Are natives the answer? Revisited

I started to leave a comment on Linda’s Friday post regarding Seattle Public Utilities proposed building codes regarding “Healthy Landscapes” but decided I’d weigh in with a regular post.  Linda honed in on the 75% native requirement but there are lots of things to make one scratch their heads in the proposed codes.

Existing invasive plant species shall be removed and no invasive species planted.
No mention of how invasive plants shall be removed.  Heavy-duty herbicides? Armies of school children forced into slave labor? Slow-moving ground-fire? Goats?

75% of all new plantings will be native to Western Washington.
So where did 75% come from?  Sounds like a number that was pulled out of the air.  How is 75% defined?  75% of plants? 75% of the area?  And how does this foster “Healthy Landscapes”?  If I have a 2 acre landscape and plant an acre and half of salal or Oregon grape I’ve met the requirement of 75% but have I increased species diversity or structural diversity or contributed to a “Healthy Landscape”?

A vegetation plan must be submitted for review.
By whom?  What happens if they (whoever ‘they’ are) don’t like it?

Existing native plant species shall be protected whenever possible.
Sounds reasonable but what about existing non-invasive non-natives?  Could a homeowner be required to cut down a 40-year-old red maple?

And on and on we could go.  Let me state clearly, I’m not against native plants.  Quite the opposite – I grew up in western Washington and have a passion for PNW plants since my high school days.  Since moving to Michigan I’ve written articles and given talks promoting natives here as well.

Nonetheless, I think many in the native plant movement hurt their cause by parroting the same old lines without ever critically thinking about what they’re saying.  Repeating a lie often enough times does not make it the truth.

Let’s critically look at some of the reasons for planting natives according to the Washington State Native Plant Society:

Native plants are adapted to our climate of wet winters and dry summers.
True. But so are lots of non-natives.  Adaptedness is a function of the environment in which plants have evolved; whether it’s native or exotic.  There are many climates around the world that are similar to the PNW and can produce similarly adapted plants.

Require less water than most non-natives once they are established.
Once again, adaptations such as drought tolerance are a function of the climate under which plants evolved.  There are many exotic species that are more drought hardy than western Washington natives and likely to use less water.

Resist native pests and diseases better.
Sometimes. But unfortunately the days of worrying only about native pests are in the distant past.  Exotic pests are here and they are here to stay.  Dutch elm disease, white pine blister rust, emerald ash borer, chestnut blight, Japanese beetle, the list of exotic pests is long and getting longer.  Native does not mean pest-free.

Improve water quality by needing less fertilizer and no pesticides.
OK, here’s where I get confused.  The reasoning in Doug Tallamy’s book, Bringing Nature Home, is that native insects don’t feed on exotic plants, therefore if we plant exotics, native food pyramids will collapse and it will be the end of life as we know it.  So… if native insects won’t feed on exotic plants, why would exotics require more pesticide use?

Save resources and encourage a sense of Stewardship.
Ok, now maybe we’re getting somewhere.  Not sure why stewardship is capitalized here but if they mean a ‘sense of place’ or a ‘connection to the natural environment’ then I can buy it.  Many native activists, including Tallamy, run away from this argument – apparently it doesn’t sound scientific enough – but it’s one of the best we have.  Washington state has some of the most incredible plants anywhere.  They should be celebrated and promoted and planted.  In my mind, the biggest reason for planting natives – along with carefully selected non-natives – is to increase overall biodiversity.  When I mention biodiversity I am speaking broadly; species diversity, structural diversity, age-class diversity, and landscape diversity.  When we look to the future we have no idea what lies ahead. We don’t know what new, exotic diseases or insects are looming on the horizon. Most of us expect climate will change but no one can say with certainty how.  Plants cannot evolve as fast as climate will change or as fast as new pest will be introduced. The only way to deal with this uncertainly is to spread the risk through diversity – this includes natives, exotics, and even interspecific hybrids.

Toxic mulch: When shredded bark goes bad

We typically think of mulching landscape beds as a good thing.  And it usually is; helping to conserve soil moisture, reducing soil temperatures and contributing to soil organic matter.  Recently, however, I received an e-mail from a local landscaper that reported severe damage to annuals and perennials in a landscape bed immediately after applying hardwood mulch.  The problem, sometimes referred to as ‘sour mulch’ or ‘toxic mulch’, occurs when mulch is left is large piles and undergoes anaerobic conditions.  This results in the production of acids and other compounds that can volatilize when the mulch is placed in beds, especially during hot weather.  These vapors can quickly damage annuals and other sensitive plants.  Mulch in this condition is often characterized by a ‘sour’ smell.  If you suspect your mulch has gone sour, spread it out before use to allow toxins to dissipate and water thoroughly either before or immediately after application.  The University of Arkansas Extension has a nice fact sheet in the subject “Plant injury from ‘sour’ wood mulch.

Fried Gerber daisy

Sedums are usually pretty tough…

And, yes, I did steal the title of this post from one of my all-time favorite ‘Far Sides’…


Every survivor has a story

It’s been suggested, not unfairly, that the Garden Professors are sometimes a little ‘Tree-Centric’.  As a forester and tree physiologist by training, I’m probably the guiltiest among my co-conspirators on that count.  But occasionally I do notice things less than 10’ tall and lacking a single, woody trunk.


When weather permits I like to take my lunch down to the MSU annual trial gardens behind my office here at the Plant and Soil Science Building.  Every summer the annual gardens are awash with the color of impatiens, geraniums, petunias, and other annuals.  This time of year, however, it’s bulbs that steal the show.  This spring there was a display of bright pink tulips that was especially striking.  Wandering by the beds recently I noticed a tag in one corner; ‘Susan Komen mix’.  For those that aren’t aware, Susan Komen lost a long, brave battle with breast cancer in 1980. The foundation founded by her sister, Susan G. Komen for the Cure, is the leading advocacy and fundraising group for breast cancer awareness and research in the US.  Komen for the Cure also provides services and advocates for our country’s two and half million breast cancer survivors.

In many ways, tulips are a fitting symbol for breast cancer survivors and the brilliant pink show made me think of a cancer survivor I know, my college girlfriend, Lisa.  I remember learning about her cancer nearly two years ago.  We had followed our own paths after our undergrad days and contact was sporadic as we each set out on careers and started families.  I missed her at our 30th high school reunion but found her number in the reunion directory and rang her up. The words hit like a punch in the stomach, “I underwent breast cancer surgery and treatment this past winter.”  I was stunned but in the next instant knew her trademark grace and humor were still intact.  “Yeah, when the reunion notice came out I had just lost both my boobs and all my hair.  Ya know, I just wasn’t up for all the ‘Hi, how are ya’s?’”  Today, Lisa remains cancer-free though after-effects of radiation treatments linger.  Through the wonder of Facebook we now keep up on each other’s awesome and talented kids.  She’s looking forward to two year’s cancer-free in July and then the all-important 5-year mark beyond that.

So, what does all this have to with landscape horticulture?   My friend and colleague Art Cameron concluded a talk at our Master Gardener College last Saturday with a quote: “To plant a garden is to believe in tomorrow.”  So much of what we in do horticulture is an expression of our faith in the future.  When we plant tulips in the fall we know they must endure dark, cold days each winter in order to bloom the next spring.  Breast cancer survivors and their families have to endure more than their share of darkness to see brighter days. We’ve become a society obsessed with instant gratification and the old cliché ‘stop and smell the roses’ seems trite and shopworn to a lot of folks.  But gardens connect us to the earth and to each other and provide the perfect place to take time and reflect on things that really matter.

According to the American Cancer Society nearly one in eight women in the US will develop invasive breast cancer in their lifetime.  To learn more, read breast cancer survivor stories, and to support breast cancer research go to

Blue Spruce Blues

One of the roles I’ve evolved into over the past decade as an extension specialist at MSU is that of ‘the Conifer Guy’.  Conifers are great and fascinating plants.  The oldest trees in the world are conifers, the largest trees in the world are conifers, and some of the most interesting (at least to me) landscape plants are conifers.  Unfortunately, for a variety of reasons, in the Upper Midwest we have gravitated to Colorado blue spruce more than just about any other conifer.  Part of this over-reliance on blue spruce in the landscape is driven by production (see, Linda, I’m not always an apologist for nurseries).  Growers want to grow what they know and what’s easy to grow.  As a nursery tree, blue spruce is a reliable performer that is well adapted to a relatively wide range of site conditions.  Of course, growers also want to grow what they can sell, and there always seems to be a steady demand for blue spruce.  In many neighborhoods it appears that there is an ordinance that every other tree has to be a blue spruce.  So what’s the issue?  In the Great Lakes region, blue spruce often look pretty good when young.  However, as trees age they become susceptible to several major pests, especially cytospora canker and gall adelgid.  So all those shapely blue Christmas trees that were planted 10 or 15 years ago are now a bunch of ratty-looking messes.  So what’s the solution for blue spruce burn-out?  Clearly landscapers and homeowners need to think beyond blue spruce and look for a greater variety of choices.  Here are three to consider.

– Serbian spruce Picea omorika  Whenever I’m asked to suggest a conifer, Serbian spruce is usually one of the first trees in the conversation.  While the color may not be as striking as a blue spruce, Serbian spruce still has impressive needles in its own right – bi-color with dark green on the upper side and silver below.  Adding to Serbian’s charm is its graceful weeping habit.

– Swiss stone pine Pinus cembra The late, great conifer expert Chub Harper used to remark, “I never met a cembra I didn’t like.”  Chub’s fondness for Swiss stone pine was well founded.  Here is an understated, consistent landscape performer.  Few pests, dark green needles and stately upright form.

– Korean fir Abies koreana  It would be a stretch to consider Korean fir an alternative to blue spruce.  While Korean fir is more broadly adapted than many of its pantywaist cousins in the genus Abies, it will still do best on the Holy Grail of moist, well-drained slightly acidic soils.  Nevertheless, Korean is tougher than the average fir and is a conifer with some character and worth a shot.  Korean firs are often heavy cone producers, which can add an interesting element of color.