What will grow in this spot?–Climate Zones & Microclimates
Proper placement of plants in the landscape is critical to gardening success. One of the most challenging jobs at the nursery is figuring out where to put plants to grow them on so they will grow strong & healthy and most importantly– not die. Knowledge of the specific needs of each plant species is essential and is probably the most important reason to consult a professional horticulturist or experienced gardener when investing in plants for a new landscape. Even some landscape designers, although they may come up with beautiful plans, are sometimes weak when it comes to knowledge of how specific plants will perform in their intended locations.
Many garden books refer to the USDA Plant Hardiness Zone Map which shows the average minimum temperature for each area. It is really only useful to tell you which plants may be killed in winter. The Puget Sound region is in zone 8b (15-20F); this is the same zone listed for Austin, Texas and Gainesville, Florida. Sunset Western Garden Book zones are more helpful. Our Sunset zone is 5–“Marine influence along the Northwest coast, Puget Sound and Vancouver Island;” it takes into account our longer growing season and relatively cool summers with low heat accumulation.
These zone systems are helpful to determine what plants will grow in our region, but other factors such as the amount of light and moisture, and type of soil will influence what will grow in a particular location. Most garden books will tell you whether plants need full sun, partial shade or full shade, and may also tell you their water requirements. When planning a landscape it is important to be aware how much shade an area will get throughout the day– from trees or buildings. Although the Northwest is famous for its rain, July & Aug. are usually dry. Many of our native plants are actually killed by summer irrigation. It is best to have separate areas for water-loving plants and those that need it drier.
The type of soil you have in your yard may also limit what you can grow. Most of our soils, derived from glacial till, are sandy loam to clay loam, with medium acidity, and moderate to high organic matter. You can usually improve soils by the addition of organic matter, but it is more difficult to correct drainage problems. Nonnative plants may benefit from an application of lime to raise the pH of the soil.
Topography has the biggest effect on microclimates. It can affect temperature, light, moisture, and soils. A southern or western slope will be warmer, brighter and drier than a northern or eastern slope. Cold air, like water, will drain down to the bottom of hills & depressions. Soils are also shallower on steeper slopes.
Buildings and other structures, similarly, may create microclimates. Urban environments are much warmer than rural areas due to concrete and asphalt absorbing and retaining heat. The south and west side of buildings are much warmer due to the same “heat sink” effect of many building materials. Conversely, buildings create shady areas on their north and east sides. Nurseries often build shade houses to shelter plants that grow better with less sun. Fabrics with different shade ratings draped over an open structure, have mostly replaced old-style lath houses.
A little research on the plants you plan to buy will help to ensure that you can match them with their intended location. Putting the right plant in the right place will increase your gardening success–but weather anomalies will always create challenges even for experienced gardeners.
(This article was first published in the Peninsula Gateway on August 17 2011.)