Thriving Plants & Hardiness Zones: Tips from Portland Landscapers
The exclamation “Location, location, location!” is typically applied to the world of real estate, but it applies equally well to gardening. Landscaping experts the world over appreciate the importance of selecting the correct plants for local climates. In this post we go into detail about location-based landscaping in Portland. We discuss climate zones and hardiness zones, two measuring sticks that green thumbs use to categorize which plants will thrive where. We also touch on which plants thrive in Portland.
Portland landscaping experts know that our locale is a gardener’s paradise. The Rose City is well known for its greenery, and many plant species thrive here. However, even in Portland, it can be difficult to figure out which plants will succeed, and which ones will not make it through our long rainy season. Although Portland temperatures are mild for most months of the year, we do see freezing temperatures that may last several weeks. This tendency makes it challenging for certain plants to survive. Rather than guess willy-nilly which species will be able to make it here, many local gardeners refer to each plant’s hardiness zone rating.
Hardiness zones can be confusing because there are two distinct classification systems that are used to determine a plant’s hardiness (i.e., its ability to survive cold winters). Let’s take a look at both of these systems.
USDA Plant Hardiness Zones. The USDA plant hardiness zone schema was rebuilt in 2012 with the help of researchers from Oregon State University. The updated system that was released in 2012 utilizes GIS mapping data, and provides detailed information about average minimum temperatures for each state. USDA Plant Hardiness Maps may be used to determine if a plant is expected to survive winter in your given hardiness zone.
Sunset Hardiness Zones. Sunset Hardiness Zones are different. Produced by Sunset Gardening Magazine, Sunset Hardiness Zone Maps tend to be significantly more detailed than the USDA plant hardiness zones because they include more factors, including elevation, humidity, latitude, ocean influence, microclimates, and more.
What zone is Portland in? Portland falls into USDA hardiness zone 8b (with average low temperatures from 15 to 20 degrees Fahrenheit) or 9a (with average lows from 20 to 25 degrees Fahrenheit) for parts of inner Portland. Portland (and the entire Willamette Valley) is in Zone 6 according to the Sunset rating system. It is interesting to note that the 2012 updated version of the USDA hardiness zone map reflects a trend of overall warmer temperatures since 1975.
Planting in the Right Spot
To plant or not to plant is often the question for gardeners. Portland is the land of microclimates, so the hardiness guides are recommendations at best. Nothing beats gardening experience for intuiting which plants will survive winter, and which will not.
Having an understanding of your local microhabitat is very helpful when deciding which species to plant. Gardeners who are accustomed to conditions on the valley floor will find it difficult to grow the same species at the top of Council Crest, where the elevation is around 1000 feet. Your own yard will almost certainly contain microclimates as well. For example, a shady corner will not warm up as quickly as a sunny spot, and you may find areas that offer more shelter, which can therefore support more temperature-sensitive species. Many Portland gardeners let experience guide them—if something does not work, they either strike that species from their shopping list, or they treat it as an annual in following seasons.
The ability of a plant to perform depends on many factors, including the gardening care given, soil types, available nutrients, proper irrigation, and more. Knowing the plant’s needs will help you select a spot where it is likely to thrive. The USDA and the Sunset Gardening plant hardiness zones can inform your decision of which plants to include in your garden.
Hardiness Zone Tips from Portland Landscapers
Zone 6. Portland is in Zone 6 according to the Sunset hardiness system. Gardeners in this zone enjoy a long growing season (from mid-March to mid-November), but they also experience the possibility of cold snaps and/or long winters. Seasonal storms can make gardening unpredictable, but in general the summers here are dry and hot, while the winters are wet and cold.
What to grow? There are dozens of perennials and shrubs that do well here. In the full sun you are likely to find:
• Bee Balm
• Purple Cone Flowers
• Black-Eyed Susan
• Coral Bells
In the Portland shade we find:
• Solomon’s Seal
• Hellebores, and more.
Shrubs that thrive in Portland include:
• Butterfly Bushes
• Witch Hazel
Coniferous and deciduous trees of all sizes and shapes grow here, including Alders, Birches, Beeches, Pines, Douglas Firs, and Cedars. Portland is famous for its Monkey-Puzzle Trees. This enormous, unusual coniferous plant first arrived with the 1905 Lewis & Clark Exposition, a Portland event at which dozens of small Monkey Puzzle trees were handed out to residents. Shrubs such as Mahonia and red flowering current also do very well in a Portland landscape.
Looking for more? Great Plant Picks is a terrific site that is a part of the Elisabeth C. Miller Botanical Garden. This site contains recommendations on over 900 exceptional plants that have been selected for gardeners living west of the Cascades, from Eugene up to British Columbia. This searchable resource includes helpful lists of plants for sun and shade. It also boasts plenty of extra information on participating nurseries, useful websites, organizations, and more!
If you fall in love with a particular plant, even if it isn’t zoned for our area, we say why not give it a home in your garden? Just make sure to consider it an annual. After all, you may luck out and Portland will have a particularly mild winter that your new plant will make it through just fine. If this is the case, you will be able to enjoy it for a few more seasons. And let’s not forget, even the best gardeners will lose a few plants over the course of their gardening career, even ones that supposedly should do just fine in our climate—so you may as well choose to plant the ones that you love! If you’re aware that a certain plant is highly unlikely to survive the winter, you can also choose to keep it in a pot and bring it inside for the winter.
For more advice on which plants shine in Portland’s climate, give us a call! Our Portland landscaping experts can recommend the perfect planting for your yard.
Rebecca Smith is a Design/Sales Associate at Landscape East & West. She has an A.A.S in Landscape Design and Landscape Construction from Portland Community College. She enjoys spending as much time as she can gardening and being outdoors and is passionate about helping clients transform their outdoor spaces.