One of the tasks that I end up doing over winter is to consolidate and analyse a lot
of the records and harvest data that we have collected over the previous season.
Although it involves a lot of time working at the computer, I like looking at the details of
all of the crops that we grew, to get a better understanding about what has been successful,
and what hasn’t worked out quite so well. And with this summarised data I produce,
I can compare the same crops grown in the different gardens, and in different years,
to understand the reasons behind the range of yields from all of the crops that we grew.
A lot of this fairly is intuitive in the gardens, while we are caring for the plants and harvesting,
but I have found it very useful to confirm all of this with data once
everything is harvested, and the crops cleared. One of the things that I notice is there can be
huge difference in the productivity between the different crops, and if I wanted to grow as much
food as possible it would make sense to focus on growing more on the most productive crops.
A quick look at the summary data could provide a simple answer to the question
of which of the crops is most productive,
but as usual a more detailed look provides a more nuanced answer that is more useful.
We try to weigh everything that we harvest from the gardens, recording it all in a spreadsheet
that can be filtered out for each individual crop. We also keep track of the amount of space that
each crop takes up in the gardens, so that we can calculate the yield,
or the weight of the total harvest divided by the area or size of space that it grew in.
And with a lot of the crops growing in several different gardens, and sometime
several batches of the same crop in each garden, there is a lot of summary data to work through.
The simplest way figure out what is the most productive crop,
is to find the average yield of each type of crop across all the gardens last season.
And looking at the information in this way, cucumber and chard
were the two most productive crops last year, and nothing else even comes close.
Cucumbers really are productive, given good conditions they grow quickly and can
produce a continual supply to harvest for a lot of the summer and into the autumn.
Chard is a very close relative to beetroot, which we grow to harvest the larger outer leaves and if
grown well enough to prevent them from bolting and going seed, they will continue to produce a
reliable supply of leaves for up to a full year. There are several different types of chard,
but I have found the Swiss chard type with the wide white stem and dark green leaves to be most
productive over the longest period of time. While cucumbers are very common, and the
abundance of the hot part of the season can be pickled and processed for later consumption,
chard is not so common or popular. But given its reliability and yield
even throughout the winter here in temperate Ireland, the more we learn
to love chard and to eat it regularly, the easier it will be to feed ourselves.
But that is just for the average yields from last year, and comparing them to the average
yields from all of the crops over the past 8 years that I have appropriate data for,
it is interesting to notice the differences. We seem to be getting better at growing
cucumber and chard, or at least able to harvest more on average from these plants.
And a few other crops such as squash, beans were also better than average this past year,
but only slightly, and a lot of crops are essentially the same,
even if there is a fair amount of divergences within each one type of crop.
But a few crops were not as productive this past season.
For some, such as turnip, parsnip, rocket or arugula, and kohlrabi,
the yield is smaller partly because we have been harvesting the crops earlier, to get
better quality, rather than waiting for a higher yield, which might not be as tender and tasty.
In other cases, such as with the parsley, we just did not harvest the crop enough last year.
But the biggest divergence is with the swede or rutabaga,
mainly because we had substantial crop failure last year.
Comparing average yields over many years, swede joins cucumber and chard as one of the
three most productive crops, and I think it is interesting that a fruiting crop,
a root crop, and a crop that we harvest leaves and stems from can all be really productive.
Of course we want to eat a lot more than just these three crops,
and a simple way of approaching this would be to grow more crops from one side of this list,
and give less space in our gardens or fields to crops from the less productive end of the chart,
if we want to grow as much food as possible in a given area.
And the average yield is a bit misleading as it includes batches that were really successful and
others that did not do well at all, and it also doesn’t take into consideration
the amount of time that it takes to grow the amount of food that was harvested.
Looking at all of the data in a different way, with the yield of each batch of each crop compared
to the number of weeks that it was growing, a more complex picture emerges, which I think
can give a better understanding of what is going on, if we can filter through all of the details.
Highlighting the different batches of swede within this mess of data, there is quite a difference in
the range of yields, as well as in the number of weeks that the crops were in the ground,
with the highest yields coming from the batches that were growing the longest.
But these older roots were not great quality when harvested,
as they became quite fibrous and in some cases had become rotten inside.
I would consider any crop that can produce over 10kg per square meter to be a high yielding crop,
but I would not really consider swede to be the one of the most productive crops we have grown,
or at least we haven’t been able to consistently produce a high yield of good quality roots.
The cucumber plants on the other hand have produced the largest
yields in a shorter period of time, with a few batches surpassing all the other crops.
But these heat loving plants only grow in the summer, and a bit of the autumn,
and in Ireland they will only grow well in the protection of a polytunnel or greenhouse.
We have also been training these vining plants up twine supported from the polytunnel structure,
which means that they cause overshadowing and reduce the yield of the crops beside them.
If I wanted to make a fair comparison, I should probably divide the weight of
the harvested cucumbers by a larger area, which would reduce the calculated yield significantly.
So, although they are a great crop to grow to take advantage of the heat inside a polytunnel
during the summer, producing a lot of cucumbers to eat fresh or to preserve, I am not sure that
they are the most productive crops that we grow. The chard crops in comparison are some of the
longest growing crops in the gardens, with the two largest yields from plants that
were in the growing in a polytunnel for more than a year before starting to bolt.
But even in the outside gardens, these chard plants can produce quite an impressive yield,
and are definitely worth growing for their reliability and consistency, but perhaps
there are other plants that are significantly more productive in a shorter period of time.
Looking at where other crops fit within this cluster of data, tomatoes are another plant
that we only grow in the polytunnels, and are consistently productive but long growing plants.
They are one of the few crops where it makes a significant difference when
comparing the amount of time from sowing the seed to harvesting the last tomato,
to the amount of time that the plants were actually occupying the bed in the polytunnel.
Subtracting the weeks that the plants were growing in pots, shows that they can be quite productive
in a reduced period of time, but they also overshadow other crops quite a bit.
The closely related peppers and aubergine or eggplant haven’t been as productive,
but we are working on that The climbing beans inside
the polytunnels and runner beans in the outside gardens can be quite productive,
but the yields should be probably adjusted down a bit to account for their overshadowing nature.
The other beans and pea crops are all relatively lower yielding,
even if they are very desirable plants in to grow in a vegetable garden.
And the squash plant that we grew up a trellis in the polytunnel last year produced a huge harvest,
much bigger than any other squash crop we have grown, but it also caused substantial
overshadowing, so the kilograms per square meter should be adjusted down quite a bit.
The related Courgettes or zucchini can also produce a lot, especially the plants that we
have been able to keep alive in the polytunnel, but because we tend to harvest them quite young
these plants don’t produce the huge yields that they could if we let them develop into marrows.
Looking at the wide range of leafy brassica crops, there are a few types of cabbages that I we have
been able to grow large yields of in a relatively short period of time, but most cabbages, as well
as the Brussels sprouts, and kales, produce a relatively low yield over a long growing season.
And the broccoli and cauliflower crops tend to be even lower yielding.
Carrots and parsnip can produce impressive yields if left to grow for the full season,
but we have found that beetroot can be a lot more productive in a shorter period of time,
especially because we tend to eat the full plant, roots, leaves and stems,
which substantially increases the yield of the young plants.
Potato plants can also produce a lot to eat, and we have grown very impressive crops of onions,
but neither of these are really in the running for the most productive crop.
Leeks and garlic and a range of herbs can be very valuable crops but do not produce
a lot of kilograms to eat compared to the area they take up, and the time they take to grow.
The wide range of leafy salad greens can be quite productive
over the long stretch of the winter months in the polytunnel,
and can produce a quick crop in a very short period of time, especially in the spring.
And by growing a succession of leafy salad crops like this, and other quick crops like radishes,
a huge yield can be produced over the full season from the same bed or section of the garden.
But it is the salad turnip, or Japanese turnip as we call them, that really stand out.
These are very fast growing plants of a hybrid variety of turnip,
which can produce a surprisingly high yield within 2 or 3 months after sowing the seeds.
The highest yields we have been able to produce came from plants grown in
the spring in the polytunnel, but they also produce really well in the outside gardens,
if the pests like flea beetle can be kept away. And like the young beetroot plants,
we include both the tender root, and the edible stems and leaves in the yield calculations.
So, in trying to figure out which are the most productive crops that we grow, I think it comes
down to a choice between the quick growing turnip and the more continually productive chard plants.
This hybrid variety of turnip is easily the highest yielding, in the shortest period of time,
but only if we eat the full plant, and if we eat the full plant, it significantly broadens
the nutrition that we get from this crop. But there are definite benefits from a
crop like chard, where we can sow once and harvest over a long period of time
from hardy plants that generally don’t have any issues with pests and diseases.
And with shelter from damaging wind either with a polytunnel or som other form of protection in the
outside gardens, both of these plants can provide valuable greens to eat throughout the winter.
While the turnip and cucumbers need to be harvested over a relatively short period of time
to get the best quality, the leaves of the chard plants can be left for quite a long time, making
the timing of harvesting much more flexible. And that is probably one of the key reasons
why they have been a staple crop in our gardens for many years.
We are currently harvesting from a crop that was direct sown into a side bed of
one of the polytunnels last June after an early crop of potatoes was dug out.
We started harvesting leaves from these plants from the end of July, and continued to harvest
throughout the autumn and into winter, thought the growth definitely slowed down with the cold
weather and the lower light levels. But in the last few weeks the plants
started growing really quickly again, with huge amounts available to be harvested.
So far we have harvested 90 kg from this 3.2m2 bed, which translates into a yield of over
28kg of high quality leaves and stems per square meter, and there is still a lot more to harvest.
The plants look like they may be stating to transition into producing a large seed stalk,
and although the leaves can still be harvested for a while after this happens,
the yield and quality definitely drops off.
But there is probably still a few more weeks of harvesting left, and this one
batch of plants will probably become one of the most productive crops we have ever grown.
And if we learn to love chard, as well as turnip, and we eat it very regularly,
then it will become significantly easier to feed ourselves and a lot of other people.