Love in a cold climate: the solitary secrets of my polytunnel

If someone had told my teenage self that something as unabashedly utilitarian and ungainly as a polytunnel would one day occupy a special place in my affections, I’d have hooted loudly with derision. An object defined as an elongated polythene-covered frame under which seedlings or other plants are grown does not, after all, have the same whiff of glamour as vintage jewellery or designer jeans.

But so it came to be. Now, my middle-aged self relishes the solitary hours spent under its drum-tight, waterproof, transparent plastic ceiling, being part of a parallel but meteorologically benign universe where frost is rare and heavy rain and strong winds can do no harm. Here, I can garden in my own private, solar-heated biodome to the steady, melodic thrum of raindrops without getting soaked. Harvest heat-loving food crops that would otherwise languish in the damp, fungal cool of an Irish growing year. Pick perfumed flowers in bloom months earlier than their garden-grown equivalents. And glory in the tiny wrens and pollinating insects that visit it even in the depths of winter.

It is, as one friend described it to me, a classic case of polytunnel love. And I’m not alone. In a country such as Ireland where the weather is predictably unpredictable, undercover gardening makes so much sense that hordes of gardeners have invested in a tunnel in recent years. It’s a fact confirmed by Deirdre Warren of Colm Warren Polytunnels (CWP), the highly-regarded, Meath-based, family-run business established in 1974. She estimates that during its busiest season (February to June) the firm installs an average of 10 domestic tunnels every week, allowing green-fingered gardeners all over the country to alter the climactic odds so that they’re firmly in our favour.

So what are the dos and don’ts of getting a polytunnel? Let’s start with careful site selection. The ideal is a fertile, free-draining, weed-free soil in a spot that that’s reasonably level and open but not painfully exposed. In other words, far away from the shade and competing root systems of trees/ shrubs/ hedges, but not completely without shelter. In a perfect world, your polytunnel should also be orientated east-west along its length to maximise light but this isn’t always possible. What is of paramount importance is that it gets a great deal of direct sunlight (at least 6-7 hours a day), as much of its internal heat is as a result of the suns ray’s touching its taut plastic skin.

How big?

The perfect size? That all depends. CWP supplies domestic polytunnels as small as 8ft by 10ft (from €1,025 including installation) which are especially popular with allotment holders eager to maximise returns on their annual site rental fee, but its best-selling garden polytunnel is its 14ft by 24ft model (from €1,318 including installation). Dimensions can sometimes be deceiving, however, and Deirdre Warren warns buyers to beware of cheap substitutes.  “Rather than sharply curving supports, all of our Irish-made polytunnels have tall, straight sides that maximise the internal growing space.” The company also prides itself on using only high-tensile galvanised steel for the supports and heavier, tanalised-E treated timber for the door frames, gable ends and ground rails.

Similarly, the strength and quality of the polythene “skin” will affect how quickly your polytunnel stores and disperses heat. Standard CWP polytunnels are covered with an 800-gauge, thermic, anti-drip, clear polythene, but the company can also supply both extra-strong (1,000 gauge) polythene as well as “diffused” polythene to reduce the glare of very bright sunlight.

The basic structure aside, put careful thought into the extras and/or accessories. For example, the edges of your polytunnel’s polythene skin can be “trenched” into the ground (the cheapest option) to secure it, but attaching it to timber or aluminium ground rails will give a tighter, tidier finish and extend the plastic’s natural lifespan (typically 6-8 years after which the polytunnel needs to be recovered). Installing a 60-90cm wide, weed-suppressant membrane around the perimeter of the structure will also help to fend off invasive weeds. The number of doors is another important consideration: for polytunnels longer than 24ft, Deirdre Warren recommends one at either end to help with ventilation.

Strength

On very windy, exposed sites, extra steel cross braces help to strengthen the structure. These also offer a useful way of maximising growing space, allowing gardeners to suspend a shelf on which to house container-grown plants. Installing a basic electrical power source (a weatherproof, double socket) is also very worthwhile, as it allows the use of heated propagators and heated plant mats (see fruithillfarm.com). You could even install basic overhead lighting for those dark winter evenings. A nearby water supply is also essential, while some form of irrigation system (ideally drip irrigation, also available from CWP) is both effective and time-saving.

Finally, think long and hard before attempting to save costs by choosing the DIY option when it comes to erecting and covering your polytunnel. Unless you’re possessed of large reserves of patience and a natural knackiness, that way lies madness. (see cwp.ie)

This week in the garden…

Start browsing the catalogues of seed and summer-flowering bulb suppliers and compiling a wish-list so that you can place your orders in plenty of time as supplies of some of the more unusual or hard-to-get varieties can often run out.  While many companies still post out catalogues, it’s often easier, faster (and a little kinder on the environment) to browse them online.

Use a sharp secateurs to cut away the old leaves of hellebores. Not only does this make the pretty flowers more visible but it also minimises the risk of diseases such as leaf spot. If you didn’t get around to giving the plants a light mulch of leaf-mould or garden compost last autumn, then take the opportunity to do so now.

If you have a window-box or container filled with winter-flowering bedding plants such as pansies or polyanthus, then take a few moments to deadhead them in order to encourage the production of new flowers. Remember that despite the cooler temperatures, winter containers can still suffer from lack of water, especially if they’re under an overhanging roof or ledge. Check by gently sticking your fingers into the compost and if it feels dry, then water moderately.

Dates For Your Diary… Wednesday, January 11th (8pm), Kill o' the Grange parish centre, Kill Lane, Blackrock, Co Dublin, "A Passion for Peonies", a talk by Dr Philip Havercroft of Leamore Nurseries on behalf of South County Dublin Horticultural Society (visitors €5).