While hardiness zones are a useful resource for planning a planting schedule, microclimates are the true indicator of when it is time to plant. Just as air temperatures can vary from one side of town to the other, the temperatures in your backyard garden can be different than your neighbor’s garden.
Several factors come into play to create large-scale microclimates, including urban areas, hills and valleys, shade and protective structures (like walls) or proximity to large bodies of water. There’s not much a gardener can do to change these environmental factors. In your yard, your home and other structures create the microclimate aspects you can control to some extent:
- Your house — Like buildings in an urban area, your home can radiate heat. In addition, the house can block wind or sunlight from reaching the garden. Keep in mind your garden’s orientation with respect to your house.
- Balconies and rooftops — Because of their height, plants grown on rooftops may escape frosts that kill tender plants at ground level.
- Fences, walls and large rocks — These structures can protect plants from wind and radiate heat, creating sheltered spots.
- Raised beds and terraces –These warm up faster and drain earlier in spring, especially if they are facing south.
- Paved surfaces – Patios, driveways and sidewalks absorb and radiate heat, which can raise nighttime temperatures.
- Trees– Trees can prevent rainwater from reaching the ground and compete for water with other plants, making it difficult to grow new plants near a tree’s roots.
- Soil types – Clay soils can act like paved surfaces, heating the temperature near ground level. Lighter soils with many air pockets can insulate the warmer soil below, trapping heat below ground and making the ground level more frost-prone.
While you may not be able to tear down buildings or trees, using soil amendments and planting at different height levels can help you make the most of your garden’s unique climate.