The Facts in a Changing Climate

I recently did a talk at the Yard, Garden, and Patio Show in Portland, entitled ‘Plants for a Changing Climate’.  Some shared interest that I post my talk so I will describe it in this blog and I hope you find it informative. The first half of the talk was describing the weather over the past 60 years. The second half was plants. I’ll just be talking about the weather here. I’ll try to keep it as cut and dried as possible- I won’t veer off though I have a habit of that. Heh.

The Record

There are many ways to approach the climate over time. And I won’t bore you with intricacies but I will show how I arrived at my information. To be simple and precise I chose to compare our extreme temperatures as a way of showing change.  I won’t be focusing on monthly averages or even yearly day to day averages. To make it more comparable, this is how the USDA arrives at their zones so it seemed appropriate. The weather record in Portland is not exactly as long as you would think so I used two records to make up for that. The official record at Portland International Airport only extends as far back as October, 1940. Thats when the airport was moved from Swan Island to its current location. Why there isn’t a published record on Swan Island, I don’t really know, but I have seen it mentioned in old literature. The second record which extends back to 1875 is that of downtown Portland. I’ll talk about why that is useful but also limited. Be aware that these two records are urban- well not as much the airport but they are our official records and there is quite a bit of difference between them and the suburbs. I’ll also review the distinct microclimates in the metro area.

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20ºF, 100ºF- Life above and below

In my search through records I had to delineate certain temperatures to make it more simple. For instance, I chose 20º above (zone 9) and 20ºF and below (zone 8 and colder) and that was fortuitous. Think of zone 8 as the line we cross into what we consider arctic air in our region. It turns out that is exactly how our winters fall, to give away a simple fact our average annual low at the Portland Airport in the last 30 years is 20.3ºF (-6.9ºC). And our winters have a distinct percentage above and below that line. This is arbitrary, I know but it really works for our discussion. Also, I reviewed our annual highest temperature and would you believe that is exactly 100.0ºF for the past thirty years? Tracking the ultimate high might mean less to gardeners than freezing temperatures, but I wanted to see if that foretold a trend in extremes as well.

30 Year average

The official USDA zone maps are compiled by averaging the yearly low temperature extremes at official reporting stations. This is done in 30 year increments and the last thirty year review was 1980-2010. In my review I chose to look at 1986 to 2015 in order to see if there had been any more change in a more modern appraisal. The information is there so, hell, why not? The official temperatures at official reporting stations are compiled and then isothermic lines are drawn to delineate the zones in the region. For instance, in the Portland Metro area those official reporting stations are: Pearson Airport- Vancouver, Scappoose Airfield, Hillsboro Airport, Portland International Airport, Troutdale Airport and Aurora Regional Airport. Those 6 stations are relevant to our immediate area. By the way if you look at our current observations page at the NOAA website those are what come up and those are the only stations with official records. Of course there is a significant amount of difference between each station. Topography, elevation, exposure to the Columbia River Gorge and distance from it all play into the local climate.

Microclimates: Macro differences

Microclimates in our region are distinct in several different ways. First, elevation has several effects. You might think that the higher you are the colder you are, well thats only partially true. Honestly, cold air sinks and the most extreme cold temperatures in our area are recorded at the lowest elevations. Once you get above about 700′ the temperature again begins to drop. So, slopes between 700′ and about 200′ in the metro area (and Willamette Valley) are considered thermal belts. If thats difficult to picture just remember that is where you see wine grapes grown in our region- there they avoid late and early valley frosts and the cold air sweeps downhill and does not collect. The most important aspect of elevation in western Oregon is that the higher you are the wetter you are. Elevation is the key. The Portland Airport at 21′ above sea level records the least amount of rain in the metro area at 35.10″ annually. In the west hills of Portland above 800′ that average spikes up to 55″ and more. As far as precipitation is considered elevation is everything. By the way downtown Portland at 110′ elevation averages 42.30″- so you can see how sensitive that is. A few feet and wow. Also, there is much more snow at higher elevations and this increases even more dramatically.


The longest records and what they tell us

The longest record of Downtown Portland- taken at the KGW Television Station currently tells us a lot about the trajectory of our climate. Computing the averages 30 years at a time from 1875 until 1955 and guess what? Our climate was colder. There were warm years and very cold years.  What is interesting about this time frame is two striking things. First the 19th Century was very much colder than the 20th century- we were exiting the Little Ice Age which ended in approximately 1910- most likely that was caused by what is known as the Maunder Minimum a period of less sun spot activity and some pretty honking big volcanic eruptions (Tambora 1815) contributed to significant cooling. Then in the late 18th Century the industrial revolution began spewing CO2 into the atmosphere and sun spot activity changed. A combination of the two shows a turn in climate. And you can see a change. An example that shows warming sensitivity is average annual snowfall. In 1900 downtown Portland averaged 18.1″ of snow per year. Thats an awful lot. Currently, we only total an average of 3.1″.  Also, there were regularly widespread regional arctic outbreaks that lasted for weeks at a time. In fact the Columbia River and the Willamette both froze over regularly. That speaks not just of intensity but duration of freezes. The last record of both rivers freezing completely is 1933. Also, exceeding 100ºF, rare in the 19th Century became much more frequent following 1910. This is a trend that has repeated all over the west so we know some sort of transition was taking place. Just for fun there was only one year that never dropped below freezing, that was 1934- and as you know from history the 1930’s showed great perturbation in climate- not just the dust bowl but in the PNW as well.

The Ultimate Extremes

I chose the last two thirty year increments to really delve into details. And before that just how cold was it? Downtown Portland’s coldest temperature officially was -2ºF in January 1888- a month that saw more than three feet of snow- something unfathomable now. At the Portland Airport the coldest temperature was -3ºF in early February 1950- a winter of intense cold and and snow. In an aside the coldest temperature recorded that winter  night in downtown Portland was a relatively warm 7ºF- remember microclimates are everything. It could be that by that time the urban heat island was beginning to emerge. The urban heat island is just that- an area like an island in urban cores where glass and asphalt absorb heat and then release it gradually.  It becomes very apparent in averages.  Surprisingly the warmest temperature prior to 1955 downtown was 107ºF in 1942 a high that hasn’t been achieved since.

1956-2015- Downtown Colder then…

To really get a handle on our climate I chose the last two 30 year increments to see if that showed valuable change. I figured the last 60 years is about relevant to the older plants in gardens (heh). And what I discovered was not a huge surprise. In 1956 to 85, downtown Portland had an average annual low of 19.3ºF- Zone 8b. There was just one winter below 10ºF (Zone 7) 6ºF in 1968. 13/30 winters were Zone 8 or colder and that averages out to 43.33% in that time frame. Conversely, 17/30 winters were above 20ºF- or 56.66%. Now, this is in the urban core so it is only surprising in that it is way warmer than most people would surmise. The warmest winter was the El Nino year of 1958 where the lowest temperature was a paltry 31ºF. Barely a frost. The average annual high was 99ºF with an ultimate high of 106ºF in the great heatwave of August 1981.  In 1985 to the present the downtown recording station showed slight warming. In that time the average annual low rose to 22.3ºF (Zone 9a) and zone 9 winters increased slightly to 60% of average. The highest temperature remained stagnant and the highest recorded temperature was 105ºF in July, 2009.

1956-2015  Volatile weather at the Airport

The average low temperature at PDX in period 1956-85 was exactly 15ºF (Zone 8a). There were 21/30 years in those 30 years with winters zone 8 or colder. (70% of winters). Five of those winters were zone 7 (10ºF) or colder with ultimate lows of 6ºF in 1957 and 1964. Just 9 winters were zone 9. What is striking is that in the last 30 years the percentages have reversed. Fully, 56.66% (17/30) winters were were zone 9. and just 43.33% of winters of zone 8 or colder. The most striking statistic is that the coldest and last official zone 7 freeze at PDX was February, 1989 with a low of 9ºF (a particularly brutal freeze with highs in the teens for 3 days). Thats 27(!) years since a true zone 7 winter.  Something has changed. Nothing like that expanse of time shows up anywhere in the previous records. The highest temperature was 107ºF in 1965 and again during the phenomenal heat wave of August 1981 where 107ºF occurred twice in one week. So, the average annual low- as I said rose to the current 20.3ºF (Zone 8b)- unless you want to believe we are .3ºF into zone 9. The warmest winters were 1999 and 2002 and where the lowest temperature was just 26ºF.  (This year the lowest was 24ºF and last year it was 23ºF).

Microclimates show much greater extremes.

Those are urban records and I took a look at the records from the other reporting stations and they show quite a bit of difference. In Hillsboro for instance the coldest temperature of 4ºF was achieved in 1989, 1998 and it dropped to 7ºF as recently as December, 2013. Cold air sinks and away from the Columbia Gorge in the Tualatin Valley where there is less air mixing and greater radiational cooling as well, it gets quite a bit colder. This pushes Hillsboro down to Zone 8a (11ºF) and it averages a zone 7 freeze at least twice every ten years.   Another surprisingly cold part of the metro area is Vancouver as well as rural Clark County. Cold air collects and in 2013 the mercury dropped to 7ºF in the last big freeze. This area though officially zone 8a (14ºF) averages one out of ten years with a zone 7 freeze. In both of these locations that should be taken into account when choosing longer lived plants (shrubs, trees).

Our current climate

So, what is our climate like in the 21st Century? And remember that averages are made up of extremes. There will be colder winters as well as warmer winters- that is part of climate. The way it affects gardens is real. And you should always record the temperatures in your own garden- you may live in a frost pocket. Remember that exposure to subfreezing winds (from the Gorge) knocks off a lot of plant hardiness. I like to remember that at 20ºF a 30mph wind causes the equivalent damage to a wind-free 10ºF- thats how zone 8 plants can be damaged or killed at a zone 9 temperature. And gardeners here know that sodden plants can be injured in combination with low temperatures. We can expect one day a year with a high temperature below 32ºF. One day a year with a low below 20ºF, 44 days below freezing, one day a year with a high above 100ºF and 16 days above 90ºF.

The future looks very different

In the last 100 years our temperature in the PNW has risen by 1.3ºC. And you can see that has had a distinct effect. We will continue to warm. 2015 was our warmest year ever, we broke the record for most days above 90ºF (29) most days with highs above 80ºF and most lows above 60ºF, 6 of the 12 months were the warmest on average ever recorded. And the number 2 year? 2014. Its a trend- last year was a glimpse into the future. Experts expect that our climate will warm in the PNW by 3-5ºC by the year 2060. Thats kind of hard to imagine. Snowpack will become more volatile, low elevation snow will likely disappear and water will take on more importance. More than ever we should learn about our climate and prepare.












The Facts in a Changing Climate

Proteaceous Plants for Portlandia

Grevillea miqueliana



One of my favorite groups of plants is the Protea family.  As in Proteas, those immense and gaudy over the top cut flowers that go for $8.00 a pop. And you may say well yes, those grow in Hawaii and they are native to South Africa. Well, the jury is still out on whether we can grow any Proteas here. (There’s progress in that department). But there are others that I dearly love and feel compelled to push on gardeners. The ancient Proteaceae is mostly centered in the Southern Hemisphere and it is from Australia, South America and less so from South Africa-that we can find members that will grow for us.

Specific conditions are not so hard to meet

Right off the bat one thing that you should know about this family is that they are adapted to poor soils. I mean, really shitty stuff- the oldest most worn out soils in the world (Australia) and they have developed certain adaptations to deal with this. Proteoid roots are clusters of dense tiny roots in circular structures that mean to suck the very life from the soil. Along with some microbial activity they are super sensitive. That means that they are susceptible to too many nutrients. They glut and they die. Phosphorus is the one mineral that they have a serious time digesting and to a lesser extent potassium. That means the NPK is pretty much turned upside down for these plants. How do you grow plants that hate fertility? Well, it turns out its a little bit of a trick in pots but in our native  soils its not a problem at all. Just do nothing. Neglect is their friend and I will get back to that.

Cold hardy members of the clan

The trick then is to look for members of this family that can take our cold winters- the vast majority of this family is from mild to subtropical to tropical environs. It turns out that since Australia is a big place and there are mountains and mountain valleys where it gets fairly cold that there are specific regions to choose from. These alpine species that occur in the Australian Alps and the higher Mountains of Tasmania have yielded what I think are some of the coolest shrubs we can grow in Portland and the rest of the west slopes of Cascadia. When I research plants I like to go one genus at a time and look at the whole as we say electorate. I swear that if you use this approach you are almost always bound to find a species that will grow in our favored climate. So lets start with the largest genus in the family. Grevilleas.

Whittling it down

344 species of shrubs, ground covers to grand trees. The vast number of Grevilleas are shrubs and almost 99% are native to Australia. They are shrubs by the way because shrubs are adapted to take less water than trees….see how that works? Then you whittle it down to those from high elevations and and cold pockets. That reduces us substantially down to maybe two dozen. Already this is easier to manage. Remember Australia and Tasmania get cold but nothing like Oregon- not even close. Then you do a little research (well, maybe a lot, maybe obsessively a lot) and you look for regions of the world similar to Portland and you look for species and cultivars that are being grown there. Turns out that some people in some similar regions are not as obsessive as you but that is for another time. Another thing to do is to querie your nursery friends in California and find out which of these made it through their all time coldest weather with no damage. Put these two methods together and you have a group of plants to work with.

California is right down the road

Luckily we are in close proximity to California and it is there where just about every Grevillea there is can be grown. Its that pipeline that has allowed species to stray north and be trialled.  And there is a long history of certain Grevilleas that have been grown here. The problem is they were usually stuffed in the back of Botanical Gardens- isolated or maybe with one or two Australians like they were in a circus freak show- forgotten oddities. This always made me sad and it turns out that they should be dragged from the shadows into our gardens. That time I reckon is now. At Xera I have experimented with a whole group of this genus and I’ve even done a little breeding and seed selection. We aim to get the cold hardiest, easiest to grow and most spectacular varieties out there for gardeners to try.


Grevillea x ‘Neil Bell’

Why do we love them so much?

First of all as a whole they are extremely drought tolerant and they seem to relish our winter wet summer dry climate- with little to no coaxing they thrive. Second, they have the coolest flowers- completely different than  what we are used to and third they bloom almost year round here. They love it, we love it and Hummingbirds find it almost orgasmic. They range incredibly in leaf size and texture. And they make perfect companions to our drought adapted  natives such as Arctostaphylos and Ceanothus- as examples. They require- no, they demand nothing and pay big dividends in return.

A genus made to party

It turns out that Grevilleas are a fecund and promiscuous genus. That is to say that just about everybody crosses with everybody. They know how to party. That means you can get some very different looking plants to cross- unlike many other genus’ with a tighter rein on the gene pool- and the intermediary traits of the very different plants yields a huge range. For instance Grevillea juniperina (Juniper Leaved Spider Flower) with tiny sharp needle foliage can cross with Grevillea victorae- with large entire leaves. The resulting progeny run the gamut in leaf size and flower color. A huge range. One interesting thing that I’ve found is that seedlings from certain plants that are not hardy can actually yield hardy plants. Its a question I do not have the answer to but on more than one occasion I’ve grown plants from seed only to have the parent plant and a good percentage of the offspring freeze and die, while certain seedlings prevail- even sail through undamaged. These plants are planted in ideal conditions just feet apart in the same soil conditions. So that means something else is going on here and it means that you should always test a plant through our coldest weather because you can’t be certain that a seedling will be cold hardy. The reverse is true two cold hardy varieties can yield a tender offspring. So- all should be tested. And through this method we have yielded some exceptional cultivars.

The glory of survival- ignore them

This is information we’ve amassed over the past 15 years. Careful observation and culture. Most importantly you should plant Grevilleas in the warmest possible position in your garden. That is most commonly a south facing slope where cold air can drain by. Warm walls work too but that can inhibit dormancy and lead to problems down the road. So in a HOT position in NATIVE soils. That means do nothing but dig a hole and plant it. I usually give it a cursory watering to settle in the soil but that is it. In my 15 years of growing them here I have yet to see a drought stressed Grevillea. They can be grown in clay soils on slopes if strictly unwatered. They also can benefit from the overhead protection of a tree canopy so long as it is a high canopy that lets in lots of light. If the soil is too fertile you can run into problems with chlorosis and this is the yellowing of new leaves. If this is really a problem you can either spray it with chelated iron or rip it out and try again in another spot. Do not water them. They can be susceptible to phytophthera in wet soils and this can be the kiss of death. DON’T water them. If your Grevillea grows too quickly it may rock, simply stake it up. I usually give mine a good tip pruning in spring too to even out top growth to root mass. Tip pruning will also cause the shrub to bloom. So if you have a big healthy plant that refuses to bloom tip prune it and you may be surprised.

Some other hardy Proteoids

Grevilleas  are not the only Proteoid genus there are many others. A personal favorite are the Tasmanian Hakeas. They look like nothing else we grow. Large shrubs with spikes for leaves.  They are see through shrubs/small trees and two have proven to be perfectly hardy to cold. Hakea microcarpa has blue green upright growing foliage and in early spring in the leaf axils flossy white fragrant flowers crowd the stems. The other is Hakea epiglottis with more grass green spikes and it has small sulfur yellow flowers in spring that smell like cloves. Both grow to 12′ or so and very quickly. Again, never water.

Another genus from Australia that is successful with very pretty shrubs that look incredibly different are the Lomatias. The 3′ to 4′ tall with finely, lacy leaves of Lomatia tinctoria give it the common name guitar plant and it has 1′ tall spikes of ivory white flowers in late spring that remind me of an impressionist painting. Another much different Lomatia is Lomatia myricoides. It has long thin leaves and clusters of clove scented ivory white flowers in summer. Its an upright arching shrub to 9′ tall. It does seem to tolerate irrigation and it has endured temperatures down to 0ºF- not happily but it survived.


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Lomatia tinctoria
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Lomatia myricoides

If you are just beginning with this family here are the easiest and most cold hardy varieties that we have grown.

Grevillea australis   3′ x 5′ wide ochre colored small leaved tiny white flowers that smell of honey in spring. A handsome shrub that has been hardy to just below 0ºF. Easy to grow.

Grevillea victorae- 9′ x 6′ wide its a big shrub that is also a GREAT PLANT PICK. Handsome large grey green foliage and orange flowers nearly year round. It can stand a little shade. Also, tip prune to encourage flowering.

Grevillea x ‘Neil Bell’- This has surprised us and after going through 5ºF without a scratch in several gardens well, you gotta give it credit. To 7′ x 7′ with tomato red flowers year round.

Grevillea  miqueliana – Round leaf Grevillea is the unoriginal common name. Its a big dense shrub for full blasting sun to light shade- it also tolerates clay soils. Its persisted through the coldest winters of the past 15 years. Sunset colored flowers orange/red/yellow are pendulous and once it starts blooming it blooms year round.

Grevillea juniperina ‘Orange Zest’- Our selection of the Juniper Spider Flower with needle like green leaves and masses of bright orange spidery flowers from late winter to late summer. This is one of two survivors of this species that has handled 5ºF twice and with little more than a few brown twigs. To 3′ tall and 7′ wide. Poor soil.

This is just the tip of the iceberg there other species and more that are coming along and many more worth trying- especially if your garden stays consistently above 10ºF- such as urban Portland. We have slowly been expanding our list- through trial and error. And we will be offering them at our shop for intrepid gardeners. Also, another nursery that specializes in Proteaceous plants if you have to order through mail is Desert Northwest in Sequim, WA.. He offers a great variety too with good information on plant hardiness.

As for the weather, this El Nino will go down as one of the wettest for us on record. And after seeing some information on the strongest El Nino’s it appears that they produce a lot of rain for us. Still, there is absolutely no arctic air in the next few weeks so get ready, get set, its time to garden. We will be opening our retail shop on February 4th. Initial hours will be 10 am to 5pm until March. For questions call 503.236.8563.

Thanks, Paul




Proteaceous Plants for Portlandia