Your Garden's Microclimate

Posted on: 31 March 2008 by Gareth Hargreaves

Understanding your microclimate will help you make the most of the garden you've got.

Microclimates are local variations in the general climate - they can include soil type, exposure or shelter, and sun or shade. Understanding microclimates enables you to exploit them to your advantage. Even across a small area, there will be enough variation to grow a broader range of plants than you might first think.

Microclimates can even be created; for example, when laying a patio, leave a few gaps between paving slabs and fill them with gritty soil to make planting pockets. In a sunny spot, drought-tolerant herbs like thyme and oregano will thrive in the additional reflected heat and light from the paving.

Wind Turbulence

Wind is probably the most important factor in the garden environment. Gales and storms can cause substantial physical damage, but even normal breezes have an impact because they dry out leaves and plants will need watering more often. Even in a small garden some areas may be more exposed to wind than others.

Wind turbulence is caused by solid walls, fences, and buildings as the wind tumbles over them, creating an eddying effect. You can reduce the problem by using barriers that let some air through. Try to identify the windier or more turbulent parts of your garden and reduce the problem by planting hedges or living screens. A barrier to wind can shelter an area of garden behind it equivalent in length to five times the barrier's height.

Wind disturbs the moist air layer on the surface of leaves, making them lose water more quickly than on a still day. As the plants begin to dry out, the leaves close their pores. This prevents carbon dioxide getting into plants, and photosynthesis - and therefore growth - stops. This is why plants grow best in the shelter of hedges and fences.

Shelter belts slow wind speed over some distance, creating a niche for large, leafy plants that can be made ragged or lose too much water in a breeze.

How To Garden - wind barrierWind damage caused by gusts and eddies swirling round solid barriers is nearly as bad as that of unchecked wind. Semi-permeable barriers, such as trees and shrubs, hedges, trellis, or non-solid walls and fences, provide more effective shelter. They may also cast less shade, and don't completely block your views.

Sun Traps

Walls and greenhouses will absorb heat in the sun, then release it slowly later. Walls can also create frost shadows, so placing containers against them during winter will help to keep plants frost-free; a tender azara, for example, will exploit the conditions found in a very sheltered corner of the garden and help brighten up a dark spot.

South-facing walls reflect heat, so provide the perfect planting opportunity for less hardy plants. They are traditionally used for growing and ripening fruit like peaches and plums, and for ornamentals such as roses, which may flower earlier due to the extra warmth.

Frost Pockets

Frost pockets form as chilly air sinks to the lowest point it can. Areas at risk include dips, valley bottoms, and places where cold air can collect behind a barrier. Slopes are generally dry because water runs to the lowest-lying areas in a garden. Lower areas may also be more prone to frost, because cold air sinks. The combination of frost and wet soil is especially damaging, and only fully hardy plants will tolerate such conditions.

How To Garden - shadeDeep, damp shade is ideal for lush, leafy plants that dislike high temperatures. Damp shade can either be sheltered and relatively frost-free or, if a barrier such as a hedge or fence is creating a frost pocket, be cold and slow to thaw in winter.

The ground at the foot of a wall will be sheltered from rain; sun-loving plants, such as the alstroemerias pictured above, will thrive there, although they'll need extra care while they establish.

How To Garden bookThis extract is taken from DK Royal Horticultural Society How To Garden, which you can purchase at all good book shops or online from Amazon.

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