There are often spaces in a garden that need to be filled in, but in many cases it seems
that there’s just not enough time to fit in another crop, or I may be uncertain about timing.
When trying to grow a succession of crops I often find that I’m impatiently waiting
for one crop to mature enough to get a reasonable yield, before the next crop can go in.
As a way of managing this, I’ve started to sow leafy salad crops to fill in the gaps,
as both a harvestable yield and as a form of fast growing cover crop, and it seems to
be working quite well.
My inspiration for sowing edible cover crops comes originally from Steve Solomon, in his
book ‘Gardening When It Counts' where he talks about sowing peas, spinach and other vegetables
as a form of cover crop, which could be harvested or not depending on the circumstances.
We usually think of cover crops as being the types of plants that we would not normally
eat, they are grown to protect, develop and feed the soil, and to benefit the following
crops, not to feed us directly.
On the other hand, we tend to want to harvest as much as possible out of the crops that
we do sow, and to grow them is such a way so as to maximise what we can eat, and then
to pull them out as soon as the’ve stopped being productive, so that another crop can be grown.
It’s interesting to rethink a cover crop as something that can be a malleable hybrid
between the two, depending on context, timing, and the available of other things to eat during
the same period.
So, I’ve begun trying out this type of hybrid approach in a few places, using various forms
of broadcast sown salad greens, and have been quite successful this past spring using this
method in my family scale Polytunnel Garden.
There were a number of different empty spaces in this covered garden this past spring.
Some of them were gaps between the overwintering crop and the summer crops, and for some I
just didn’t get other spring crops sown early enough and I felt that there wasn't
enough time for them to mature.
I broadcast sowed 4 different types of leafy salad greens in 10 different patches.
There was 4 batches of spinach, 3 batches of rocket or arugula, 2 batches of a mix of
spicy brassica greens, and one patch of red russian kale.
None of these plants will fix nitrogen, and the potential benefits of reducing erosion
or preventing the leaching of nutrients isn’t really relevant in this covered garden, assuming
of course that my watering isn’t too aggressive or excessive.
But all of these crops are very fast growing, especially in the sheltered warm climate of
the polytunnel, producing lots of tender organic matter for eating, or for composting.
Hopefully they will keep the soil biology quite active with their root secretions while
growing, and leave the soil in great condition for the following crop.
The four batches of spinach that were sown had quite different outcomes.
The first and largest batch was sown early enough to avoid the real heat of the start
of the summer, and I was able to harvest a lot from it, first through thinning young
plants and then picking individual leaves.
And then, 53 days after sowing, I removed plants from the centre of the bed to make
space for transplanting in the tomato plants, and only removed the remaining plants when
they started to produce a seed stalk.
This was a really productive crop, producing more that 16kg of spinach, or more than 4kg/m2 of bed,
but because I prioritised harvesting, not so much organic matter was produced for the compost.
The second batch covered a smaller area and I focused on thinning this crop quite a bit,
pulling out whole younger plants for eating, to ensure that the remaining plants had lots
of space to grow.
This patch produced more than 5kg/m2, before the heat of the summer caused them to bolt,
but then I left the plants in the ground for another 2 weeks to produce an abundance of
organic matter before they were removed to make space for the climbing beans.
This was probably my most successful planting of the spring, with a decent balance between
a large harvest and gaining the benefits of the cover crop, with lots of organic matter
produced for the compost.
The third batch was sown almost a month later, and it struggled in the heat.
I didn’t thin this batch at all, and I harvested a bit by cutting the carpet of smaller leaves,
but I then left it as a flowering cover crop, the same as the second batch.
The fourth batch of spinach was also sown quite late, and had poor germination to start
with, leaving gaps in the bed.
I transplanted the courgette or zucchini plants in among the spinach, but in hindsight, I
should have cleared the remains of the crop earlier or left a larger space for the courgette
plants, as they seemed to struggle more than they should have.
With the three batches of rocket or arugula I struggled to find a balance between harvesting
lots, maximising the benefits of the cover crop and prioritising the plants that were
to be transplanted into the same bed.
The first batch was broadcast sown reasonably early in the season, and as the plants started
to bolt I cleared spaces to make room for the calabrese and cauliflower plants, and
they shared the same area of the garden for another week or so.
I wonder if this strategy of overlapping the crops is a useful one.
The shade provided by the cover crops probably helped during the hot weather and these plants
did produce a lot of biomass over that period, but the transplants may have become overcrowded.
The second batch was sown a few weeks later, and I was able to harvest a lot, as well as
growing a lot of biomass.
I only needed to clear a small section of the bed for one squash plant to be transplanted
in, and the two crops grew side by side for 9 days.
It was remarkable how much biomass was produced by the rocket plants in that time, and I tried
to keep the abundance of growth from overwhelming the squash plant, but perhaps I could have
cleared more of the space for the squash.
I should have also cleared the 3rd batch of rocket earlier than I did, to make room for
pepper plants, but I don't really have a lot of other salad crops available at this time,
so I've shifted priorities to maximising yields and leaving the rocket in place for longer.
So far, I've harvested 6.3kg or about 4kg/m2 from four cuttings using the cut and come
again method, and it looks like it could produce another cutting, but those pepper plants really
do need to get into the ground.
I sowed two batches of a mix of spicy brassica greens, including mizuna, mibuna, two types
of mustard leaf, and a few rocket seeds sown in for good measure.
The first batch was similar to the first batch of spinach, with half of the crop being removed
to make way for the tomato transplants, and it was managed in a similar ways and had very
similar yields of 4kg/m2.
But I think in this case, the spinach crop was better, as it was less disruptive to the
soil when the plants were finally removed.
The second batch of mixed spicy greens is still going, with 3kg/m2 harvested already,
and I still have some time before the bed is needed for a later sowing of courgettes or zucchini.
But I have a lot of similar salad crops available from my outside gardens, so I will likely
leave this bed to grow on as a flowering cover crop, hopefully attract lots of pollinators
into this covered garden.
I think the most interesting batch of broadcast sown greens this spring was of Red Russian
Kale, partially because I haven’t growing kale as a salad crop before.
The batch was the first one sown, was slower to become established, but lasted longest
without bolting.
Similar to one of the batches of rocket, I cleared a spot for a squash plant and let
the two crops grow side by side, but I continued to harvest the kale leaves right up until
the remains of the cover crop were removed.
One of the reasons why I kept this batch of kale in place for so long, as well as the
adjacent batch of rocket, is that they served as an excellent host crop for a population
of ladybirds or ladybugs.
I hadn’t considered the possibility of this beneficial aspect of cover crops before.
The ladybird larvae were attracted to the aphids on the kale and rocket leaves, and
then the larva attached to the leaves when they entered their pupating stage, and emerged
a week or so later as adult ladybirds.
Thankfully the timing of this lifecycle more or less matched the timing of the kale and
rocket cover crops, but I probably would have removed them a bit earlier, to give space
for the squash plants, if these beneficial insects were not involved.
But now, the polytunnel is full of ladybirds which will do a great job at keeping the aphid
population under control for the rest of the summer.
So, growing crops in this way has definite advantages, not least of which is the 66kg
of salad leaves that I was able to harvest from these crops, which is a lot, especially
considering that even 100g of salad leaves is quite a bit.
If I don’t count the two batches of spinach which were sown quite late, the remaining
8 batches produced on average of about 3.75kg per square meter of bed, or about 3/4 lb/sqft,
which is quite good, especially if you consider that this is just an infill crop.
But who knows how much would have been produced if I’d grown crops in a more conventional
way in these patches of the polytunnel.
And the hybrid cover crop approach allowed a lot more organic matter to be generated
for my compost pile or for my hens, although I didn’t keep track of the quantities, and
I can only imagine that the soil in these beds is now better off than if I’d left
them empty for that period of time.
Some of these crops were also an excellent host for beneficial insects, but they were
also host to a growing population of slugs, and thankfully I was able to remove most of
these slugs from the polytunnel when I removed the remains of the plants, which ended up
being an added treat for my hens.
So in a way these plants were both a host and a trap crop.
Looking to the future, there is a number of interrelated issues that I'm keen to explore,
such as what is the appropriate density of seeds to sow?
And is there a difference between sowing in drills or broadcast sowing, and when is it
most appropriate to thin the seedlings, and by how much?
Is it better to pick individual leaves, or to use a cut and come again method to harvest
the entire bed?
And, if I notice too many weeds are growing among the seedlings, is it better to just
treat the entire bed as a cover crop, and to not worry about harvesting anything?
Would it be better to dig the plants into the soil, or to use a 'chop and drop' method
and to let them decompose on the surface a bit before I transplanted or sowed the next crop?
Or is it better to wait until the last minute and to pull the plants out completely, to remove them
from the polytunnel, or is it better to let the two crops grow side by side for a while?
How do the issues of crop rotation relate to these fast growing crops, especially with
the brassica family plants.
And what are the possibilities and issues of using the same approach in the outside
gardens, or in the autumn or over winter?
So far, annual spinach is my favourite crop to grow using this method, as it grows really
quickly, is highly productive and high value, it’s versatile in the kitchen, and it’s
easy to freeze any surplus.
It's also neutral from a crop rotation standpoint, and produces a huge abundance of tender biomass
when it flowers, and it’s easy to pull up and chop into the soil, and it seems to leave
the soil in great condition for the next crop.
But, I'm keen to follow Steve Solomons suggestion and to sow regular garden peas, where I can
harvest a few pea shoots at the beginning of the season and possibly some pods as well,
if the crop is in the ground that long.
I wonder if I'll I ever get to the point where I really prioritise the cover crop aspect
of this, rather than seeking to harvest as much as possible, but with so many of neighbours
interested in eating whatever I can grow, I don’t think I’m at that capacity yet.
I am starting to appreciate the benefits that can come with growing certain crops, that
just because I sow them, it doesn’t mean that I have to harvest as much as I can out of them.
And I'm beginning to appreciate more the benefits of always having something growing in the
soil, so long as it can be easily removed when the bed is needed, and if I can get something
tasty to eat out of it, all the better.