Baby it’s cold outside
Our winter survival guide for your plants
Sheesh, it’s been cold . . . or at least, in my garden it’s been cold. Cold enough for frost, ice and even snow, if only a barely there dusting of white.
Cold enough that the soft foliage of tender and half-hardy plants which were in flower only weeks ago has now been blackened, while I’ve taken to wearing a double layer of gloves while I finish planting the last of the spring bulbs. But then my garden – a frost pocket at the bottom of a damp hillside and at an altitude of 230m, is colder than most – while I, to my vague embarrassment (the firmly held view is gardeners should be a hardy lot), feel the cold more than some.
It is consoling to know that the same can said of many plants. Take the exceptionally cold winters of 2009 and 2010, when traditional garden favourites such as phlox, oriental poppies and hardy geraniums proved their ability to withstand temperatures as low as minus 17 degrees. Others didn’t, including many specimens of ceanothus, tree ferns, large-leaved hebes, bay laurel, fatsia, rosemary, phormium, cordyline, cistus, olearia and pittosporum.
Why so? The answer is that a plant’s hardiness depends on a vast and sometimes baffling range of factors, chief among which is its natural habitat.
Along with native plants, our gardens are filled with a rich variety of flora that originated in faraway places – in Europe, Asia, Australia, North and South America – and which evolved under a great diversity of growing conditions that influence their coping mechanisms when it comes to withstanding the stresses of extreme cold, heat, drought or flooding.
One example is the aforementioned choisya ternata, or Mexican orange blossom, that evergreen, flowering shrub so popular with Irish gardeners but one which was badly hit by those two recent harsh winters. It is not native to Ireland but to Mexico, where it grows on chalky soils in coastal areas.
As for the lovely, large-leafed fatsia Japonica that’s a feature of many smart town gardens? As suggested by its species name, it is native to Japan.
And the scarlet-pink fuchsia hedges of west Cork and Kerry? That is fuchsia magellanica, a species native to temperate regions of Chile and Argentina,.
Given such a great diversity of garden- worthy plants, horticulturists have come up with various systems that help us to gauge their individual hardiness, including the American USDA system and the freshly revised RHS system, the latter of which now rates individual plants on a scale of one to seven
At the most tender end of the RHS scale are tropical greenhouse plants (H1a) that require heat all year round, while at the other end (H7) are the many ultra-hardy plants that should survive the coldest of Irish gardens and the harshest of winters, to temperatures as low as at least minus 20 degrees.