Growing Salad as a Cover Crop

Growing Salad as a Cover Crop


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.