Lettuce is a very popular crop and it's one of those crops that I would like to produce
lots of all year round but we haven't quite got there yet. The low light levels that we
get over winter really slow down the growth of many plants and there are other salad greens
that grow much better than lettuce at that time of year. The relatively cool summers that we
get here in Ireland usually create quite favourable conditions for growing lettuce
through the summer and into the autumn, though I'm often distracted by the abundance of other
crops we can grow at that time. But it tends to be in the spring and early summer that we
are most successful at growing an abundance of lettuce and the most consistently successful
harvest usually comes from overwintering plants in the polytunnel that we harvest as
lettuce trees. And this year we were even able to save seeds from the same plants.
I have been trying a few different ways to grow lettuce, each of which can be useful at different
times of the year and in different contexts. We grow crops in a very conventional way to
harvest as full heads of mature or semi-mature lettuce, and this is possibly the easiest way
to grow and harvest lettuce. But with this type of production there is a longer period
of time from sowing until harvesting, and there can be a glut when all of the lettuce heads are
ready to harvest within a fairly short period of time. We generally try to sow small batches quite
frequently in order to maintain a reasonably consistent supply, and I like to include a
few different types of lettuce with a sowing like this which can help spread out the harvest a bit,
as not all of the types mature at the same time. This also provides a certain amount of diversity,
but if we are only harvesting a single head of lettuce at a time, then we only have that variety
of lettuce to eat that day. The other common way that we grow lettuce is as a cut-and-come-again
crop, which can provide a wider mix of leaf types for harvesting all at once, if we sow a mix of
different varieties in the same space. We can also harvest a first cutting significantly earlier than
when growing full heads, and can adjust spacing of seeds depending on the size of leaves that we want
to harvest. I find that we can generally get two or three cuttings of good quality leaves out of
a crop like this, and it is possible to harvest the whole batch, or only cut as much as we need
for that day. I've also tried a variation of this method where I use a process of selective thinning
whole lettuce plants in order to harvest them. I start by sowing the seeds quite close together,
and then cutting out some of the small plants to eat as baby leaves and give the the plants
space to grow into. And then we continue to thin the plants whenever we want lettuce,
but making sure to remove plants fast enough so that there's enough space for all of the
remaining plants to grow without getting too crowded or stressed. This harvest-thinning can
keep going until the plants are spaced wide enough apart for full size heads of lettuce to develop,
which can be harvested when they're ready. If we manage to keep on top of the thinnings we
can harvest from this single sowing over a much longer period of time. Or we can harvest the
entire crop at any time if we need the space for another crop. And the fourth method I've
tried is to only harvest the outer leaves off of fairly widely spaced plants, leaving the plants to
grow from the undisturbed inner leaves. I first learned about this method from Charles Dowding,
and I find it to be quite a successful and easy to manage way to grow lettuce.
This process of only harvesting the outer older leaves of a plant and leaving the younger smaller
leaves to mature some more, is common with other crops especially chard. This method of harvesting
lettuce seems to becoming more common, and as the harvests continue the single stem of the
lettuce plant tends to become bare and quite tall leaving a cluster of smaller leaves at the top,
similar to a palm tree which is why I call them lettuce trees. I have been growing lettuce in
this way for about five or six years, mostly in the polytunnel and I tend to use varieties that
have a more open habit, like a loose leaf lettuce, and avoid the varieties that tend to close in on
themselves to form a solid head. I generally space the plants far enough apart in the bed
so that the semi-mature leaves of adjacent plants will just touch each other, effectively closing
the canopy and sheltering the soil on the bed. And I try to delay the first harvest until the
leaves are quite big, letting the plants become quite established first. I'm still
not sure if there is an ideal amount of how many leaves to harvest from each plant at each time,
as I think there are so many different factors, and for me it generally depends on how much
lettuce we need at any one time. Picking only a few leaves at any one time means that there are
more leaves left on the center of the plant, so that there's theoretically more photosynthesis,
and the plants can potentially grow faster, and the plants will be ready for harvesting
again sooner. Picking a lot of leaves at once and leaving only a cluster of a few small leaves at
the top of the plant, means that it'll be longer before the leaves are ready to harvest again,
but I can get a bigger harvest at any one time. This all depends on our need and the time of year
and how many your plants we are growing, but I like to have a stock of lettuce available for
harvesting whenever needed so I tend to pick only a few leaves from any one plant at any
time. Either way I found that the harvest can last quite a long time in the season.
And as we continue to harvest the space on the stem between each leaves begins to get bigger,
which is a sign that the harvest is coming to an end. And I usually keep harvesting until
the flower bud forms in the top of the plant, or the leaves become bitter and don't taste as good,
often because the polytunnel is getting too warm, or when I simply need the bed for another crop.
Most of my experience with growing and harvesting lettuce like this is in the polytunnel in the
spring and early summer, usually from plants that I sow in the early spring. This year I had really
good harvest from plants that had overwintered in the polytunnel which were originally sewn into
soil blocks in October last year. I transplanted 52 plants into the bed in early December, after
the summer crops had finally been cleared, but I only grew two varieties this year,
a red and a green salad bowl, both of which I found produce really well when harvested using
this method. I spaced the transplants 25 cm apart both directions, and as they started quite small,
and with a slow growth over the winter, the bed seemed quite empty for quite a while. We
have fairly mild winters here in Ireland, but not a lot of sunlight, so there's not a lot of growth
but all of the plants survived, and were able to become established for quite rapid growth once the
sunlight and warmth increased in the spring. And by the third week of February we started
harvesting a bit from these plants, which was probably a little bit early, but we were hungry
for fresh salad greens. For the first while we were only able to harvest less than a kilogram
of lettuce from this full bed each week. But by the end of March the rate of growth had increased
dramatically. Harvesting every few days we were able to get over 2 kg of lettuce each week,
which is a lot of lettuce, and this peaked towards the end of April at almost 4 kg a
week from this large bed. And the amount that we could harvest trailed off quite dramatically in
the beginning of May, as the plants diverted most of their energy into developing the seed heads.
And the leaves didn't taste very good with this process and the developing heat in the polytunnel.
In total we harvested 25 kg of lettuce from these 52 plants, and had a lot of lettuce to
share with neighbors this spring. That works out at just under half a kilogram per plant,
and I don't know how it really compares to growing the same varieties and harvesting
them as full heavy heads, but that seems like a lot of lettuce per plant. And this translates
to almost 8 kg of lettuce per square meter of bed, which is a really good yield for any crop,
especially for a high value crop like lettuce, for only part of the season. This is definitely
a lot more than I've been able to harvest out of a crop of closely spaced lettuce plants which we
harvested using a cut-and-come-again method, and the wide spacing and method of harvesting seems
to allow the plants to last much longer from this batch of plants. This year we were able
to harvest over a 12 week period, which is quite a long time, from the latter part of February to the
beginning of May. But I think it would have been better to have delayed the initial harvesting for
a few weeks, to allow the plants to become even more established, before we started to remove the
older leaves. This extended period of harvesting is definitely one of the benefits of this method
of growing and harvesting lettuce. And I also like the flexibility of how much we can harvest at
any one time, either harvesting a lot and almost stripping the plants, or leaving more to harvest
again soon sooner. But we can do the same with other methods. It's also nice to have a diversity
of different types that we can harvest at any one time, to be able to pick and choose between the
different varieties, even though we only grew two varieties in this last batch. I also think it's
really useful to remove the older leaves before they are in contact with the soil for too long,
so that they don't start to deca, and we end up eating most of the leaves that are produced.
And clearing these leaves also leaves a space underneath the plants that can be clean and dry,
and very few places for slugs to hide. This regular harvesting and removing the older
leaves not only cleans up the plant and encourages them to put the resources into the newer leaves,
it also makes it easier to do some weeding and to keep an eye on the plants on a regular basis.
But the appropriateness of this method really depends on what I want. If I wanted to harvest
lettuce leaves really small then it's probably better to fill a bed full of lots of closely
spaced plants and to use a cut-and-come-again method. And other varieties of lettuce are much
better as a fully formed heads, such as cost lettuce. And I really don't know if this method
of harvesting the outer leaves of widely spaced plants is really that useful during the summer,
or other times of the year outside, and this is something that I want to explore.
An unexpected benefit of this method of harvesting lettuce is to be able to save seeds from the same
plants that I was harvesting from. I usually save seeds from vegetable plants that are growing for
the specific purpose, in a separate area to keep them away from the general crop rotation of the
gardens, except for crops like peas beans and tomatoes. I have saved lettuce seeds in the past
growing a number of plants in a dedicated space, and was able to save a lot of seed from them. But
as the plants of the batch of lettuce trees that we growing this spring were starting to bolt,
I decided to leave a cluster of plants from each variety to continue to develop seeds, and to clear
the rest of the plants. Apparently it's okay to save lettuce seeds from different varieties that
are spaces close together, but I wasn't sure if these plants that had had so many leaves harvested
had been able to build up enough reserves of energy and nutrients to be able to produce a lot
of strong seed. But these plants produced a lot of very tall flower stocks, and I ended up removing a
few of them in order to reduce the overcrowding, and I needed to use some twine and canes to keep
everything upright. These plants produced a lot of flowers, which developed into a lot of seed heads,
and by about the third week of July, or about 10 weeks after the final harvest of leaves,
I cut off all of the seed stocks and removed them. This was probably too early for some of
the seeds to develop, but I needed to make space for the quickly growing squash, corn and beans
that I planted around them. I ended up with over 100 gram of seeds from each of these varieties,
which is more than enough to grow for many years, especially if I store them in the freezer,
and plenty to share with many other growers. I hadn't planned on saving seeds but it ended up
being an added bonus from plants that I had already harvested so much from,
something that I wouldn't have been able to do with most other ways of growing lettuce.
I’ve already sown some of these seeds, which have produced really healthy seedlings,
which I'm about to transplant underneath the tomato plants in one of the other polytunnels.
There is already another batch of lettuce that is inter-cropped on the other side of the bed,
which are almost getting to the point where I can start to harvest. The tomato plants growing
above are heavily pruned at the base so they're letting in a fair amount of light, but still
providing a certain amount of shade for those hot days that we are still getting. I planted
one lettuce plant at the location of each drip along the drip line pipes which will definitely
help with the watering. But this produces a bed with plants based farther apart than I would
normally grow them, especially once the tomato plants are removed. But I'm hoping to be able
to harvest a lot from these plants over a long period of time using the lettuce trees method.
It will be interesting to see how these lettuce plants develop as the weather gets cooler and
the days get shorter, but I don't really know how lettuce plants respond to the changing seasons,
so I don't know when these plants will start to produce a flower head. It will be interesting
to see if they will produce over the full winter, and possibly even into the spring,
and how much can be harvested. We have also been growing a lot more lettuce as part of the quick
rotation crop beds that we have established this year as a cut-and-come-again method,
with smaller batches and a faster turnover, that is part of the strategy for managing
this area. But when plants can grow in a bed for much longer, especially if they can grow
over winter in a polytunnel, or some other form of protection, then I think growing them
and harvesting them as lettuce trees is a good option. I have found that this method can produce
a lot of lettuce for harvesting in the spring and early summer, before the beds are needed for the
main warm season crops, and before crops in the outside gardens have really started to produce.