Across a permaculture site, there are few things that are uniform. With biodiversity and the maximization of edge key principles in permaculture gardening, you site is unlikely to look very uniform, not to mention that each individual plant grows in its own unique way. But also, your site is unlikely to feel uniform. Across a single location, there can be a significant number of different microclimates. These microclimates have different atmospheric conditions from the areas they are next to, with variations in temperature, light and water all likely to be present.
The good news is that once you understand how different factors affect microclimates, you can modify those factors through your design to create, change and improve the microclimates on your property.
There are five main factors that affect microclimates.
The shape of the land is a significant influence on microclimates. While on a large scale, weather systems have a certain predictability (related to the rotation of the earth and the interplay between ocean and land), these patterns can get disrupted at the local level by topographical features such as aspect and slope.
Aspect refers to the direction that a slope faces. This will determine how much solar radiation it receives, which in turn impacts upon temperature and shading. In the northern hemisphere south-facing slopes are exposed to more direct sunlight than opposite slopes, as are north-facing slopes in the southern hemisphere. This will cast longer shadows on the opposite side of the slope, which must be taken into account when deciding which species of plant to place there. (This is also the case on flatter ground where trees, hedges, fences and walls cast shadows.) Even small dips and indentations on your property can affect the microclimate, as they can form collection points for cold air and as a result sometimes form frost pockets.
The angle of slope on a geological feature is a major factor in determining the influence of wind and water on a site. The steeper the slope the faster wind will move uphill. This can impact not only on vegetation on the windward side, but also cause increased turbulence on the leeward slope as the wind falls back down on the other side of the slope. The appropriate placement of windbreaks can help to alleviate these effects, while if you do have steep slopes on your site that create a lot of wind, you may wish to investigate harnessing this energy with turbines.
In terms of water, a steeper slope means that water runs off the slope more quickly, meaning not only that it has less time to percolate into the soil and so be made available to plants growing there, but also is more likely to cause erosion of the soil on the slope, particularly in areas of heavy rainfall. Furthermore, the position of your property in the landscape will affect temperature, with locations higher above sea level being colder than those lower down.
The composition of the soil affects microclimates primarily through how much water it retains or which evaporates from it. A soil that has a large proportion of clay retains more moisture than one that is predominantly sand. The degree to which a soil retains moisture affects the humidity and temperature of the air above it. After heavy rains, the soil can contain a lot of water and modify microclimates much like a body of water such as a lake.
Besides the mineral composition of the soil, the degree of coverage it has will affect temperature and moisture evaporation. Bare soils reflect more light and heat than those covered by plants or mulch.
It is not just the moisture level within the soil that can affect a microclimate, the water stored on the surface of the land is also important. Over a region, the presence of lakes and reservoirs can create a more moderate climate, while ponds, streams and other bodies of water on your site will impact upon the temperature of the surrounding areas in your garden. These effects are due to the fact that water gains and loses heat more slowly than the land.
The water body also sends moisture into the air through evaporation. This atmospheric moisture captures heat from the sun, making the air around a pond warmer than areas further away. The moisture in the air around ponds can also influence the plants your place there, with species favoring a more humid microclimate likely to thrive.
The vegetation on a permaculture site interacts with the soil and water to affect the microclimate. Not only does it cover the soil and prevent heat loss and radiation from it, it also regulates the temperature of the soil, filters dust and other particles from the air, and can act as a windbreak or suntrap.
Vegetation is naturally adapted to make the most of its climate of origin. So, for instance, plants that originate in tropical areas tend to have broad, dark leaves that allow for the maximum absorption of sunlight, and the effective transpiration of moisture back into the air – which will in turn influence the microclimate in the immediate vicinity. Use native plants in your permaculture design to make the most of these adaptations.
Your house can impact upon microclimates by absorbing heat during the day and releasing it at night, by deflecting wind and creating sheltered spots, and reflecting sunlight. But other artificial structures can also play a part in modifying microclimates. For instance, patios and other paved surfaces like driveways moderate temperature by absorbing and releasing heat, while fences and walls can give plants protection from wind, shade and shelter from wind. Even rocks in the garden will have an impact by storing and releasing heat. You can judiciously place rocks to modify microclimates.
Microclimates are dynamic things. As your site changes through maturation of planting, siting of artificial structures, and even contouring of the land, so the microclimates will alter. The good thing is that you can directly influence how this happens by your design choices, and so make the maximum use of every microclimate niche on your property.