Sunday, February 28, 2010

Mediterranean climate

Believe it or not, the Seattle area is considered to have a “Mediter-ranean” climate.  Well, it depends on whom you ask. Factors such as amount of winter rainfall and specifics about latitude result in disagreements. According to the Koeppen climate classification, we fall within a cool, dry-summer subtropical zone (Csb), resulting in Mediterranean characteristics.  Some diplomatic experts call it “modified Mediterranean.” Whatever.  I decided to try to understand the classification and how it affects our gardening.

Over 50% of the regions that boast this climate are located around the Mediterranean Sea, hence the name. The defining characteristic is the wet winter/dry summer seasonal changes in precipitation. Mediterranean zones are situated in either hemisphere on the western side of continents, between latitudes of 30° and 60°.

During the summer, this climate is dominated by subtropical high pressure cells making rainfall unlikely. During winter, prevailing winds from the west blow from the sea bringing rain and stormy weather. In addition, most areas with this climate, such as Seattle, are backed by coastal mountains. The warm moist air from the ocean rises up the mountains, expanding and cooling. At the dew point, the moisture condenses and precipitates on the mountain's windward side. The climatic and geographic effects combine to result in high seasonal rainfall totals.

In fact, areas with this climate receive almost all of their rainfall  for the year during the winter season, and some may go 4 to 6 months in the summer without having any significant precipitation. Our summers are shorter because as you move north along the American west coast the winters become more intensely wet and the dry seasons shorter. Interesting!

All regions with this climate type abut large bodies of water, moderating the temperature. Comparatively, there is a small range of temperatures between the winter low and summer high. The mildness varies with altitude, elevation, and distance from the ocean.

Mediterranean climate regions support some of the highest diversity of species in the world.  While these regions cover only 2% of the planet, they contain 20% of the world’s plant species. It is a gardeners’ paradise! I’ve lived in Texas and New Mexico and I can tell you by comparison, we can grow A LOT of different kinds of plants here. Our diversity is quite remarkable. How does all of this affect the way we garden?

Smart gardening takes more into consideration than “what we CAN grow.” Our job becomes substantially easier and more practical if we select plants that thrive without coddling. Despite the prodigious number of days we receive rainfall, our summers are DRY. It makes sense to accommodate that reality. As you contemplate acquiring new plants, put some thought into how much watering they are going to require. If you can’t live without those water craving prima donnas, plant them all together not spread out through the garden.

Check out the drought tolerant (xeric) planting areas of local public gardens. For my area, that includes the Bellevue Botanical Garden and the Center for Urban Horticulture Mediterranean(CUH) in Seattle. The Miller Garden in Seattle has a lovely Mediterranean hillside  facing west. Peruse the planned borders featured at High Country Gardens and see how beautiful xeric can be!  The Elisabeth Miller Library has resources including a list of books. Educate yourself now and enjoy the results this summer!


  1. There are always unusual situations,i.e. when we were snowed in on Christmas with 6" of snow! Am I wrong? Or does it snow in the Mediterranian?

  2. Indeed it does snow here, almost every year. In the classic Mediterranean climate, temperatures during winter only occasionally reach freezing. Snow rarely occurs at sea level, but often in surrounding mountains due to wet winter conditions. Usually our snow is a result of cold air coming off the Gulf of Alaska. Italy doesn't have to deal with that-although the closer you get to the Italian Alps, the more snow you have.