When people list history’s most world-changing inventions, they usually include fire, or guns, or computers. Rarely do people mention something so ubiquitous to us that it has become, literally, invisible – glass and transparent plastic. Glass was known to the ancients but rare -- Job 28:17 lists it with gold among the most precious of materials. In the Renaissance, though, when glass began to be sheeted and shaped in quantity and with skill, it created a boom in civilisation; microscopes and telescopes opened up the breadth of the world to science, spectacles doubled men’s intellectual lifetime, and windows allowed for the creation of the first greenhouses.
We spend so much technology and energy -- electricity, oil and coal -- to heat homes against the weather, altering it to suit our needs. Properly-placed windows, however, allow the sun to do our work for us, allowing light in and slowing the passage of heat out. Even when the temperature outside dips below freezing they keep out frost, and allow the gardener to more easily control water, pests and wind-blown seeds.
Nowhere, perhaps, is this more important than in a land like this, a nearly subarctic island kept mild by the Atlantic current, where the climate usually hovers just below the ideal range for many vegetables. Here, greenhouses extend the growing season by months and create pockets of Italy or Illinois in, say, the cold bogs of County Kildare.
Here and in Britain, greenhouses, cloches and coldframes allowed Victorian master gardeners to grow a range of seemingly impossible crops: not just tomatoes and aubergines but melons, lemons, limes, grapes, olives and peaches. Pineapples, for example, became a status symbol among the manor-born, and banquets sported them as a centrepiece.
Greenhouses remain a worthwhile, albeit expensive, investment for most people in most climates. If you want to start small, though, you can create cloches, transparent coverings for one or a few plants each. Victorians, again, mass-produced glass bells to cover plants to create a microclimate inside. You can do the same thing, however, with soda bottles.
To make a cloche, cut the bottom off an old two-litre bottle and place it around a seedling in the garden. Once the bottom is off, the plastic becomes very flimsy, so you might want to bury the edges several centimetres deep to keep it stable. Alternately, you can place a ring or solid structure inside if you have one, something that will keep the bottle in place but allow the seedling to grow. Or you can place it around a flowerpot whose diameter is smaller than that of the bottle.
Cloches, like greenhouses, allow you to regulate the amount of water a plant receives – here that means not getting waterlogged in the rainy winter. You might want to keep the caps of your soda bottles in a drawer, so you can put them back on at night if it gets too cold.
A step up from a cloche is a row cover, something to put over an entire bed. We clamped flexible plastic piping over our raised beds to make hoops, draped clear plastic over them and secured the plastic to the wood below the hoops with staples. Alternately, instead of plastic, you could put horticultural fleece over another raised bed, to keep in the warmth – we did both this year, and gave our plants such protection that our corn salad survived the month of snow and ice.
If you want to go sturdier still, you can build a coldframe, especially if you have old windows you can use. A coldframe is just a box with glass or transparent plastic on top, ideally with a top slanted toward the south. Fill the box with earth and plant seeds inside, and over the slanted top secure a sheet of glass or whatever you have. You could install the window frame with hinges at the top for maximum convenience, but just taking off the glass gently will do.
If spring and autumn nights get very cold where you live, you could insulate the back and sides with anything from straw bales to foam. People around here used to combine coldframes with manure composters; since manure gives off considerable heat as it matures into soil, they filled a coldframe partway with horse manure, put soil on top for the seedlings, and gave the baby plants warmth from above and below.
Polytunnels are an excellent means of creating a walk-in garden for a fraction of the cost of an old-style greenhouse. You can get one as small as a closet or as large as a warehouse, and most are guaranteed for a decade or two. We had to tear down our old one to build our house, but it had lasted almost 20 years, and we installed the new one two weeks ago.
If you have old windows, or sheets of glass or clear plastic, you could try building a greenhouse out of cob. To do this you would stack rocks to make a low wall – say, half a metre to a metre high, depending on how high the snow or moisture get – and then build upward with a well-mixed and kneaded blend of sand, clay and straw. The walls could be built upward with large holes on the south side, and the cob could be plastered around the glass to keep them in place. Such a project would consume a lot more time and labour – we have day jobs, and didn’t take this route – and it would not in as much light as an all-clear home. It has the advantage, however, of being potentially free and using all-local materials.
Since you put such care into creating a greenhouse of some kind, make sure you have good fertilised earth in it – many warm-weather plants, like tomatoes, also need a great deal of nutrition, and gardeners used to sprinkle potash and other supplements around them.
In years to come we might not be traveling as much as we used to, but with the help of a little store-bought or scavenged material, you can create, in your own land, a patch of somewhere else.