Polytunnels are a very high value growing space, especially in the climate that we have
here in Ireland, but they are expensive enough to put up. And like all gardens it's important
to continue to improve the growing conditions and soil fertility, and over the years I've
learned that it's definitely worth putting in the extra effort and resources in order
to be able to get the most out of the initial investment of this protected growing space.
With my older, slightly smaller polytunnel I've had a continual rotation of crops year round,
so that there is always something growing, which means that I tend to amend the growing
beds in sections as they are emptied of one crop and before another one goes
in. But in my newer polytunnel I didn't manage to plant any overwintering crops last year,
which has the advantage of giving me a clear space to work in, so that all of
the preparation work for the season can be done at once. So over the last few weeks we've put in
the effort to clear the space, amend the soil, make some improvements to the infrastructure,
so that this polytunnel space can be made ready for the new growing season.
Four years ago I put up this polytunnel on rough ground that took a lot of work and some help
with ground cover fabric to manage, but I got good results in that first season of growth. The second
season started with too many weeds, fertility issues and problematic diseases, so I decided
to abandon the crops, and to work on improving the soil before growing anything again. Later
in that same season, the plastic of this polytunnel was severely damaged when the adjacent
compost facility burned down, so I ended up replacing the plastic, re-establishing the beds,
and sowing an overwintering green manure. After working in the green manure the following spring,
and recovering with ground cover fabric I was able to get a reasonable crop in 2019. To start the
season last year I decided to manage the fixed beds with minimal cultivation or a version of
no-dig, and I remineralised the soil and covered the beds with a thick layer of compost. Last year
I was able to get a large harvest of spring and hunger gap crops, as well as an abundance form
the summer and autumn. So 2021 started with the garden in reasonably good condition, and
we had the time over the winter to do the work of clearing out all of remains of last years crops,
apart from a few parsley plants as they seemed worth keeping for a few months of production into
the spring. And the first job after clearing out all the plants and weeds was to redefine the edges
of the fixed beds with twine stretched between two stakes at either end, and although this took
a bit of time to set up it makes the rest of the work in this growing space a bit easier.
The main addition to this garden again this season was to spread a generous layer of compost over the
surface of all of the beds. I have joined in with the local community farm to order a large
truck load of finished compost, and it's been great having this resource of clean, weed free,
and easy to manage organic material. Moving this volume of material is a fair amount of work,
and the pile is about 100m away from the polytunnel, but I've found that the easiest
and most convenient way to do this job is to load the compost into buckets that are then
set into a cart and hauled down the path to the polytunnel. It is then easy to use the buckets
to spread the relatively free flowing material and to get a fairly even distribution over the beds,
and I find this is a lot faster and easier than shovelling compost into a wheelbarrow. We ended up
adding a total of 2.5 cubic meters of compost as a base layer, giving a depth of compost about 30mm
or 1.25" once raked out evenly over the surface of the 80 square meters of growing beds. I think this
is a reasonably generous amount of compost to add each year, and close to recommendations from other
growers, but I haven't done any real explorations to figure out what might be an ideal amount.
Before adding the compost to the surface of the soil I had taken an overall soil sample from this
garden, and I plan to use the results of the detailed soil test to continue the process of
remineralisation and balancing this soil, but I have been delayed in getting it sent to lab. So
until I get the results I've added a base layer of concentrated fertility amendments
including 10kg of chicken manure pellets to top up a lot of the main nutrients,
which works out at about 125g per square meter of growing bed {?oz/ft2). I also added 2.5 kg
seaweed for trace elements, and a smaller amount of sulphur as a key mineral that I have found to
be in short supply in these soils. All of this was spread over the top of compost as I feel that this
compost that we bought was not so rich or fertile, and could benefit from being amended as well,
and a lot of the fertility will wash down into the soil and hopefully be distributed by worms
and other soil biology through the topsoil. I then covered the beds with an additional thin
layer of compost so that the amendments were not on the surface, and this brought the total amount
of compost added to about 3 cubic meter [or 3000L or 4 yards] resulting in a depth of about 40 mm or
1.5". When the results of soil test come back, I suspect that it will show a deficiency of
phosphorous and a few other trace elements like boron, copper and zinc, and I will probably amend
these later in the spring with a side dressing or dissolved in water and sprinkled over the beds.
No doubt I will be foliar feeding and liquid feeding some of the plants during the
growing season and I might even side dress with additional compost and fertility at some point,
but I think that this initial addition of fertility and compost
will provide enough food for the soil and plants for most of the growing season.
With all the compost added, the surface of the bed raised even further above the level of the
fixed paths, which I filled in with wood chip, partially to prevent the compost from falling
off edge of bed. I've used other types of wood chip in the past, but this time I was able to
salvage decomposing wood chip and sawdust from the base of the hopper of our district heating system,
which had gotten wet at one point and was starting to decay. This material had lots of fungal mycelia
in it, and a few months exposed to the winter rain accelerated the decomposition process. I
was able to add a bit more than one cubic meter of wood chip to the paths,
which produced a layer of about 30mm deep, which will keep the soil moist, suppress any weeds and
provide a much cleaner surface to walk on. And over time this abundance of carbon will decompose
further and feed the soil, and no doubt I will top up the paths with more wood chip next season.
During all of this work I decided to leave the network of drip line pipes in place
rather than pulling all the pipes to the side or out of the polytunnel completely. I
wasn't sure how much they would get in the way, but the thick layer of compost
that was added initially was enough to temporarily bury the pipes. I did think
about keeping them buried in compost for the full growing season, but I noticed that with
the contraction and expansion as the pipes heated and cooled in the sun,
they pulled them out of compost anyway. In hindsight it would have been a bit easier if
I done all work in short period of time, to get it finished before the pipes started to move a bit,
as it was a bit of a hassle to rake the beds flat when they were no longer buried in the soil.
I tested the drip line system and flushed out the pipes in case any debris had gotten in, and
then taped up the ends again. I found one hole in one of the pipes, and I'm not sure how I made it,
but it was easy enough to fix with tape as this is a system of leaky pipes anyway, so an additional
leak is not an issue so long as it isn't too big. Once all of the amendments were added to the beds,
we pulled out the drip line pipes so they can lay on the surface of the compost
and any of the disturbed compost could be easily levelled by hand before sowing the crops.
The main improvement that I made to the infrastructure of this growing space this season
was to install a sprinkler system, in addition to the drip line system, for watering the
plants and the soil. There are benefits and issues to both of these watering systems,
but I have experience in my other polytunnel that they compliment each other quite well. The
sprinklers are very useful for watering the entire space of the garden, which helps in
the spring when the polytunnel is full of lots of small fast growing salad type crops, and the
drip line system works well for watering without increasing the humidity in the space too much,
especially when taller crops like tomatoes will get in the way of the sprinklers. These sprinklers
are a useful example of a complete system that has been designed for easy installation
and although systems like this can be expensive, it is going to save time and effort over quite a
few years, and hopefully result in better crops, so I think it is worth the investment. I put in
two lines of sprinklers down the length of the polytunnel, with the pipes hung from polytunnel
frame on simple wires, which allowed me to set them at whatever height I wanted. One
issue that I have to take into consideration was the fact that there is currently quite low water
pressure and flow on the site due to a blocked pipe, but we anticipate this being fixed in the
next few months. And from my experience with my other polytunnel, the current pressure of the
water would not be enough to effectively run the full line of 15 sprinklers, and definitely not
the two lines of 30 sprinklers. To get around this temporary issue, I installed a valve to
split each lines into two, and installed a connector at each end of each pipe. So
for the next few months I can effectively water one quarter of the polytunnel space at a time
and simply connect the hose to each pipe end in turn to water the full space.
Once better water pressure is established, I can then leave the valve open,
connect the pipes together and join them in with the drip line network
so then I only need to use a valve to switch between the two systems,
and I'll probably end up installing a timer to make the regular task of watering even easier.
The thick layer of compost and wood chip will prevent a lot of the existing weed seeds in the
soil from germinating, and weeding is definitely becoming less of an issue in this growing
space. Last year I added the layer of compost a few weeks later in the season, and found a lot
of weed seeds had already started to germinate and ended up coming up through the compost. We
will see if the same thing happens again this year, but I expect that it will be a lot less
because the soil hasn't been cultivated underneath the compost, so a new batch of dormant weed seeds
hasn't been brought closer to the surface of the soil, and we have prevented any weeds from
dropping any new seeds in the space. I've also cleared out most of the perennial weeds roots
over the past few years, but there is still a few patches of creeping thistle and scutch grass
and a bit of bind weed at the edges. I need to be persistent at pulling out any growth that does
appear in order to continue to weaken the roots and prevent them becoming established again. This
year I also need to put in the effort to clear out the area around the outside perimeter of
the polytunnel as some of these roots can find their way back in under the buried
plastic. Eventually, if I keep up this kind of management, this will be a largely weed
free growing space, which will significantly reduce the amount of work I need to put in.
The final thing that we need to do to prepare this growing space for the season is to finish
washing the inside and outside of the polytunnel plastic. The main purpose of this is to allow as
much sunlight as possible to get into the growing space, but also to reduce the risk of any moulds,
spores and other diseases spreading to the crops, and I also suspect that it will help
the polytunnel plastic last longer, but I am not sure about that. We generally use a soft
brush or a broom and hose to clean the inside of the plastic, but we use a wet towel attached to
ropes that can be pulled back and forth over the outside surface of the polytunnel. This
is one of the few jobs in the gardens that is easiest to do when it is raining quite a bit,
but a hose works as well, and I'm going to try do this cleaning several times during the growing
season, as I suspect this will be better and easier than leaving it to only once a season.
It's great to get this polytunnel ready for the new growing season, but there's still a bit of
work to do in clearing all the vegetation from around the outside of the structure,
reworking the water system once the pressure improves, and adding additional amendments
and fertility once soil test results come back. But it is ready for planting and I've already
started sowing a succession of fast growing crops for spring and early summer harvest. I've also
planted some strawberries plants in part of one of the beds, which will stay in place for at least
the full year, to see how they produce in this enclosed space compared to the outside gardens,
but most of garden will be planted up with warm season crops again by the summer.
And this year I plan to sow some overwintering crops, after the main
warm season crops are finished in order to have an abundance to harvest at this time next year.
But before those late sowings I will probably add another layer of compost to the surface of
the soil, and do another round of cleaning, preparation and adjustments, so that I can
continue the process of gradual improvements to get the most out of this high value growing space.