What is a microclimate?
By definition it is the climate of a very small or restricted area, especially when this differs from the climate of the surrounding area.
How does a microclimate work?
One example would be planting a plant on the north side of your home. If you plant it against the house you'll have shade for the majority of the day, protection from southwest winds, and warmer nights due to the house retaining heat. This would allow a plant that might not grow in full sun and is sensitive to hot winds to grow without issue. A perfect example of this in the High Desert would be a Japanese Maple. The USDA zone would be 5-8, and the Sunset Zone would be 2b-10. We live in Sunset zone 10 and USDA zone 9. Will these grow here? Yes. Will they grow as the main shade tree in the middle of your yard without protection? Absolutely not. This is where the knowledge of microclimates dictates what you can plant more so than the USDA zone that is placed on the label.
What are examples of a microclimate?
A few examples of microclimates in a residential setting would be:
Planting near a building - additional cold tolerance due to heat, especially on south side
North side of a building - wind and full sun protection
Sloped ground - can create variance in wind direction and cold pockets of air
Low point in the yard - sometimes creating a pool or pond