A polytunnel in the schools’ garden at Cambridge Botanic Garden, in 2009

It’s at this time of year, I think, that a polytunnel or greenhouse really comes in handy in the garden. Over the summer it may just be a tangle of tomato vines – productive, but a space that you really only go in to keep up with the watering chore, or to harvest ripe tomatoes. You know you’re going to come out with green stains on your clothes and hands that smell funny – tomatoes are like that. Those tomatoes will hang on longer into the autumn than you thought they would, and by the time you’ve cleared out the polytunnel the season will be so far advanced that it will be cold and dark and your crop of overwintering salads will barely be growing – just marking time until the days are long enough for them to actually grow.

So… the time to have fun in your polytunnel is in the spring. It lets you sow seeds, away from the predations of mice, and the vagaries of the weather. You can pop out into the garden and do some serious gardening – without the need to actually experience spring weather. Which, as we know, can leave a lot to be desired. Whilst the sun might be shining, and any great exertion will result in the removal of a jumper, standing still with wet hands is just asking for frostbite.

In the old garden, I had a huge greenhouse – a geodesic Grow Dome, 15 ft in diameter. Although I tried, I never really got the best use out of it, and in the summer it tended to be a desert. There’s space in my new garden for a small greenhouse. I’ve ummed and ahhed about whether I actually need one, given that I don’t intend to heat it over the winter and so it won’t be of any use for overwintering anything tender. Also, I’m not a big fan of tomatoes (could you tell?) and so I won’t be filling it with those. I do like peppers, though. Peppers are good.

Tomatoes and peppers
A polytunnel filled with tomatoes and peppers, at Victoriana Nursery Gardens

Rather than practicing fantasy gardening, it might be worth taking a few minutes to think about the benefits of having a greenhouse or a polytunnel in the garden – they are large structures, and a considerable investment. They are the top level of crop protection, the idea being that they allow us to control the environment inside for the benefit of the plants. They keep out wind, which can be physically damaging to plants, via wind rock, but which also means they need more water, as they lose more to transpiration. Some air movement is beneficial, however. Plants grown in completely still air grow weak and spindly. And ventilation is crucial for another reason – making sure plants have access to the carbon dioxide they need. In a nice, light, warm greenhouse, carbon dioxide can easily become the limiting factor in plant growth, unless there’s adequate ventilation.

Greenhouses and polytunnels keep the rain off – great for the gardener, and also nice for plants that don’t like being wet all the time. It does mean you have to water inside at regular intervals, however, unless you install one of those fancy automatic watering systems.

And they trap heat inside (it’s literally called the Greenhouse Effect, although they could also call it the Car on a Sunny Day effect), which means if there’s any sun at all then it’s warmer inside than outside.

So those seeds on the staging benefit from being nice and warm, and protected from the weather, and the rodents. They can grow on in peace until they’re big enough to be hardened off and moved outside, or transplanted into grow bags to live out their fruitful lives inside.

A variety of plants growing in a large polytunnel at the Centre for Alternative Energy

The result is a longer growing season. We can start seeds, and nurture plants, of species that need a longer growing season than we can count on in the UK. Tomatoes are a good example – marginal in a poor summer, they have a better chance with some protection (which can also be the difference between them suffering from blight, and not). Exotic crops such as aubergines, peppers, melons, okra and sweet potatoes are all from hotter climates than ours, and tend to be more successful inside, unless you have a very sunny and sheltered patio. A greenhouse or a polytunnel allows you to fool plants into thinking we live in a Mediterranean climate – but only for the summer!

So we have a larger range of plants we can choose from. We can also grow some of the hardier things more easily and for longer. Hardy salads will start into growth earlier in the year in the greenhouse, and last longer into the autumn. Even those that are fully winter hardy will be more tender (and cleaner!) when they’re not subjected to the worst of the weather. And often it’s not the cold that kills plants in winter, but being waterlogged or even short of water (if the ground has frozen solid), and indoor cropping allows us to make sure that doesn’t happen.

Birds don’t tend to be a problem indoors, and weeds are easier to control. Some pests and diseases are less of a problem, but others (such as red spider mite and aphids) can be more so.

Hugelmound and polytunnel
A polytunnel edged with a hugelmound. Permaculture in action!

Greenhouses and polytunnels certainly do bring a new dimension to a garden, and it’s nice to be able to potter about with plants and compost, even when it’s raining. I think my ambivalence at the moment is because my garden doesn’t exist yet, not even on paper really. I can’t decide what to grow, and I can’t really imagine what it will be like to be working in the garden, or the greenhouse, and just messing around with my plants. It has been so long since I had the opportunity to do that, that I’ve almost forgotten what it feels like – I just know that I miss it.

How about you – what do you grow in your greenhouse/ polytunnel. And, if you don’t have one, what do you think you would grow if you did?

Disclosure: this post was produced in association with Premier Polytunnels, but the meandering thoughts are my own 🙂

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