Tomatoes are probably the vegetable plant in the gardens that I control the most.
And I generally use fairly conventional methods of stinging these plants up,
and removing all of the side shoots, in order to try to reduce the overcrowding
and to let in more sunlight and airflow, and to try to encourage the plants to
concentrate on producing more fruit rather than more leaves and stems.
The single vines I leave on some varieties still manage to outgrow the height of the polytunnel
space, and I have used several different methods to manage these long plants in the past,
but other plants seem to be a lot less vigorous. And I have wanted to explore a few different
options for managing the growth of tomato plants, including letting some of the side shoots grow.
So this year I tried out 5 different methods with a big crop of tomato plants in my new polytunnel,
to see how they compare in terms of growth and productivity, and the amount of work that
they take, and I am beginning to rethink the strategies that I use for growing this crop.
This past year I grew 140 tomato plants taking up three full beds of the newly established
polytunnel, with 14 different varieties. This was the first time that I have separated
out different varieties depending on the size of tomatoes and how vigorous the plants grew, and it
was the first time that I have used more than one method of managing and pruning the plants.
In one bed I grew 4 tomato varieties that produce large or cooking tomatoes,
on plants that I have found in previous variety trials to be reasonably vigorous
and I wanted to explore growing in ways to encourage greater productivity in a
shorter season. In another bed I
grew 5 medium and beefsteak size tomato varieties, all of which I have found to be shorter plants, or
at least less vigorous than the others. And the third middle bed was planted with
5 varieties of small to medium sized tomatoes, on plants that I have found to be very vigorous,
or at least ones that seem to keep growing throughout the season.
I divided this third bed into 5 different sections, with each section containing all
the different varieties, but with the plants pruned in a five different ways.
Unfortunately this experiment was hampered by poor fertility later in the season.
This was a newly established polytunnel, and despite the abundance of compost and concentrated
fertility that I spread over the soil, the tomato plants didn’t grow well later in the season, and I
didn’t correct the apparent lack of fertility. And I wasn’t so great at keeping up with the
regular tasks of pruning and removing all of the side shoots, which would have affected
the growth of the plants and the ability to properly compare the different methods.
So this was not a great controlled exploration, but we were still able
to harvest a huge amount of tomatoes out of this polytunnel, and I learned quite a
bit about the differences between the various methods of controlling and guiding the plants.
The method I have used the most in the past involved removing all of the side shoots that
formed on all of the plants, removing lower leaves as they started to get too old, and to
wind the one leader or growing tip up a length of twine hung from the polytunnel structure.
And when the plant reached the top of the polytunnel,
I untied or unhooked it, let out some more twine and hung it further down the wire,
allowing the lower part of the vine to trail along the surface of the soil.
And I would repeat this process as necessary, and looping around to the other side of the bed,
allowing more of the vine to form a long loop on the surface of the soil.
And the plants could keep growing for the full length of the season, some of them growing over 5m
in length, in polytunnels only 2 to 3 meters tall. But dropping the plant in this way often meant
that the fruit that was still ripening on the lower trusses were often laying directly on
the soil, caused some tomatoes to rot, and made it more difficult to harvest the rest.
I used this fairly common dropping method with one of the sets of the more vigorous
varieties of tomatoes in the middle bed, and because of the higher height of this
new polytunnel compared to the older one, fewer of the ripening tomatoes ended up touching the soil.
A few years ago I started to adapt this method of dropping a single vine of tomatoes,
to try to support the lower parts of the plants rather than having them trail on the ground.
When the plants reached the top of the polytunnel, I tied a second length of twine to the stem at
about waist height, and rehung it so that the bottom part of the plant was more vertical, the
middle part was more horizontal and the growing top of the plant was sloped more vertically again.
And whenever the more horizontal part of the middle of the vine crossed the secondary
support twine for the adjacent plants, I would add another clip to support it,
and as the plants grew they would form a type of woven basket hung off the ground.
With the same kind of pruning of the older leaves, and removing all of the side shoots,
the trusses of the tomatoes would hang below the vines, but up off of the soil,
which made them a lot easier to harvest.
But it was also the method that required the most amount of work, with a lot of
tying and rehanging and additional clipping that wasn’t need with the dropping method.
I used this hung basket method on another set of the more vigorous tomato varieties growing in the
middle bed, but the results from these plants as well as form the plants that were simply dropped,
would have benefited from a longer growing season if I had managed to adequately feed the plants.
Another possibility for managing these plants is to simply cut off the growing tip of the single
stem when it reached the top of the polytunnel, to try to encourage the plants to focus on ripening
the existing fruit, rather than continuing to grow more flower trusses as well as leaves and vines.
I tried this with some of the larger fruited varieties, where I pruned off the one growing
leader when it reached the top of the twine, and continued to prune off all of the side shoots that
developed as well as the older lower leaves. And I also tried this heavy pruning method
with one set of the more vigorous plants, to see how this method would work with
plants that I would normally allow to grow for much longer in the season.
I had also planted these plants in this set at a much closer spacing of 25cm apart, fitting 12
plants staggered along a 3m length of bed, which is considerably closer than the 40cm spacing
that I typically use down the centre of the bed. I was thinking that this higher density of plants,
with the one leader cut off when it reached the top of the polytunnel, would produce a larger crop
in the same area in a shorter season, even if the total amount harvested from the plant was less.
I had heard that leaving even one of the side shoots to grow would help to reduce
the vigour or height of the tomato plants, as well as increasing the total amount that
could be harvested from each plant. I decided to try this out with the
full bed of 5 varieties that produced medium or beefsteak size tomatoes.
I left a really strong side shoot a bit higher up on the plant to grow as a second stem,
and I wound the two leaders up separate lengths of twine attached to the same overhead wire,
and pruned any growing tips when they reached the top of the polytunnel.
And this method was very useful for two of the varieties that seem to naturally focus a lot
more on producing fruit, with surprisingly little foliage, and not a lot of side shoots to remove,
producing a really heavy crop with not a lot of work to manage the plants.
I also used this fourth method on another set of the vigorous varieties,
pruning them to two strong vines, which were hung from two separate wires so that the
plants pulled out from the centre of the bed. This opened up the plants a bit more which
made it easier to harvest, and let more light into the centre, and all of the growing tips
of these vigorous plants were cut when they reached the top of the polytunnel.
I had expected these plants with two stems to be slower growing, or shorter than the same
varieties with single leader, but any difference wasn’t that noticeable, which I find interesting.
With the last of the 5 sets of vigorous plants in the middle bed I decided to let
the plants grow with multiple vines, as I had read that this was a useful strategy if each of
the plants had enough space for the extra stems. I planted one plant of each variety 60cm apart,
and let some of the stronger shoots continue to develop.
And I found this a bit more difficult and time consuming to manage, partially
because I was not attending to the pruning frequently enough, but these plants seemed
to produce more growth to remove, with more stems producing more side shoots.
I ended up with 5 or 6 vines or stems on each plant, growing up separate twines
tied to the overhead wires, and more frequent attention and pruning would
have helped these plants even more than the other methods.
These plants seemed to produce fewer tomatoes earlier in the seasons, and the growing tips
reached the top of the polytunnel not long after the plants that were more heavily pruned.
I think these plants needed even more space to grow into, or I should have left fewer vines,
and I am not sure wether the limited impact on the height or vigour of
the plants was worth the extra work. But perhaps this strategy of leaving
multiple shoots to grow would be more successful on a less vigorous variety, or when I wanted
to get the most out of really expensive seeds or a limited number of transplants.
Looking at the average weight of the tomatoes harvested from the plants in each set,
the plants with multiple stems produced a lot more per plant, and the ones that were heavily
pruned were definitely lower yielding. And I do find it interesting that the
two sets that did not have the top of the plants cut off did not produce as much.
I think they were most affected by the premature end of the season, as these plants would have
put in more resources earlier in the year to continue growing more leaves and flower
trusses that were not able to produce fruit. And this is very apparent when looking at
the yield of kilograms per square meter for each set, where these two methods produced a lot less.
I assume that these plants would have been able to produced a lot more if they had been able to
grow a lot longer, more so than with the plants pruned in other ways, and I suspect that these
methods would be able to accommodate a higher density of plants, more plants in the same area.
The densely spaced plants that were most pruned or controlled produced
a higher yield than the plants with double and multiple stems.
So there is a difference in terms of overall yield per square meter of bed,
but not so much, despite the significant difference in the density of the plants.
But looking at when the tomatoes were harvested, the higher density of more heavily pruned plants
produced a greater yield earlier in the season. The double stem plants were less, and the dropped
and hung plants producing substantially less, but they all followed a fairly similar curve.
But the plants with multiple stems seemed to be quite different, producing a lot less earlier on,
but then rapidly catching up in the second half of the season.
It seems that these plants were devoting a lot more resources to
growing more leaves and stems earlier on, that only really started to produce later.
After this year’s explorations, if had to pick one method to use on all tomato plants,
I would probably let two stems develop on each plant and then cut off the leaders
when they get to the top of the polytunnel. But it would be good to repeat this type of
side by side trial, especially to get a better understanding of how the vigorous varieties
would produce if they were allowed to grow for longer, and fed for most of the season.
I do like the idea of getting tomato plants to produce for as long as possible,
to extend the season of this popular vegetable, and I hesitate to remove crops when there are
still green fruit that might be able to ripen. But perhaps I need to think differently about
all of this, and focus on getting a big crop with less work, from a shorter season, which seems to
be possible with plants that are pruned hard to a single or double stem, with the tops cut
off when they reach the top of the polytunnel. This could be less work, but probably produce
fewer tomatoes overall, and it the plants would be encouraged to put the energy into
ripening the existing fruit earlier, so the plants could be removed, so that the space
could be made available for another crop. But this might not make as much sense in
the smaller or shorter polytunnel, where there just might not be enough height to
get the decent crop, and dropping them a few times may actually be better.
And if I wanted to harvest tomatoes later in the season, perhaps it is better to plant
different batches at different times, to be able to staggered the harvest, with only
some of the plants producing into the autumn. And this would allow other spring crops to grow
for longer, rather than clearing everything and planting all of the tomato plants at the
same time early in the season, and allow earlier crops to get into the polytunnel in the autumn.
With the temperate maritime climate that we have here in Ireland, tomatoes plants will probably
always be a heavily controlled and pruned crop, and one of my favourite vegetables,
but perhaps it is not a crop that I need to try to grow for as long as possible.