Water-Wise Planning and Design (II)

Creating Microclimates

One of the most important and enjoyable aspects of gardening is addressing microclimates.

Microclimates result from differences in sun exposure, shade and wind patterns, and topography in a given area. A microclimate may be brought about by elements including a building, tree, or even by a large rock. Microclimates can create hotter, cooler, windier, wetter, or drier conditions than the norm, and will greatly affect the growth and well being of plants in your garden.

Microclimates may be used advantageously to provide shade and also protection from winds. They can contribute to keeping the landscape cooler, reducing water loss, and creating a comfortable, pleasant living environment.

The basic microclimates in your site should take the four main exposures (south, north, east, and west) into consideration.

Southern exposures get more sunlight on a regular basis than other exposures, and therefore are suitable for plants that naturally grow in full sun. Areas with southern exposures are relatively warm, and have higher water evaporation rates, which results in drier soils. They may be shaded easily in the summer with overhangs planted with vines such as Campsis radicans (Trumpet Vine), or with large deciduous canopy trees such as Albizia julibrissin (Silk Tree). They generally provide an ideal orientation for an outdoor winter zone.

Northern exposures may experience shade year-round and therefore are suitable for plants that prefer cool, moist, and shaded areas such as Acanthus mollis (Bear’s Breech). Northern exposures are suitable for providing a cool outdoor living area in the summer.

Eastern exposures receive morning sunshine throughout the year and provide relief from the afternoon sun. They are protected from the prevailing westerly winter winds and generally are characterized by more moderate temperatures than southern and western exposures. They need protection from the low morning summer sun, and this may be achieved effectively through the use of large deciduous ornamental shrubs such as Buddleia davidii (Butterfly Bush) or small trees such as Lagerstroemia indica (Crape Myrtle). Areas with eastern exposures generally are suitable for plants that are native to sunny regions.

Western exposures provide morning shade but receive afternoon sun, which usually results in intensely hot conditions in the summer. Consequently, the soil suffers greater temperature swings and more rapid drying in comparison to other exposures.  In winter, the cold northwesterly winds can damage plants.  Therefore, dense planting with windbreak trees such as Cupressus sempervirens (Italian Cypress) and also with large canopy trees such as Certonia siliqua (Carob) is advisable for this exposure. This combination serves to provide protection from both the cold winter winds and the hot afternoon summer sun.

For a wide selection of plants that are suitable for different exposures, look at the plant lists in the Water Conserving Landscapes section of the CSBE web site.

Finally, keep in mind that microclimates greatly affect the water needs of plants. Southern and western exposures generally need more water than eastern exposures; northern exposures need the least amount of water.