How to Deal with Climate and Microclimate in your Garden
Geographical location
Climate is all-important because it dictates the kinds of plants you can grow and exerts an immense in¬fluence on design. If you have moved to a new area it is easy to discover average temperatures and rainfall, but you must always allow for extremes.
Regional climate is influenced by fundamental geo¬graphical factors like latitude, altitude, proximity of large land masses and the sea and the influence of ma\or ocean currents. Every district has its own special quirks too, such as the Mistral, a cold wind funnelled down the Rhone Valley in France, the “Fremantle Doctor”, a cooling wind that relieves the inhabitants of Perth in Western Australia from heat¬waves, and the high altitude of the Alps and Rockies that shortens the growing season.
Then there are microclimates, natural and arti¬ficial. For example, in most winters central London is nearly frost-free because of the artificial heat exuded by the city. Consequently many tender plants like cer¬tain abutilons can be kept outside while in colder country areas they have to be tucked up in a con¬servatory over winter. More surprisingly, given the northerly latitude, gardens on the northwest coast of Scotland can grow subtropical plants outdoors with minimal risk of damage because of the moderating effect of the Gulf Stream. In the Pacific Northwest of the United States the climate is made more temperate and wetter than adjacent regions by warm Pacific cur¬rents, giving milder winters than are found in the more southerly Kansas.
Though it is wise to learn about your local climate, it is equally important to set about creating your own special microclimate. You cannot do much about the weather but you can do a great deal to minimize its effects, perhaps by erecting a protective windbreak against slicing, icy winds. Often, famous established gardens succeed because their creators have taken great care to improve conditions, enabling them to grow a wider range of delicate and more interesting plants. In cold areas frost and snow do no harm pro¬vided you are growing hardy plants and no tender perennials have been left outside. A much bigger problem is wind. It dehydrates soil and stunts growth, while constant buffeting bruises young, emerging plant tissue, impairing growth and develop¬ment. The first task, therefore, in trying to influence the climate in a new garden is to eliminate or at least reduce the potentially destructive wind.
Creating shelter
If the site is badly exposed, conditions may be too un¬pleasant for even shelter plants to establish them¬selves, in which case you will need to erect either tem¬porary or permanent windbreaks. Although it may seem like a good idea to build a solid wall, this does more harm than good. The wind will eddy over the top of the wall and swirl down, creating a whirlwind effect in the garden. The only solution is to create a filtering windbreak that is approximately 40 percent porous, which reduces wind speed but does not stop it dead. Since the screen should become an attractive garden feature rather than a simply functional object, plants are preferable to fencing, but they do, of course, take longer to develop.
Windbreaks usually protect an area ten times their height, so they will produce an immediate change to the growing conditions within the enclosure. For example, two of them running from east to west on either side of a garden will create a dark, cool side and a warm, well-lit one. The advantage of such a wind¬break is that it provides an opportunity for two contrasting garden areas, each with its own range of plants, each with its own character.
The type of screen chosen depends on personal pre¬ference. Walls will need to have trees or shrubs planted nearby to minimize the eddying effect of the wind; evergreens or matching shrubs successfully complement such solid structures. Alternatively, consider hedges, whether clipped formally or kept in trim with an annual haircut. For a more natural look, thickly planted shrubs, interspersed with taller trees, create a good shelter belt. The selection of plants should ensure a changing pattern of interest running through the seasons with spring blossom, fresh, ex¬citing contrasting foliage in summer, autumn berries and interesting twigs, branches and bark over winter. Pay particular attention to colour, texture and out-fine. With thoughtful planning you will be able to create an outstanding garden feature which is also functional. This does not have to be formal and sym¬metrical; a seemingly random planting will blur the garden boundary and give the illusion of space.
Frost
Frost in winter is seldom a problem unless you want to grow bananas outdoors in upstate New York or daturas on the Cotswold hills. Given that there are in excess of 60,000 hardy plants to choose from, even the coldest areas can be planted up to suit most tastes.
Frost at the wrong time of year, on the other hand, is disastrous. It kills tender young growth, destroys spring blossom and, in extreme cases, wipes out whole plants, especially the marginally hardy. The most likely scenario for unseasonal frost is a clear, still night which follows a calm, bright day. Without wind currents to move it, cold air accumulates in low places, like water forming a pool at the lowest level. The problem with erecting shelter is that it increases the danger of untimely frost by damming up cold air. This is particularly likely on a hillside or in a hollow and is known as a frost pocket. A natural frost pocket cannot be eliminated, but you can at least reduce the problem by creating perimeter gaps so that the cold air flows out of the garden and away.
Having said that, though, it is worth stressing that winter frost can be a fantastic advantage. This is parti¬cularly true of gardens strong on structure, with topi¬ary or with clipped low hedges roping in different areas. Not only can the form of plants be more clearly appreciated than in summer when they are usually part-hidden by flowers, but such architectural shapes look quite sensational when crested with frost. The same goes for the herbaceous border. Many gardeners cut down the straggly growth in autumn, but this can easily be left until the following spring so that it, too, will give a fine display of mid-winter, frosty outlines.
Tags: artificial heat, gardener, greens, tender plants, tropical plants