- Thriving Plants & Hardiness Zones: Tips from Portland Landscapers
- The best gardeners know USDA and Sunset zones
- Prune fruit and nut trees in early spring
- Oregon’s stake in $6 trillion prospect
- Oregon Planting Zones – USDA Map Of Oregon Growing Zones
- Gardening in Oregon – Flower, Shrub and Tree Planting with the USDA Plant Map
- Landscape Plants
- Gardening in the Pacific Northwest Region
- Can I Plant a Palm Tree in Portland?
- What are Plant Hardiness Zones?
- What are Microclimates?
- USDA Planting Zones
- Choosing Plants
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.
The best gardeners know USDA and Sunset zones
Question: I’m confused about climate zones. Sunset garden books give the Willamette Valley a different number than USDA gives. Please explain.
Answer: Good question. This is the time of year — garden planning and plant ordering season — to understand and know your climate zones.
USDA Hardiness Zones are based on minimum winter temperatures. Salem is listed as 8b. But the most widely used system in the west, the “Sunset Western Garden Book” zone system, is based upon several variables. In addition to temperature, the “Sunset” zones also account for latitude, elevation, ocean influence, continental air influence and terrain such as mountains and hills. Its maps divide the Willamette Valley into microclimates. Most of the Willamette Valley is in Sunset’s zone 6. A third system you might run into is the American Horticultural Society’s heat zones, based upon the average number of days per year with hot temperatures in any given area.
USDA’s Hardiness Zone Map is based solely on minimum winter temperatures. To me and many others, the USDA system tends to oversimplify the complexity of plant requirements. Based upon minimum winter temperature, the USDA classifies the Olympic rain forest into the same zone as parts of the Sonoran Desert.
Extreme low temperature is probably the single most important determinant of where a perennial can be grown, so the USDA’s system is widely used. If a plant can’t survive the winter because the temperatures normally drop below its ability to harden, then nothing else about the climate really matters. You can find your USDA plant hardiness zone by your zip code at planthardiness.ars.usda.gov/PHZMWeb.
Keep in mind that the USDA hardiness zone map is based on average low winter temperature. So in any particular year, it is possible the temperature might drop to far lower than the average. As well, the USDA’s system doesn’t account for the timing of low temperature events. For example, apricots don’t produce well in Oregon west of the Cascades because although they can survive the winter, they bloom too early in the spring and the flowers suffer freezing injury. Just because a plant can survive the winters in an area does not mean it will thrive there year round. High temperatures during the summer also are a crucial factor in whether a particular variety of plant survives in a particular area.
The USDA Hardiness Zones were updated in 2012 to reflect more years of recent data. The new map is generally one 5-degree Fahrenheit half-zone warmer than the previous map throughout much of the United States. Climate change seems to be showing up with this mapping system.
Before you shop for landscape plants this spring, make note of your microclimate and adjust a “Sunset” zone up or down accordingly. For example, if you live in a hilly area or valley bottom, temperature can be a few degrees cooler than surrounding areas. Your growing season may be a couple of weeks shorter. Plants that thrive in a friend’s garden on a south-facing slope over the hill may struggle and fade in your narrow valley on the north side of the same ridge. And know your USDA hardiness zone. This will help you make the best choices when buying perennials.
Prune fruit and nut trees in early spring
Q: When is it time to prune apple, pears, plums etc?
A: February is a optimal time to prune many of our fruit and nut trees. You have a window of time between the last hard freeze and bloom time. This may last into April.
The Oregon State University Extension Service has a guide, online or in print, “Training and Pruning Your Home Orchard” (PNW 400), that will help home gardeners learn how to prune and train fruit trees the right way. This 16-page illustrated guide explains the basic principles of training and pruning apple, pear, sweet and sour cherries, peach, prune, plum, walnut, filbert and apricot trees. Find it at catalog.extension.oregonstate.edu/pnw400.
Training fruit and nut trees helps to develop a stronger tree that can support heavy crops without limb breakage. It also can help bring a young tree into production at an early age.
There are so many benefits of pruning. Regular pruning helps keep trees at a manageable size, making them easier to maintain and harvest and may increase fruit production and quality. You can eliminate the need for propping up fruit-laden branches by pruning properly. The structural strength and branching patterns can be improved in young trees with good pruning techniques. Good pruning also promotes good air circulation, which helps decrease the spread of fungal and other airborne diseases.
Carol Savonen is a naturalist and writer. She is an associate professor emeritus at OSU and tends a large garden in the Coast Range Hills west of Philomath with her husband and dogs. She can be reached at [email protected] orc/o: EESC, 422 Kerr Admin. Bldg., OSU, Corvallis, OR 97331.
Eugene’s Growing Zone: 6
Our records indicate the United States Department of Agriculture has given Eugene a growing zone designation of 6. Sometimes called the planting zone, this rating gives you an idea of what plants can and cannot grow in the area’s climate. If you are looking for indoor/outdoor plants suitable for growing in the area, head on over to our page on plants that grow well in Oregon.
The USDA growing zone is 6 in Eugene. Understanding your growing zone is very important because it is a measure of the lowest temperature that a plant can survive, helping you to decide what plants would grow best in your particular climate. Since Eugene is in growing zone 6 this means that plants there can survives temperatures as low as -9 degrees Fahrenheit. Plants chosen for Eugene’s climate should be chosen with this in mind or plants should be moved inside to keep their core temperature in the right range if necessary.
Land Area: 9.06 square miles
USDA Growing Zone: 6
Look up average dates for the first frost at the NOAA Satellite Service
Browse Plants By State
Oregon’s stake in $6 trillion prospect
With low national unemployment and a recordbreaking stock market, it might surprise you to hear that new business formation is at a nearly 40-year low. Nationally we’re seeing fewer local businesses and a declining number of startups during this economic recovery.
Sean Parker, formerly of Napster and Facebook, and the U.S. Congress have joined forces to create a new tax incentive program that might just re-energize America’s entrepreneurial spirit. Investors across America are starting to take notice.
The new program is called the Investing in Opportunity Act, which aims to attract capital investments into distressed communities dubbed Opportunity Zones.
Opportunity Zones are census tracts with a poverty rate of 20 percent or higher and a median household income that is less than 80 percent of the surrounding area. Oregon has 86 of these newly designated zones, and five of them are in the Eugene-Springfield area.
“The hope is to spur both economic development and job creation. The investments made in distressed census tracts (Opportunity Zones) will have the potential to turn key community areas around that have historically endured economic hardship to vibrant buildings and jobs that support the community,” says Erik C. Parrish of the local accounting firm Kernutt Stokes.
The Opportunity Zones program creates a trifecta incentive for investors to reinvest unrealized capital gains into funds in exchange for a temporary tax deferral, a reduction in the original amount of capital gains tax, and a tax exemption on any additional capital gains earned on the new investments. There is an estimated $6 trillion in unrealized capital gains sitting on the sidelines in stocks and mutual funds — this creates an incentive to roll those holdings into investments in distressed communities.
Investment options will expand
Opportunity Funds will have freedom to invest in a variety of ventures, including housing, commercial real estate, manufacturing and new startup companies.
What could these investments look like in domestic emerging markets such as Eugene-Springfield?
“Leveraged effectively, Opportunity Zones can expand access to technology innovation and place-based investment in a wide variety of regions throughout Oregon,” says Skip Newberry, president of Technology Association of Oregon (TAO).
Opportunity Funds will be able to deploy investment capital into businesses located in Opportunity Zones. This could include a startup company coming out of the RAIN Eugene business accelerator, or an existing business that needs investment capital to grow.
Opportunity Funds also will be able to invest in real-estate development. The changes to the tax code are likely to make it more desirable to invest in new housing or office space in distressed parts of the community. There has been no new construction in downtown Eugene for many years because it has not “penciled out.” That may change as Opportunity Funds seek investment opportunities.
It is possible that Opportunity Funds will help real estate developers finance projects that also achieve broader economic development goals, such as subsidized space for startups and programs that foster innovation. The decommissioned EWEB Steam Plant is in an Opportunity Zone, and that space has the potential to be redeveloped into a new use that could catalyze innovation in the community.
Springfield holds its own promise
Two of the local Opportunity Zones are in Springfield — Glenwood, a riverfront community between Eugene and Springfield but which is annexed in Springfield, and downtown Springfield, a re-emerging diverse hub for food, microbreweries and creative entrepreneurs.
“These Springfield neighborhoods have a clear vision and community commitment, but at times lack only the final layers of investment to turn vision into built projects. We’re encouraged by the opportunity this program might be, connecting valued investment to an energized community,” says Courtney Griesel, economic development director for the city of Springfield.
Ultimately capital will flow to the investment with the greatest return. The Investing in Opportunity Act does not change the inherent risk of any investment, and new investments may not end up anywhere in Oregon. States such as Ohio already are mobilizing to provide additional complementary state-level incentives to attract capital and maximize the impact of investing in their Opportunity Zones.
Those communities that are successful in attracting capital could see significant job growth and associated payroll and property-tax revenues for community investment.
Lane County’s economic development professionals should work together to raise awareness of our local Opportunity Zones and the investment opportunities in them. State officials should consider complementary incentives to help Oregon be competitive in capital recruitment and to maximize the impact of Opportunity funds, enhancing the startup ecosystem and targeting social benefits.
If only a fraction of that $6 trillion in unrealized capital gains flows into Opportunity Zones, this new program quickly will become one of the largest federal community development initiatives in U.S. history. Oregon’s success comes down to the vision of its leaders and the community’s ability to realize this opportunity.
Matt Sayre is vice president of the Technology Association of Oregon. He lives in Springfield.
Oregon Planting Zones – USDA Map Of Oregon Growing Zones
Gardening in Oregon – Flower, Shrub and Tree Planting with the USDA Plant Map
Gardeners, especially those new to the hobby, want nothing more than to see their flowers, shrubs and trees thrive. Sometimes choosing plants can be overwhelming, as there are some many varieties from which to select. While many factors come into play when considering the suitability of a particular plant, the Oregon USDA plant hardiness information should always be considered first.
Above is the new USDA plant hardiness map, which was just released at the beginning of 2012. The new map divides the country into growing zones based on 10-degree F. intervals according to weather data collected over a thirty-year period. This weather data recorded the average extreme winter low temperatures for the country. Oregon zones are expansive and include zones 4b through 9b. The southern coastal region is the warmest and winter extreme lows are 30 degrees F., while the coolest regions in the state may dip to -20 degrees F.
To find which Oregon zone you are in, you can enlarge the map above. If you want detailed information or cannot find your location on the map, you can visit the USDA site where you can input your zip code to find your zone.
In the Sunset Western Garden Book (2015), Sunset Pub. Corp., Menlo Park, Calif.), the western U.S. is divided into a large number of Climate Zones. These Climate Zones do NOT correspond to the USDA Hardiness Zones. Sunset’s Climate Zones are based on winter minimum temperatures, but also include other factors such as summer high temperatures, length of growing season, humidity, and rainfall. This approach is used to avoid the difficulties encountered when the USDA Hardiness Zones are applied to parts of the western U.S. For example, with the USDA Hardiness Zones, the Olympic rain forest in Washington State is in the same USDA Hardiness Zone, Zone 8, as part of Arizona’s Sonora Desert.
Below are the Sunset Climate Zones used to cover Oregon, Washington, and Idaho. (See the Sunset Climate Zones website for climate maps and more details.)
Sunset ZONE 1A: Coldest mountain and intermountain areas of the contiguous states
Marked by a short growing season and relatively mild summer temperatures, Zone 1A includes the coldest regions west of the Rockies, excluding Alaska, and a few patches of cold country east of the Great Divide. The mild days and chilly nights during the growing season extend the bloom of summer perennials. Winter lows average in the 0 to 11°F (–18 to –12°C) range; extremes range from –25 to –50°F (–32 to –46°C). The growing season is 50 to 100 days.
Sunset ZONE 2A: Cold mountain and intermountain areas
Another snowy winter climate, Zone 2A covers several regions that are considered mild compared with surrounding climates. You’ll find this zone stretched over Colorado’s northeastern plains, a bit of it along the Western Slope and Front Range of the Rockies, as well as mild parts of river drainages like those of the Snake, Okanogan, and the Columbia. It also shows up in western Montana and Nevada and in mountain areas of the Southwest. This is the coldest zone in which sweet cherries and many apples grow. Winter temperatures here usually hover between 10 and 20°F (–12 to –7°C) at night, with drops between –20 and –30°F (–29 and –34°C) every few years.When temperatures drop below that, orchardists can lose even their trees. The growing season is 100 to 150 days.
Sunset ZONE 2B: Warmer-summer intermountain climate
This is a zone that offers a good balance of long, warm summers and chilly winters, making it an excellent climate zone for commercial fruit growing. That’s why you’ll find orchards in this zone in almost every state in the West. You’ll also find this warm-summer, snowy-winter climate along Colorado’s Western Slope and mild parts of the Front Range and in mild parts of the Columbia and Snake River basins. Winter temperatures are milder than in neighboring Zone 2a, minimums averaging from 12 to 22°F (–11 to –6°C),with extremes in the –10 to –20°F (–23 to –29°C) range.
Sunset ZONE 3B: Mildest areas of intermountain climates
Zone 3b is much like Zone 3a, but with slightly milder winter averages of 19 to 29°F (–7 to –2°C) and extremes that usually bottom out between –2 and –15°F (–19 to –26°C). Summer temperatures are a bit higher than in Zone 3a—mostly in the high 80s and low- to mid-90s. Zone 3b offers one of the longest growing seasons of the intermountain climates. Most of it lies in the warmest parts of eastern Washington’s Columbia Basin, with bits in Lewiston, Idaho, and parts of the Southwest.
Sunset ZONE 4: Cold-winter areas of the north coast and mild-winter areas of Alaska and British Columbia
One of the West’s most narrow, linear climates, Zone 4 runs from high in the coastal mountains of Northern California to southeastern Alaska, losing elevation as it moves north. It gets considerable influence from the Pacific Ocean, but also from the continental air mass, higher elevation, or both. As it extends north, the zone first touches salt water in northern Puget Sound and is almost entirely surrounded by salt water in southeastern Alaska. In the contiguous states, Zone 4 has more cold than neighboring Zone 5, more snow, and a shorter growing season. Average winter lows in Zone 4 range from 34°F (1°C) down to 28°F (–2°C),with extreme lows averaging 8 to 0°F (–13 to –18°C).
Sunset ZONE 5: Marine influence along the Northwest coast, Puget Sound, and South Vancouver Island
Mild ocean air moderates Zone 5, allowing it to produce some of the finest rhododendrons, Japanese maples, and rock garden plants anywhere. Summer highs run between 65 and 70°F (18 and 21°C) along the coast, and between 70 and 75°F (21 and 24°C) inland and around Puget Sound. Average January minimum temperatures range from 33 to 41°F (1 to 5°C),with annual lows averaging a few degrees colder, and 10-year extremes ranging from 20 to 6°F (–7 to –14°C).
Sunset ZONE 6: The Willamette and Columbia River Valleys
Warmer summers and cooler winters distinguish Zone 6 from coastal Zone 5. Tucked between the Coast Range and the Cascades, Zone 6 includes the Willamette Valley in Oregon, the Columbia River Valley between Vancouver and Longview, and the Cowlitz drainage from Longview to Toledo.
The Coast Range buffers the impact of Pacific storms, but Zone 6 is still a maritime climate, with a long growing season (from 155 days at Cottage Grove to 280 days in Portland neighborhoods) and 40 to 55 inches of annual precipitation most places. The continental influence is felt two to four times each winter when chilly interior air flows west through the Columbia Gorge and produces wind and freezing rain clear to the Portland airport. Summer temperatures in Zone 6 average 10 to 15°F (5 to 8°C) higher than those along the coast, while winters are cold enough to trigger good fruit set. Ten-year extremes average 0 to 10°F (–18 to –12°C).
Sunset ZONE 7: Oregon’s Rogue River Valley, and Southern California mountains
Zone 7 encompasses several thousand square miles west of the Sierra Nevada and Cascade ranges, and in the mountains that separate the Southern California coast from interior deserts. Because of the influence of latitude, this climate lies mostly at low elevations in Oregon’s Rogue Valley, middle elevations around California’s Central Valley, and at middle to higher elevations farther south. Hot summers and mild but pronounced winters give Zone 7 sharply defined seasons without severe winter cold or enervating humidity. At weather-recording stations in Zone 7, typical winter lows range from 35 to 26°F (2 to –3°C),with record lows averaging from 18 to -0° F (–8 to –18°C).
Sunset ZONE 17: Marine effects in Southern Oregon, Northern and Central California
The climate in this zone features mild, wet, almost frostless winters and cool summers with frequent fog or wind. On most days and in most places, the fog tends to come in high and fast, creating a cooling and humidifying blanket between the sun and the earth, reducing the intensity of the light and sunshine. In a 20-year period, the lowest winter temperatures in Zone 17 ranged from 36 to 23°F (2 to –5°C). The lowest temperatures on record range from 30 to 20°F (–1 to –7°C). Of further interest in this heat-starved climate are the highs of summer, normally in the 60 to 75°F (16 to 24°C) range. The average highest temperature in Zone 17 is 97°F (36°C).
Gardening in the Pacific Northwest Region
The Pacific Northwest region typically includes the states of Oregon, Washington as well as Northern California. From a climate standpoint, in relation to gardening, the Pacific Northwest region has been extended by the National Gardening Association to also include southern British Columbia of Canada.
According to this map of the Pacific Northwest, the region lies in USDA Plant Hardiness Zones 7 through 9 and in AHS Heat Zones 1 through 6. Stretching over a long expanse of territory, the Pacific Northwest climate is influenced by the Pacific Ocean and the Cascade Mountains. Generally speaking, this region enjoys 2 main distinct seasons characterized by mild but very wet winters, cool but very dry summers.
The frost free growing season covers approximately 200 days with the last frost dates ranging from mid-April and the first frost dates starting about mid November. Gardeners in this region are able to grow more perennial varieties than gardeners in any other parts of North America. In fact, this region is famous for its abundant production of tulips, daffodils, dahlias, garden lilies and many more perennial plants. Some plants grown as annual plants in other parts of the country (e.g. Iceland poppies or carnations), will happily overwinter in the Pacific Northwest and re-bloom the following year. An Eden for plants!
However, carefully selecting plants suited to the Pacific Northwest climate will be a key step to success. Plants will have to be drought tolerant in order to cope with the summer months with little or no rain. They will also have to survive the regular cold rainfall in winter and should be resistant to fungal diseases (as a result of the high humidity).
Review our detailed plant selection guides for the Pacific Norwest region and find the best bulbs, perennials, shrubs, ornamental grasses or trees for your garden.
Alternatively, find exciting garden ideas for your geographic area.
Can I Plant a Palm Tree in Portland?
Sometimes we get called to a house where the homeowner is afraid for an ailing tree, then when we show up, guess what? They want to know if they can plant a palm tree as a replacement tree in Oregon and wonder how to keep it alive. People in Portland, listen up – unless you are a horticulturist or arborist, don’t attempt to plant a palm tree in your yard! It will not ever be like the palm trees in sunny California, the main reason? This is NOT “sunny” California. So what can you plant? Here’s how to know – it’s something called hardiness zones.
What are Plant Hardiness Zones?
Plant Hardiness Zone Maps were created by the USDA (United States Department of Agriculture) to help all growers determine what plants will flourish in their area. Here is what the full map of the United States looks like.
Technically speaking, the map maps out zones based on average temperatures for the area. All landscaping zones are divided by 10 degrees Fahrenheit. The zones are based on average temperatures over the past 30 years and do not reflect the coldest temperatures ever recorded or account for the coldest possible temperature in the future. It is important for growers to consider this when choosing plants or trees, like palm trees that are not rated specifically for their landscaping zone. If you are new to gardening, we always recommend staying with plants and trees recommended for your landscapezone. Here’s what the map for our state of Oregon looks like. For those of us situated around the Portland area, we fall within the 8B landscape zone, or plant hardiness zone.
What are Microclimates?
Microclimates are smaller areas that have fine-scale climate variations. For example, microclimates may appear around blacktop, concrete, or small hills that can cause cool spots in your yard. Every yard or landscape is different, and it is important to note any microclimates you may have on your property. Likewise, it is possible that your entire yard could be part of a microclimate. This happens most often when a yard is very sheltered or very exposed. There are a few other factors that can change a gardener’s idea of what they should or should not plant.
Other Factors to Consider When Choosing Plants or Trees
- Light – It is important for plants and trees to receive the ideal amount of sun. The amount of sun an area in your yard receives can vary greatly between summer and winter depending on your area and the amount of shade. Consider what temperature variances can happen in both the summer and winter in accordance with the possible amount of sun before choosing to plant something on the fringe of your hardiness zone.
- Soil moisture – This is usually not a problem in Oregon, but occasionally soil with too little moisture can affect how well a plant or tree does in a particular zone.
- Temperature – Look for the optimal temperature range for a specific plant. While some plants can handle varying temperatures, others cannot. Before you plant, know what temperatures a specific plant or tree can handle.
- Humidity – High relative humidity limits cold damage by limiting moisture loss from sensitive parts of the plant (leaves, branches, and buds). Cold injury can be more severe if the humidity is low, especially for popular in Oregon, evergreens.
So Palm Trees are a Bad Idea, What Can I Plant?
Don’t think keeping it to your hardiness zone means you are limited in choices. The Portland, Oregon area is known for supporting a vast array of trees and plants. Some tree ideas? Maple, Japanese Maple, Hazelnut, Oak, Cherry, and loads of pine trees. If you need help selecting trees for your yard, read our previous post, Choose the Right Tree – Tips from a Certified Arborist, or give us a call! We are happy to help customers learn about trees, and hope to hear from you soon.
Creative Commons Flickr photo courtesy of USDAgov
By Julie Christensen
Trees, shrubs and perennials form the backbone of most gardens, and these plants are also typically the most costly. Because of their slow growth and initial cost, you expect them to last and perform well for many years.
How well plants perform, though, depends partly on the care you give them, and partly on their adaptability to your growing conditions. The closer you can match the plants’ needs to the conditions that are naturally present in your garden, the healthier plants will be with the least amount of effort.
USDA Planting Zones
One tool for choosing plants wisely is the United States Department of Agriculture plant hardiness zone map. This map is based on the average minimum winter temperatures of areas throughout the United States. Each zone is divided based on -10 degree variances. For example, the minimum temperatures for planting zone 5 range from -20 to -10. Minimum temperatures for planting zone 10 range from 30 to 40 degrees.
The plant hardiness zones don’t apply to annual flowers and vegetables because these plants are discarded at season end. Knowing your zone, though, can help you determine which perennials, trees and shrubs are likely to survive in your climate. Plants at nurseries and garden centers are labeled with their hardiness zones. Catalogs and garden books and magazines also use planting zones to aid gardeners.
The USDA planting zones is a helpful tool, but keep in mind that it has limitations. It measures only the average minimum temperature, but doesn’t take into account altitude or humidity levels. Areas that have the same minimum winter temperature might be vastly different in other ways. Consider, for example, Austin, Texas and Portland, Oregon, both of which fall in planting zone 8. These two areas are about as different as can be in terms of summer temperatures and growing conditions.
Just because a plant grows in your planting zone doesn’t mean it will grow well in your yard. Consider how much water the plant needs. What is its native habitat? Does it tolerate wind, wet soil or drought? The cactus that thrives in Austin, Texas won’t do well in Portland, Oregon, even though both cities are in zone 8. One of the most accurate ways to determine if something will grow in your yard is simply to look around and see how common it is in your area. The plants that are used frequently in home and commercial landscapes are those that are adapted to your climate and need the least care. This doesn’t mean you can’t plant a more exotic variety, but it will probably need more attention to thrive.
Consider also, the microclimates of your yard. If you live in an urban or suburban area with lots of trees and pavement, your yard will stay warmer than that of a friend who lives in a rural area just five miles away. Rural areas stay cooler and are usually windier because there’s less pavement to trap heat and fewer homes and trees to act as wind blocks. Within your own yard, you have areas that stay warmer than others. Garden areas with a southern or western exposure are warmer than those on the northern or eastern side of your home. Areas near your home or a rock patio also tend to stay warmer. Sloped areas stay warmer than low-lying valleys, where frost pockets tend to linger.
To ensure plants that are predictably winter hardy in your area, try choosing plants that are rated as hardy one zone lower than your zone. If you live in zone 4, especially if you live in an exposed or rural location, choose plants that are hardy to zone 3. Plant questionably hardy plants in a protected area of your yard and mulch them to help regulate soil temperatures.
For more information on the USDA planting zones map, visit the following links:
USDA Plant Hardiness Map from the U.S. Department of Agriculture
Understanding the New USDA Plant Hardiness Zone Map from Greenhorn Gardening at You Tube
Julie Christensen learned about gardening on her grandfather’s farm and mother’s vegetable garden in southern Idaho. Today, she lives and gardens on the high plains of Colorado. When she’s not digging in the dirt, Julie writes about food, education, parenting and gardening.
By Michael-Anne Foley, Butte County Master Gardener, May 17, 2013
The two primary climate zone maps used in the United States are the USDA plant hardiness zones and the Sunset zone guide. Most (but not all) mail-order plant catalogs indicate the appropriate USDA zones for their plants, while many nurseries in the West use the Sunset system. Since nurseries often source at least some of their plants from big commercial growers, at the same nursery you might find some plants labeled with their USDA hardiness zones, and others labeled with their Sunset zones. It is not surprising, then, that people often find the whole subject of plant-appropriate climate zones confusing.
The USDA plant hardiness map divides North America into 11 hardiness zones. Zone 1 is the coldest; zone 11 is the warmest. When you order plants from catalogs or read general garden books, you need to know your USDA zone in order to be able to interpret references correctly.
The 2012 USDA Plant Hardiness Zone Map compiled by the USDA and Oregon State University is based on the annual average minimum winter temperature over a 30-year period, and is divided into zones of 10 degrees each, further sub-divided into “a” and “b” zones of 5 degrees. Since 1990, the zone boundaries have shifted in many areas. Zones on this new 2012 map are generally 5 degrees Fahrenheit (a half zone) warmer than those indicated on the previous map. This data was accumulated over the 30-year period before 2005; the new zone map based on this information was released in January of 2012.
Now, for the first time, the USDA map is available as an interactive GIS-based map, for which a broadband Internet connection is recommended, and also as static images for those with slower Internet access. Users may also simply type in a ZIP Code and find the hardiness zone for that area. For example, using the USDA Hardiness Zone map, Chico, Oroville and Paradise are all located within Zone 9a (minimum winter temperatures of 20-25 degrees Fahrenheit). Although this is a useful plant hardiness index it has some important drawbacks: for example, it puts the Olympic rain forest into a zone with parts of the Sonoran Desert.
Gardeners in the western United States are sometimes confused when confronted with these 11 Hardiness Zones created by the USDA. A more useful index is the 24-zone climate system published in the Sunset Western Garden Book in collaboration with the University of California. The Sunset climate zone map for gardening was devised in the mid-20th century for thirteen western states. It has been expanded to include areas across the U.S., providing a more useful alternative to the USDA zone system.
The 24 Sunset Zones are determined by a number of factors to help gardeners identify the most appropriate plants for their needs. Winter and summer highs and lows are used to provide information about the temperature extremes in the region. Weather patterns like humidity, rainfall and heat are considered. The Sunset Zones also take into account specific environmental conditions like prevailing winds, day length and soil type.
The greater precision of the Sunset system is evident in our local area: Chico is in Sunset zone 8, Paradise is in Sunset zone 7, and Oroville is in Sunset zone 9. Because the Sunset zone maps are more precise than the USDA’s, they are considered the standard references for gardeners in the West. So, when you purchase plants for your zone, be sure you are using the right zone map! Sunset’s zones 7 and 8 are much warmer than the USDA zones 7 and 8; mixing up the systems might well result in planting the wrong plant in the wrong place.
And keep in mind that even within a city, a neighborhood, or a street, microclimates can affect how plants grow. For example, planting tender citrus against a wall that absorbs daytime heat places it in a micro-climate that is warmer than a more exposed area. The zones are a guide and a good starting point, but you still need to determine for yourself what will and won’t work in your garden.