Last year I decided to stop growing vegetables
in my new polytunnel space, in order to deal with a few problematic issues. The plants last spring didn’t do very well,
and there were some deficiencies apparent in the crops, and there was signs of a viral
disease in the tomato transplants. I also felt that I didn’t have enough compost
to adequately prepare the soil in these garden beds for the level of production that I wanted. So I decided to pull the crops, remineralise
the soil and sow a green manure or cover crop, in order to build the soil organic matter,
improve the soil biology, as well as improve soil texture. I don’t have a lot of experience in growing
this types of crop cover in my gardens, but it’s something that I’m really interested
in exploring a lot more. And I’ve never grown a green manure in the
protected climate of a polytunnel, especially over the winter, and it was interesting to
see how it all turned out. My plans were further set back by severe fire
damage to the polytunnel, after which the entire sheet of plastic had to be replaced. I took the opportunity to level the beds some
more and to clear out a lot of the weeds, and I added a range of concentrated fertility
and mineral amendments, including a lot of chicken manure. This was all part of the process of starting
to fully remineralise and balance the fertility of the soil, based on detailed soil tests. It was late autumn by the time I sowed a mix
of green manure seed, which was specifically developed for overwintering in the Irish climate,
and included wild rye, black or Japanese oats, vetch and two types of clover. Because I had added so much chicken manure
to this soil, I was not so concerned about the nitrogen fixing capacity of this green
manure, but some more would definitely be good. I was much more interested in growing carbon
and building organic matter both above and below the soil. I was also interested in growing plants with
strong vigorous root systems which would work to improve the structure of the soil, both
within the top soil and deeper in the soil profile, and a big part of this was to bring
life back into soil, to boost the soil ecosystem. After broadcast sowing the seeds and working
them shallowly into the soil, I set up a dripline watering system back onto beds. I then I finished off the preparations of
the growing space by adding wood chips onto the paths between the growing beds. It was really good to see growing space clean
and well established, especially after the problematic events of the season. The growth of the green manure was slow at
first, but the young plants grew steadily over the winter which was not too cold and
the polytunnel offered protection from the windy weather. As expected the growth rate accelerated in
the early spring as temperatures began to rise again with the longer days and more sunlight,
It because quite an amazing stand of vegetation, quickly reaching knee high, then waist high
with some sections and plants going even higher. But the growth wasn’t even across the full
garden, indicating possible differences in the underlying soil fertility or soil structure,
and a mould developed on the leaves the rye or oats, especially at one end of polytunnel
space. This indicated to me that something was not
quite right, though I’m not sure what it was, but the humid conditions and lack of
strong air movement in the enclosed space probably contributed to this issue. There was also lots of other plant species
mixed in, including the various types of annual weeds that are typical in my gardens, as well
as a lot of leafy brassica plants, which had self seeded and cross pollinated when this
growing space was abandoned a number of years ago. I think that the more diverse range of species
can only help, so long as I could get rid of the plants when I needed to. One of the big issues with green manures is
how to get rid of these typically strong and vigorous plants so that we can grown other
crops. Green manures like this are traditionally
dug or ploughed in, or chopped up with a flail mower, in order to both kill off the plants
and to incorporate the carbon and nutrient rich biomass into the soil for quick decomposition. I have wanted to transition this polytunnel
into a minimum till, or no-dig, growing space, with only minor surface cultivation from now
on, so digging wasn’t a preferred option, and I don’t have access to a flail mower. But I was planning to cover this entire garden
space with ground cover fabric, with holes in it for tomatoes, cucumbers and other crops,
and I figured I could simply cut the strong growth of vegetation, and leave it on the
surface of the soil to decompose over time, underneath the ground cover fabric. With the this fabric, preventing the regrowth
of the plants would be relatively easy, but I still had to figure out a way to cut or
flatten or trample all of the vegetation, and I figured the best option was to use my
scythe to cut it all down. As I wanted to allow as much biomass to grow
as possible, I waited quite late, until a lot of the plants were starting to flower,
and then I used my scythe to slowly and carefully cut the dense growth of plants. I was extra careful along the edge of the
space to avoid cutting into the plastic, and I managed to do the full job without a scratch. But I wasn’t careful enough to avoid the
dripline watering pipes, and sliced through the pipes a few times, but thankfully they’re
quite easy to repair. It probably would have been better to take
the time to pull out all the lengths of dripline pipe entirely, or in hindsight I should have
installed an overhead sprinkler system instead, when I originally sowed the green manure,
which would have made the whole process easier. I laid all of the cut material or hay onto
the garden beds, and then covered the full garden with the sheets of ground cover fabric
that already had holes in it from a previous season for the plants that I wanted to grow. For the beds that I was planning to transplant
into right away, I moved a lot of the hay onto the paths adjacent to the bed, to make
it easier for transplanting, and I figured that the material would be broken up and crushed
as I walked back and forth, which I think would have speeded up the decomposition. In hindsight, I probably should have done
this right away with all of the hay material, to crush it and mash it underfoot for a while,
before putting it back onto the beds, which I think would have really helped. I then marked out the location of each hole,
pulled back the ground cover fabric, and then dug over the stations for each plant, chopping
up the remains of the green manure stems and the root systems in the process. While this was going against my preference
for reduced cultivation, it was only a small portion of the volume of soil, and it made
it a lot easier to transplant the tomatos through the holes in the ground cover fabric
once it was put back in place. When the plants were a little bit more established,
I lifted up the edges of the ground cover fabric, and scraped the crushed remains of
green manure material, back onto the beds, where I figured it would act as a type of
side dressing for these heavy feeding plants during the growing season. As the plants grew bigger, it was interesting
to see the roots growing right into area where the the decomposing biomass was touching the
surface of the soil. This mulch, under the ground cover fabric,
allowed the roots of the tomato plants to colonise the whole volume of the soil and
then some. Unfortunately, a short time after transplanting,
the tomato plants were showing signs of nitrogen deficiency, indicated by a pale discolouration
of the older leaves. It was only then that I realised that most
of the nitrogen that was in the soil had been incorporated into the roots and leaves of
the green manure. I had thought that a fair amount of the fertility
would have remained in the soil, but apparently most of it was used up by the strong growth
of these green manure crops. And the process of decomposition hadn’t
started to release the nitrogen yet, or at least not fast enough for what these young
tomato plants needed. I fed these plants with a liquid feed of a
high nitrogen fertiliser and then foliar fed them a few times over the next few weeks,
and a month later they were growing really strongly. In hindsight I should have provided a liquid
feeding while transplanting, and it would have been even better if I had mixed in some
compost when I dug the stations for each plant, and I made sure to take these precautions
with the other plants that I transplanted a few weeks later. I assume that cutting the green manure material
a few weeks earlier would have partially alleviated this issue, but it would have been even better
to have dug the green manure into the soil in the first place which would have sped up
the decomposition, and released the nitrogen and other nutrients closer to the roots of
the tomato plants. Of course digging it in would have further
delayed getting the possible benefits of a no-dig soil ecosystem in these beds, but even
partially digging it in would have helped to speed up the transition from green manure
to crop. No doubt this blanket of biomass will continue
to feed the soil biology and plants with a gradual release of nitrogen, carbon and other
nutrients over the long growing season, rather than a quick flush of fertility at the beginning
of the season. I suspect that this slow and steady decomposition
is probably a good thing, but it is something that I definitely want to keep eye on as the
growing season progresses. Overall I still think it was beneficial to
take the time to grow a green manure to help to improve the quality of the soil in this
valuable growing space. Button course it would have been much better
if I had established the beds and then grown a green manure for at least a year before
putting up the polytunnel in the first place. But growing in the shelter of the polytunnel
did allow a lot more biomass to be produced in a cold part of the year, and I could have
grown an even wider range of species. Using a sprinkler watering system instead
of drip line would have made everything easier and would have prevented the hay from drying
out, which would have helped to speed up the decomposition. If I was to do it again I would consider using
a mulcher or a lawnmower to cut the green manure a few times while it was growing, or
even scything it a few times. A more gradual buildup of organic matter on
the surface of the soil, in layers over time, might have worked better, and would have avoided
the huge amount of biomass at end. Or I could have cut the green manure a few
weeks or even a month earlier to allow the decomposition and soil to settle before transplanting. But this would have significantly reduced
the amount of organic matter that this crop of green manure would have reenable to produce,
which was one of the main reasons for growing it in the first place. No doubt there is a balance there somewhere,
or a more suitable method, in trying to grow as much organic material as possible, without
negatively impacting the following crop, and I’m not sure that I found it on my first
try. This video was all about growing a green manure
in a polytunnel, and then getting rid of the green manure so that I could grow another
crop. I’m planning to make another video in the
near future, where I’m going to explore the question about whether it was worth growing
the green manure in the first place, compared to other options that I might have had. If you’re interested in this kind of thing,
keep an eye out for that video, and perhaps subscribe if you haven’t already. This process of trying things out, and then
questioning and wondering whether it was worth it, or how to be able to do it better, is
a big part of this RED Gardens Project. If you value this approach, and want to support
me in this endeavour, I’ve identified a few options in the description below. Any financial support that you can give would
be greatly appreciated. But the biggest support that you can give
is of course continuing to watch my videos, and thank you for making it all the way to
the end of this one.