What Is My Microclimate?
Even across a small area, microclimates allow 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 or oregano will thrive in the additional reflected heat and light from the paving. Wind damage caused by gusts and eddies swirling around solid barriers is nearly as bad as that of unchecked wind. Semipermeable 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.
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 yard, 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 from 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.
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 and 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 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.