A region’s climate is made up of its precipitation patterns, average temperatures, and number of sunny or cloudy days. A microclimate consists of similar components, but refers to a very small location.
A microclimate is similar to site conditions, but doesn’t include features of the soil. Instead, it includes factors such as shadiness and wind.
A small urban yard often includes many microclimates. The spot under the leaky gutter will get much more precipitation than the average for the region, while the strip under the eaves will be dry and shady all year round.
Just like with site conditions, matching plants to microclimates will help them thrive. Simple observation can reveal microclimates in a yard: observe which areas are dry or wet after a rain, or watch to see where snow melts first and where it lingers longest.
Plants respond to microclimates, but also help to create them. Adding or removing plants changes patterns of shade, wind movement, and water flow. Installing a plant that can tolerate a currently-existing microclimate can thus help create favorable conditions for adding a more sensitive plant later.
Microclimates can create other interesting opportunities as well. The warmest spot in your yard may be a suitable location for a plant that would not normally survive in your hardiness zone.