the decomposition, and allow the cardboard barrier to last for even longer.
But working to maintain this barrier for long enough to kill off the weeds also
means that the roots of the vegetable plants that we want to grow would have
difficulty getting through this barrier and into the soil below.
There are probably ways around this, but the longer this barrier needs to last to kill
off the weeds, the longer we should probably delay growing a lot of types of vegetables.
Another approach would have been to weaken or eliminate the problematic
weeds before covering with the ground with cardboard and mulch.
Mowing the area regularly for at least a year would have seriously weakened or even killed off
plants such as bindweed and creeping thistle, as they can’t handle being cut so low so frequently.
Unfortunately the scutch grass can still thrive in these conditions.
Alternatively, we could have covered the entire area with a tarp for an extended
period during the growing season last year, to weaken the root systems of these weeds
before covering with cardboard and mulch. Part of the area had been covered in this
way for the entire growing season last year, to store the bales of hay and straw
that were eventually used, and the outline of where the tarp had been is visible in the
pattern of scutch grass that regrew. The tarp reduced the strength of the
weeds but it wasn’t in place long enough, or covered a wide enough area to eliminate them.
If I was to do it again I would want the entire area covered with a tarp or ground cover fabric
to weaken the plants for at least a year. The other option would have been to dig over
the full area first, removing as much of the mass of weed roots as we could.
And if we dug it over during the growing season last year, it would be better to leave it long
enough for the root sections and fragments that we missed to re-sprout so that we could dig them out
again before covering with cardboard and mulch. So unless I want to kill everything off with
herbicide, we either need to cover the whole area for a long time with light omitting with
light omitting fabric or tarp, spend the time and energy to dig over the full area
before covering, or use a lot more cardboard, and possibly a combination of a few of them.
When I first saw the scutch grass appear in a few sections I thought that I would
be able to cover the affected areas, and continue to grow in the rest of the trial
beds for the season, dealing with any other isolated weeds as they appeared.
But as the spring progressed it was obvious that scutch grass was appearing in a lot
of other areas, and the first bindweed and creeping thistle shoots started to pop up.
I realised that unless I sprayed everything with herbicide, growing any vegetables in
this space would be difficult and a lot of work, and I run the risk of having to
deal with these problematic weeds for many years. If I wanted to avoid herbicides, the easiest and
most practical solution would probably be to cover the entire area with ground cover fabric again,
including a perimeter around the beds, and leave it in place for a least a year.
It would be better to cover it with two layers of fabric to minimise light penetration even
more and reduce the chance of the sharp tips of the scutch grass piercing through the fabric.
Another option would be to cover two of the four beds with ground cover fabric
sheets that already have planting holes burned in them from a previous exploration.
I could transplant large brassica plants such as Brussels sprouts and purple sprouting broccoli,
through the holes and use cardboard collars or other materials to prevent the weeds from growing
up through the planting holes in the fabric. This way I could get a crop out of part of the
area this year, and also would be able to get a better understanding about how plants would
grow in each of the five no-till methods in the first year, which I think is important.
The other option is to remove a lot of the mulch material,
put down few more layers of cardboard, and place the mulch on top again,
but that would be a lot of work, and I would need a lot more cardboard.
The original aim of creating a no-till trial area was to use
several different methods to quickly and easily establish a growing space,
clear the existing vegetation and create excellent conditions or growing vegetables.
However, none of the five methods worked, and given the types of perennial weeds we have to
deal with, I’m not sure how this could have been accomplished easily and quickly in this situation.
Fortunately, we have plenty of other growing space, and more than enough to keep us busy this
year, so I'm not tempted to resort to the easy option of using herbicides to solve this problem.
But I would not criticise someone who did so, if they found themselves in a
similar situation that they needed to fix quickly. It was interesting to see how quickly the scutch
grass was able to regrow, and how much stronger it seemed than before I tried to kill it off.
The cardboard was not much of a barrier for this weed, but killed off a lot of the
competing vegetation, and the nutrient rich soil and mulch that we added on
top provided ideal growing conditions for this one weed to really establish itself.
This seems obvious now, but it’s something that I did not expect.
This has been very disappointing and frustrating, but I did set up the trial
with the possibility of failing, as I figured some of the weeds would make it through the cardboard.
And this has been a valuable lesson for me as we continue to develop more growing
spaces on weedy ground, and hopefully more people can learn from my mistakes.