Polytunnel on the Edge

There are many readers more fortunate than I, who can grow tomatoes outdoors. I love where I live, just a wee hop and skip south from Dunnet Head, the most northerly point of the UK mainland. (Sorry to disappoint those of you who have visited, and believed you had reached the top of Britain, but John o’Groats is not the most northerly point. You’ll have to come back!)

Being so close to the raging Pentland Firth, and with no land mass north west between me and the Arctic Circle, this is a challenging place for a gardener. If I could transport the climate of Kent, and impose it as a micro-climate within the windswept hedges around my garden, I would. But only if I could keep the big skies and empty roads.

Already I hear 98% of you thinking, “So how is this relevant to me?”. Well, it’s the same principle as the one which states: always buy plants raised north of where you will grow them, because they will be hardy and survive.

My experiences in extreme gardening conditions will, I hope, be relevant to those of you on the North Yorkshire Moors, Dartmoor, and many other locations throughout the UK where gardening conditions are less than benign. To those of you in more favourable gardening locations, anything I can do, you can do better. But the basic principles apply.

So what do you do in unfavourable conditions? You get a small polytunnel. In fact, you should get the largest you can afford, although in my case it is quite small. But it was the largest I could afford at the time. Eight feet by twelve in my terms, which is approximately 2.4m x 3.6m for those of you who are too young to understand chains, furlongs and cubits.

Why a polytunnel rather than a glasshouse? Well, apart from the obvious issue of cost, I have seen glasshouses completely destroyed in a storm. Picking up umpteen square metres of glass shards is in itself a situation you want to avoid, never mind the replacement cost. I have also seen aluminium glasshouse frames distorted beyond salvation.

A polytunnel, from a reputable source, has a sturdy tubular structure, and the curved shape deflects wind over it. In fact, the way the wind blows over a polytunnel actually keeps its feet in the ground, by a downward force. I think it is something to do with aerodynamics, but I’m a gardener, not an engineer. Anyway, the structure usually remains intact, no matter how severe the storm. The worst that can happen is a ripped cover.

Covers are relatively cheap to replace, and certainly a better bet than umpteen panes of shattered glass.

The structure is the important part, because while covers come and go, a solid structure is there for life, to be re-covered ad infinitum. In an exposed location, I do believe that a proper heavy-duty cover is worth the extra you will have to pay, and in particular it is worth buying a heavy-duty cover as part of a package. If you are buying a structure, the little bit extra you have to pay for a heavy-duty cover is but a token, compared with the cost of buying the same as a separate item. At least, that is my experience of most sellers.

So hopefully I have convinced you to go for a polytunnel rather than a glasshouse. The next issue is, what to grow in it?

And remember, I’m talking to those of you gardening in less favourable parts of the UK, of which there are many.

Strawberries. Yes, I can grow them very successfully outside, but those early ones are even nicer. Space is limited, so I only have four plants. I dig them up and replace them every three years, and the new runners – saved from the outdoor plants -  are set in a different part of the tunnel. Crop rotation is every bit as important under polythene as it is outdoors, and perhaps even more so.

Courgettes. Perhaps two years out of three I can grow them outside. Wind is the problem. With their sail-like leaves they catch the wind and it twists them until the stem breaks. I always have one courgette in the polytunnel, just in case. It can become a triffid, but you just have to keep cutting leaves off when they threaten to swamp other crops. It does no harm.

Dwarf French beans. I always put four or six in the polytunnel, because the ones outside are less reliable than courgettes. One year out of three, perhaps, I get a successful harvest. Wind again is the main obstacle. The delicate foliage is shredded. One shredding they can maybe recover from, but more than that means their demise.

Tomatoes, obviously. I can’t grow them outside. They occupy more than their fair share of the polytunnel, but that’s fine. And when the glut comes, they are converted to soup and ensconced in the freezer, to be welcomed again in the cold dreich days of winter, as a warming reviver after a foray into the garden in horizontal sleet picking finger-numbingly frosted sprouts.

Grapes. Yes, within this small tunnel I have a grape vine. It is trained along the roof, and pruned viciously to minimise the shade it casts. Actually, the pruning is good for it. It is still young, and hasn’t produced enough grapes yet to make even one bottle of Chateau Caithness, but this year it is looking promising. Watch this space.

Dahlias and Chrysanthemums. Yes, I find room to grow flowers too. Both of these can be grown outside, even here in the far north. But one stormy wind can wreck them. So I find space in the polytunnel for a couple of each, which I can cut and give to friends. And in the polytunnel, neither have to be lifted and overwintered. They are perfectly happy to stay in the soil borders, and spring up again next year. The polytunnel provides two elements of protection for them – protection from

Salads. This has to be the best reason of all for having a polytunnel. Since I got it, I have never been without fresh salad leaves. As soon as the tomatoes are cleared out, late September or October in a good year, I sow lettuce and mixed salad leaves, of the cut-and-come-again variety. They provide me with fresh salad right through the winter, and when the first of the outdoor leaves are ready, they are unceremoniously grubbed up and thrown out. But it is not just conventional leaf salad you can grow over winter in a tunnel. Mizuma, Chinese leaves, Lamb’s Lettuce, Rocket – in fact just about any of the salad crops you would sow in spring and summer, will produce reliably through the bleak months. And so will spring onions and radishes. With a tunnel, you will never be without a salad.

Young Plants. The polytunnel is worth its weight in gold in Spring. I don’t have electricity to it, so I raise seedlings on a basic heat mat on a windowsill. But as soon as I can, I transfer the seedlings to the polytunnel, covering them with fleece if a hard frost is forecast. All my brassicas, leeks and bedding plants follow this route. I would be lost without it. I have erected a windbreak area on the south end of the polytunnel, for hardening off. And that’s an idea I would recommend. All plants raised in artificial conditions need to be hardened off gently. If the hardening-off area is adjacent to the polytunnel, it makes life so much easier.

So let me summarise. My apologies for boring those of you who can grow tomatoes outdoors. My apologies for offending those of you with glasshouses.

I hope, however, that this personal view of my polytunnel and what I do with it, will strike a chord with those who garden in the harsher parts of our country.

Remember, my polytunnel is only eight by twelve, but foot for foot and metre for metre, it is the most productive part of my garden.

© Mike Clark 2007

Published in Organic Gardening October 2007