Polytunnels and Four-Season Food Production

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It is better to have loved and lost, than never to have loved at all. So, the Tennyson saying goes. I am not sure if he was thinking of greenhouses when he wrote that line, but I can assure you it is true. Many years ago, I was somewhat spoilt by the possession of a double greenhouse and sufficient land to put it on. Not only that, but adjacent vegetable plots and an orchard. And now, sadly, space does not allow for such extravagances. I must admit, for quite a while this left me somewhat bereft over the whole thing, and even wistfully clicking over online suppliers of… dare I say it… polycarbonate sheet!

 

ethereal image of the inside of a greenhouse while soft sunlight shimmers through the roof

More recently, I had a bit of an epiphany over the whole affair, and realised plant cover (as with love) comes in all shapes and sizes. In my crestfallen state, I had failed to heed the permaculture principles “Creatively use and respond to change” and “Use small and slow solutions”. Not everyone can enjoy the good life up in Double Greenhouse Mansions. And the human species made it this far without them. I started this blog with a quote, and if you will permit me, I will further quote Ernst Friedrich Schumacher; Small is beautiful!

To summarise the benefits of polytunnel cultivation:

 

Function and Explanation of Polytunnels

 

Function

 

Explanation

Cultivating Hot Weather Crops

Tomatoes, Aubergines and Cucumbers are happier, with higher yields, than their outdoor counterparts.

Extending Growing Season

Polytunnels can extend the spring growing period by 6 weeks and the winter season by a further 4 weeks. So, vegetables with a long growing season will benefit from being housed in a polytunnel. With skill and planning, unheated polytunnels can be productive over four full seasons of the year in the UK.

Overwintering

In addition to acting as a refuge for pot plants and frost vulnerable species, a polytunnel can store and protect certain established vegetables as though in a larder.

Propagation

The protected environment of a polytunnel is ideal for propagating plants that need a strong start, or by acting as a potting shed early on in the year.

Avoiding the “Hungry Gap”

The period between spring to midsummer was always traditionally a lean period in the agricultural calendar, because outdoor crops were still maturing and the winter stores were dwindling. A polytunnel plugs that gap wonderfully. 

 

I was reading Eliot Coleman’s book The Winter Harvest Handbook when my epiphany struck me. He recommends;

1.Growing cold season crops in winter (i.e. growing cold hardy vegetables). Vegetables such as arugula, beet greens, turnips, sorrel, spinach, leeks, lettuce, etc.  Such plants are naturally cold tolerant and contribute to a seasonally varied diet.

2.Growing plants under TWO layers of cover. Using more layers confers more insulation to crops (protected cultivation). Horticultural fleece, polythene and wire structures, and even hay can become a heat storage medium.

3.Succession Planting (sowing more than once per year). Planting are sown in late summer and in autumn, and are allowed to mature before being harvested. This is the reverse of the typical agro- horticultural concept that plants grow with the waxing solar year and must be harvested before senescence. Succession Planting (in fact the traditional method before the days of refrigeration and mass transport) is used to cultivate plants as they decelerate in growth during the waning solar year.

Polytunnel in October with some Protected Cultivation (Image source: Laila Noort from Sowandso)

When Eliot Coleman mentioned the use of two layers of insulation, it occurred to me that

ALL PLANT COVER IS ONE

By that, I mean it is doing the same thing whether it is a Bell jar, or a football field- sized agricultural greenhouse. Clotches, lean- to’s, cages, mini greenhouses, plastic tunnels, polypropelene, or glass. And with that simple realisation, I was free from the clotches of the greenhouse (See what I did there?).

ADL deliver terrific courses in agriculture, horticulture, permaculture and all things green. Free your mind and your garden: sign up today!

References

Coleman, Eliot. The Winter Harvest Handbook. Chelsea Green Publishing, 2009.

McKee, A and Gatter, M. The Polytunnel Handbook. Green Books, 2009.

McKee, A and Gatter, M. How To Grow Food In Your Polytunnel All Year Round. Green Books, 2010

 

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