A polytunnel or a greenhouse is a great place to grow heat loving crops, especially in the cool
maritime climate that we have here in Ireland. And a lot of these vegetables that I want to grow are
vining plants such as cucumbers and beans, that have a natural tendency to climb up any support
that is available, either by winding up things or sending out tendrils to grab on to things
for support. Others are more what I would call scrambling plants, like tomatoes plants that
will grow up and over anything and can spread out over a wide area, but don’t have the same natural
ability to grip on to anything. Although it is possible to simply let these plants grow along
the surface of the soil without any support, they will easily take over a space that's available
and make it very difficult to move around the polytunnel. So, like many growers I put in the
effort to control these plants, and provide support to help them to grow vertically. This
allows me to grow a lot more plants in the same area, and increases the yield, and it also makes
it easier to be able to move through the space, to maintain the plants and harvest when needed. But
this does come at the cost of more work throughout the season, and it also means that these plants
typically reach the top of the support and bump up against the polytunnel plastic mid way
through the season. In order to deal with all of this I have developed several strategies for
managing the growth of these tall plants in the relatively short space of one of my polytunnels.
Climbing French Beans are among the easiest vegetable plants to get to climb, and I like
to grow them in the polytunnel as they are a quite high value crop, and are also quite productive. I
grow them up a length of twine that has one end tied to a stick or stone that I bury in the soil,
and the other end tied to a support wire hung from the polytunnel structure. Once the leaders find
the twine, they grow up it very quickly, typically reaching the top of the 2m high space of the
polytunnel within 7 or 8 weeks after sowing, and before any of the beans are ready to harvest. At
this point I try to make sure that some of the leaders are looped over the top wire so that the
weight of the plants is supported properly , and I then simply let the leaders hang down as they
continue to grow. But the plants also send out a lot of side shoots, and they can really get quite
bushy, but I typically just leave them alone apart from making sure that vines don’t spread
out to interfere with the other crops. I have noticed that the first crop of the beans form
on the oldest part of the vines that are growing upwards, but if I manage to harvest most of them,
then the plants typically try to produce a second flush of beans later in the season. But
this second crop of beans seems to grow on the newer parts of the vines that are hanging down
from the top of the support. This season I didn’t sow the plants easily enough to allow
enough time to be able to harvest anything from this second flush of beans before the
temperatures dropped in the autumn. So I wonder if it would have been better to prune the tops
of the vines as they reached the polytunnel plastic, rather than let them continue to grow.
I also grow the cucumber plants up a length of twine But unlike the french beans,
the cucumber plants need help climbing up the support even though they send out tendrils to
grab onto anything, and it is a relatively regular task throughout the season to wind the tip of
each plant up around the length of twine. And followed the advice of other growers, I also
prune the plants heavily to control their growth by removing all side shoots so that there is only
one growing point at the main stem, and in some cases reducing the number of fruit that develop. I
used to cut off the growing tip of the plant when it hit the top of the polytunnel but recently
I have taken inspiration from other growers and now let the plant grow over the support
wire and down the other side. The vines need some encouragement to hang down rather than climb back
up, but eventually their own weight takes over. I also prune a lot of the older leaves as the plants
grow, and have done this more aggressively this season, but I'm still not sure how much and how
frequently is most effective but the more I do it the less shading of the new hanging growth there
will be. A few of the vines have grown right down to the ground, so the plants are twice as long
as the 2m height of the polytunnel, and they can start winding up the original vine again. Now
that I know I can keep the plants growing like this, I am interested in sowing the
cucumber plants earlier in the spring, in order to possibly get a bigger crop
over a longer part of the season, if I can keep the plants healthy and happy.
Tomatoes are also heavily controlled plants in my polytunnel, and similar to cucumbers, I regularly
prune all of the side shoots, and leave only one growing tip at the top of the main stem. This
growing tip is regularly wound around a length of support twine, a task that is relatively easy
if done quite frequently. With such short season here in Ireland, I suspect I could simply prune
the top leader of the plants when hits the top of the polytunnel, to end the growth of the plants
and encourage them to focus on ripening the tomatoes of the existing trusses. But
I usually try to push these plants, allowing them to grow for longer in
hopes that I can get more tomatoes, but this takes effort. I usually sow the plants early
in the season and so that they tend to be quite tall by the time I get them into the garden bed,
and in the past I have planted them quite deeply, gaining an extra 15-20cm of growing space before
they reach the top of the polytunnel. But this season With the crop of tomato plants in my
smaller polytunnel I dug a trench down the middle of the bed which I amended with extra fertility
and I laid the plants on their side with only top few leaves sticking out above the soil level. With
this method I buried about 30-40cm of the stem without having to dig too deeply,
and the plants had more space to grow before hitting the top of the polytunnel. This
also allowed more roots to grow from the buried stem,
and the existing root ball was closer to surface where all of the fertility and compost is.
In order to allow the tomato plants to continue to grow in this short space, I've used a process
in the past where I retie the twine in a way that allows the bottom section of the stem to
lie along the surface of the soil. This year I tried a different method of tying an additional
piece of twine around the stem at about waist height to support the bottom part of the plant.
I then moved the main twine along the support wire and with enough slack so that the middle
part of the plant was able to sag. This created more of a stepping pattern in the plants, with a
horizontal part of the stem under the soil, then a vertical rise above the soil, a more horizontal
section at waist height, before rising again. Dropping the plants like this gave another 60
cm or more of potential growth at the top of the plant, in addition to the 40 cm of buried stem. So
the plants are at least one meter longer than the polytunnel is high, and everything is within easy
reach. I could have continued with this stepping and dropping process but with the season coming to
an end I decided to prune the leader when it reached the polytunnel plastic again,
encouraging the plants concentrate finishing ripening the existing fruit.
Because I also removed a lot of the lower leaves as the plants grew, this meant that most of the
clusters of tomatoes hung down below the leaves where there was lots of light and air movement,
and this made it easier to harvest and the tomatoes were better quality. But
this technique is a fair amount of work and I'm not entirely convinced it is worth the
effort of dropping the plants rather than simply pruning them when hit the top of the polytunnel.
Squash and pumpkins are also quite vigorous vining plants, and are hard to control in a polytunnel,
and I haven’t been impressed with the results that I've been able to get in the past,
probably because I haven't given them enough attention. I tend to grow a
few plants in one of the corners of my smaller polytunnel so that they are easier to contain,
and I have tried tried to stringing up a few of the vines to keep them off ground,
but I've not been very systematic with this task that is made more difficult with the
sloping sides of the polytunnel. Once the space fills up I do prune off any additional vines,
but I suspect that it would be better to try to control and prune these plants a lot more,
and to also give them more space or at least more height to grow into. If I grew a few squash plants
in one of the middle beds of my polytunnel I could take advantage of their natural climbing
ability to grow up a trellis or wire netting that I hung from the polytunnel structure.
Or I could space them much closer together, and prune them really hard to just one leader manage
them much like I do cucumber plants and allow them to wind up one piece of twine, and even if
I only let a couple of squash to ripen on each plant, this may produce a higher yield out of a
smaller space. I may try something like this next yet as to date I haven’t been very pleased with
the results I've had from growing these vigorous plants in the cramped space of the polytunnel.
but the climate tends to be too cool here in Ireland to grow a lot of varieties outside.
All of these different types of plants can be highly productive in the warmer climate of the
polytunnel, but they can also take a lot of work. Finding the right balance between productivity
and effort depends on my priorities, do I want to get a bigger harvest possible or do I want
to reduce the amount of work that I have to put in. As one example, I could reduce the workload
quite substantially with the tomato plants if I simply cut off the leaders when they
hit the top of the polytunnel space, and accept whatever came from the existing flower trusses.
And if the tomato plants are finished earlier in the season, there is more time to get another
crop growing in the same bed, but I still want to grow lots of tomatoes. There is a
balance there somewhere, and there are also a lot of other possibilities and techniques
that may be more appropriate in my context, and I'd love to explore a lot of them in the future.
In general I've found it really useful to learn from the various methods and techniques used by
other growers, and it is great to be able to benefit from their trials and experiences.
But I also need to recognise that they might be working in a different context and climate,
and I might not have the same priorities and constraints that they do.
So I think it's important to explore and compare different methods and techniques myself,
rather than simply accepting that there is best way of doing something.