I’ve been growing vegetables in this polytunnel for about 8 seasons, and it forms one of seven
family scale gardens that that makes up a major part of this RED Gardens Project.
I've found it to be a great space for growing the heat loving summer crops, which would
otherwise be very difficult to grow in the maritime climate of Ireland.
I've also been exploring the possibilities of growing in this covered space all year
round.
Over that time, I’ve come to believe that perhaps the most valuable use of a polytunnel
space in this climate is to grow crops for harvesting in late spring and even into early
summer, when not much is available from the outside gardens yet, to fill what is commonly
referred to as the hunger gap.
Although it can be a bit difficult to find a balance between getting the most out of
this garden for each season, I've been learning a lot over the years, and getting better at
growing the spring crops.
Looking back at the harvests so far, I’m really pleased with a lot of the spring crops
this year, and some of the yield data is quite remarkable, I think.
The main strategy within this garden is to be able to harvest vegetables all year round,
which means planting types of crops that are not normally grown in a polytunnel.
Broad beans or fava beans are a good example of this, and I really hesitated growing this
crop, which seemed too low yielding for such high value growing space, and they usually
grow so well outside.
But I was surprised that I was able to harvest over 30 kg of pods from this 4 m2 bed, which
translates to 7.5 kg/m2, but that is for the full pod.
If I was to weigh only the broad bean seeds themselves, this would reduce the yield to
about 2.5 kg/m2, which is low enough, but on the other hand to get 10kg of broad beans
seeds from a relatively small area of the garden is quite impressive.
Garlic is also an unusual vegetable to grow in the polytunnel, but I've found that the
bulbs can grow so much larger than they do outside, perhaps too big.
Once the plants had dried and cured, the yield this season was almost 3 kg/m2, which is less
than most of the other vegetables I would grow.
But to get 7.5 kg of garlic from a small 2.5 m2 bed is a lot, and more than enough garlic
for most people for full year, so it's definitely worth growing.
Onions are also a relatively unusual vegetable to grow in a polytunnel, especially the storage
variety, but this season they were at the other end of the scale in terms of yield,
with about 11 kg harvested from each square meter.
It's also very useful as get a much earleir crop than Is available outside, especially
when some of them are harvested as green onions, as it helps to fill the gap in onion supplies
between one year and the next.
The root vegetables are usually really productive in the protection of polytunnel in the spring,
as they can grow so quickly.
This was especially the case this season, where yields ranged from 15 kg/m2 for beets
and only 7 kg/m2 for kohlrabi, which technically is more of a swollen stem than a root, but
I include it anyway.
The crop of turnip and carrots were in-between the two, but with all these plants the longer
you leave them the bigger they can grow, but the quality of the root can suffer as the
size increases.
This was my first season growing a particular hybrid variety of turnip, and it was definitely
tastier when harvested smaller, and I have found the same to be true with kohlrabi.
The beetroot and carrots on the other hand retained an acceptable quality as they grew
larger, but it really depends on what you want, and how much time is available before
needing the space for other crops.
Another important factor with all these crops is that the yield I calculated was for the
full plant including the stems and leaves, and if I just weighing root then the yields
would be lower, bit still quite good.
We tend to eat all the stems and leaves of the beet plants, and have been pleasantly
surprised by the quality and taste of the turnip leaves, but we don’t eat kohlrabi
leaves, and only occasionally eat some of carrot leaves.
More than many of the other types of vegetables, the harvestable yield really depends on what
you want with these root crops.
The leafy salad greens are also great crops for growing in the spring in the polytunnel.
I have been exploring a number of different methods for growing a range of different types
and I typically got around 5 kg/m2 out of these salad type crops, which is really more
than it sounds like, as one kilogram is a lot of salad leaves.
They can produce over a reasonably long period of time, but a lot depends on the weather
and how well I manage these crops, as they all have a tendency to bolt or to start the
process of producing seeds.
One related crop that I have been quite surprised with this season’s is a variety of kale
that I have been growing and harvesting as a type of salad crop, and this one bed produced
more than 10 kg/m2 of small and medium size leaves.
The plants seemed very resistant to bolting, and I only pulled them up to make space for
the next crop, and I wonder how long these plants would have continued to produce fresh
kale leaves.
Potatoes are another crop that grow well outside, but with the threat of late frosts, I find
that I can produce a much earlier crop of potatoes by growing them under cover.
This season I tried growing 6 different varieties of early potatoes, which I harvested over
a 5 week period of time, and the average yield was about 6 kg/m2 or about 1 kg per plant.
This is a lower yield that lots of other crops that I could grow over the same period of
time, but this is calculated or evaluated on a kilogram or weight basis, which is perhaps
a bit unfair, as potatoes are generally seen as a carbohydrate or calorific crop.
It would be interesting to calculate the harvested yield in terms of calories/m2, as I imagine
the potatoes would come out much higher than most of the other crops that I’m growing.
The spring crop of broccoli seemed to be quite good this year, but only produced 4.4kg/m2
of large central heads and a few secondary side shoots.
The plants probably could have produced more side shoots, but I was anxious to remove this
crop so that I could get the eggplant or aubergine plants transplanted into the bed instead.
While most other crops can be harvested earlier, with this type of crop you have to wait until
the edible flowering head is produced before you can harvest anything.
Because I have to delaying the subsequent crop, and with not a great yields, I do wonder
if it is worth growing this type of crop at all.
The adjacent Cauliflower crop was quite different though, and I was surprised that it had almost
double the yield of the broccoli plants, with more than 8 kg/m2 of edible central heads
harvested at the same time period, and the quality of the crop was really good.
This was my first year growing microgreens in the soil beds of the polytunnel, and I
was pleasantly surprised how productive this very quick crop can be.
Some of the better batches produced in the region of 2.5 kg of high value mixed microgreens
from each square meter of bed, within 3 or 4 weeks after sowing.
And as the temperature warmed as the spring progressed, the length of time between sowing
and harvesting dramatically decreased.
A had a few pest issues which reduced the yield, and took some time to figure out how
to avoid, and I had also significantly overestimated the amount of time that I would need between
batches on the same section of soil.
Overall I was able to harvest a bit more than 4 kg/m2 from this first trial on one section
of the garden, before I needed the bed for the cucumber crop, and this is still a lot
of microgreens.
But I have calculated that I might have been able to harvest as much as 10 kg/m2 from a
quicker succession of sowings, before the bed was needed for the summer crop, and it
will be interesting to see if I can get this type of yield next season.
This was quite a wide range of crops, with different availability for when they were
harvested, and different lengths of time between sowing and harvesting.
There was also a wide range of yields, but I'm not really comparing like for like in
some cases, as a kilogram of one crop is not really the same as a kilogram of the other,
both in terms of nutrition that you can get out of it and often quite different in terms
of personal preference.
But I think all of these crops were quite successful, and it was really nice to get
the diversity.
The hybrid variety of turnip that I grew definitely produced the highest yield in the shortest
period of time, as well as doing better in the cooler part of the spring, and I was quite
impressed with the growth and the taste of this crop.
But it was the beets that produced the highest overall yield, even if these plants did occupy
the garden bed over a longer period of time, and it is one of my favourite vegetables.
The 15 kg/m2 of beet roots and greens that I was able to harvest, is a lot of food to
get out of a garden, especially when there is still lots of time in the season to grow
another crop or even two on the same section of garden bed.
I have a general target of wanting to harvest at least 1000 kg or more than a tonne of a
diverse range of vegetables from this garden, over the full 2019 season, and a comparable
target of wanting to harvest at least 500 kg from each of the outside gardens.
While each of these gardens covers a total area of 100 square meters, there's only about
67 m2 of growing beds in this polytunnel garden, once you exclude the paths.
So to hit this target of 1000 kg, I would need to harvest on average about 15 kg of
vegetables from each square meter of bed over the full season, and with the beet crop I
reached the target with just one crop in only part of the season.
The crops of kale, onions, turnip, cauliflower and carrots all produced more than half of
this target, and the broad beans did as well if i include the pods
In total, I’ve already harvested over 500 kg from this garden, including all of these
spring crops and a few overwintering crops, which is more than half of the target for
this garden.
500 kg also already matches what I want to be able to harvest out of each of the outside
gardens, and this shows the real benefit of growing under the protection of polytunnel
plastic.
It’s been a good start to the season for this garden, and there's still a lot more
to harvest over the summer, autumn and into the winter.
I think it's useful to ask why the yields in this polytunnel garden have been so good
for the first half of this season, even better than in previous years.
The weather had been quite good, with generally warmer than average conditions over the winter,
and then a relatively cool spring, and it didn’t get hot until the end of June, and
this was perhaps the biggest factor.
The protection of the polytunnel plastic in these conditions, would generally have boosted
the temperature into a range that provided good growing conditions for most of these
crops, without it getting so hot that the plants became stressed.
In addition, the levels of fertility and soil quality in this garden have been gradually
improved and I think that all of the work I've put into building the soil is really
paying off this season.
While there was some disease and pest pressure, it wasn’t generally enough to reduce yields,
except with the microgreens, and this was helped with the new sprinkler system that
I installed, which has made it a lot easier to maintain good soil moisture levels.
Different crops and better varieties have also contributed to this increased in yield,
and I'm also getting better at managing a lot fo these crops.
This involves knowing when to sow, and how to care for the different types of plants,
and when to harvest so that I can get large yields of good quality crops, and also how
to keep the garden relatively clear of weeds.
I still have some work to do in developing the skills and knowledge that are needed,
but I feel that I'm definitely becoming more successful in managing the particulars this
garden through the spring and into the summer.
And a lot of this comes down to planning, and doing what needs to be done, when it's
the best time to do it.
This Polytunnel Garden is one of 7 family scale gardens that I’m experimenting with,
that together with the larger Black Plot that I’m developing, form what I call the RED
Gardens Project.
This is an independent, citizen led, research and development project, focused on trying
to encourage and support other people to grow more of their own food.
The only external funding that this projects receives is through the sale of surplus vegetables
to my neighbours, by people like you watching my videos, and through direct donations and
contributions through my Patreon and PayPal accounts.
I’d really like to thank those people who have decided to make regular contributions
to my project, through my Patreon account, or once off donations through PayPal.
If you’d like to join them, any contributions would be greatly appreciated, and I’ve left
links to these in the description below.
But most importantly, thank you for watching.