Author: Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

Proposed phosphate fertilizer ban

Today I received an email alerting members of Washington Friends of Farms and Forests to a proposed ban on phosphate-containing fertilizers in the state of Washington.  Here’s part of the text of the email (I’ve removed underlining, bolding, highlighting etc. so this reads as objectively as possible):

“Concerns with the HB 1271 & SB 5194 banning the sale of fertilizer containing phosphorous:

1) The intent section contains scientifically inaccurate statements, creating a false precedent that turf fertilizer is a significant surface water pollutant and is not necessary for a healthy lawn.

2) It grants the authority to regulate fertilizer sales and use to the Department of Ecology (Currently, the Department of Agriculture regulates fertilizer content and registers it for sale.)

3) It changes the definition of fertilizer used by the Department of Agriculture, creating confusion.

4) It is inconsistent and will be ineffective because it exempts “natural organic sources.” Organic products are high in phosphorous. The ecosystem cannot tell the difference. All fertilizer should be regulated equally.

5) It fails to recognize the expertise of trained lawn care professionals, who should not be prohibited from providing quality service to their customers, including publicly owned golf courses, parks, and sports fields.

6) As written, it bans the use of phosphorous fertilizer for forestry, house plants, shrub beds, golf courses, sports fields and other uses. It is unclear as to private commercial property.

7) It bans the sale of phosphorous fertilizer for flower and vegetable gardens, forestry, house plants, shrub beds, golf courses, sports fields, and many other uses.

8) It bans retailers, including farm stores and ag dealers, from displaying any type of fertilizer containing phosphorous.

9) It fails to address the primary causes of impaired water quality. Regulating something because it’s easy without addressing root causes of the problem accomplishes nothing.”

So, readers and colleagues, do a little homework over the weekend.  Look at the bill itself (both the house and senate bills are the same; the link is for the house bill).  Are these nine concerns valid?  Discuss.

When trees attack!

I’ve been suffering through my post-holiday, post-annual-reporting cold and/or flu, so I don’t feel as witty (or snarky) as I might otherwise be.  Instead, I feel like my body’s been invaded by a slowly spreading mass that reminds me…oh, I don’t know…of what trees can do when they encounter an immovable object.

Not much of a segue, I know, but I just had the urge to post some interesting photos after Holly’s photo-fest yesterday.  (Memo to self: not fun being Holly’s follow-up act.)  Anyway, you’ve seen what happens when growing trees encounter neglected plant tags:

And perhaps you’ve seen how roots laugh at puny planting pits:

So before you feel the urge to attach something – anything – “permanently” to a tree, keep in mind that they have no respect for authority…

…or even those who got them started in life:

Fast food is unhealthy for plants, too

In early December, I posted my thoughts about fertilizing crops vs. landscapes.  An anonymous reader asked if we could follow up by discussing the relationship between excessive fertilizers and plant susceptibility to pests and disease.  It’s taken a month to get the scientific literature (and my act) together, but here it is.

There are decades’ worth of articles about the direct relationship between increased nutrient availability and increased susceptibility to pests, disease, and disorders.  One of the earliest articles linked the incidence of celery blackheart to over-fertilization.  Since that time, researchers have found similar causal relationships in vegetable crops such as rice, onions, and soybeans, ornamental crops including poppies, and perennial orchard crops such as nectarines.  Unfortunately, there’s been no research on landscape species.

Happily, the way plants react to excess nutrient levels is generic – so we can apply the findings in the agricultural literature to landscape situations.  Just like kids and candy, plants will greedily take up all the available macronutrients their roots can find, especially nitrogen and phosphorus.  (It makes NO difference is the fertilizer is organic or inorganic.)  Plants in highly nutritive soils respond with lush vegetative growth – and fewer flowers, by way.  Less metabolic energy is put into protective compounds, so these succulent new leaves and shoots are prime targets for all kinds of unwanted plant-eaters and foliar pathogens.

As with so many things in life, moderation is the key.  For routine landscape needs, use woody mulches rather than fertilizers and nitrogen-rich composts.  This “slow food” approach not only benefits your plants, but provides ideal habitat for mycorrhizal species, which have been shown to help restrict root uptake of excessive nutrients, while assisting with uptake of less available ones.

A comment about home remedies from Catherine Daniels

In case you didn’t see yesterday’s comment that was added to Jeff Gillman’s January 6 post on home remedies, I’ve posted it here.  Dr. Catherine Daniels is WSU’s pesticide coordinator:

I’ve enjoyed reading the science-based information on your site. Keep up the good work. As regards home remedies, that is slippery slope, both legally and morally. Having a written definition of what you will or will not accept is helpful, especially if done in advance. Then you can be sure of being consistent and deliberate at least. There are both state and federal laws regarding pesticides, and state laws do vary. The most important thing is to know your state’s interpretation of those laws and to be mindful that with a blog you may be talking to people in state’s where laws are interpreted differently. I mention that for your legal protection. For example, in Washington State, if you talk to a user group (such as the public), and discuss the ways to use a material as a pesticide, it becomes a de facto pesticide recommendation. A legally-liable recommendation. When a researcher publishes information in a journal it’s not directed at a user audience so is not considered a recommendation by the author. If you take it to the public, at least here, it becomes a recommendation you made, unless you insert certain disclaimers. It’s always attractive to try and “help” the public find some easier, faster, cheaper solution to a pest problem. With pesticides and the public, you offer a better service directing them to a tested material which is registered and has a consistent concentration from batch to batch. Having personal safety and storage instructions is important…things that are missing in make-it-yourself squirt bottle solutions. Home remedies encourage people to think that the solution is “safe” (for people, not pests) because it’s made out of everyday ingredients. But as we know, the dose makes the poison. Nicotine is a nerve poison which you wouldn’t want a child to come into contact with accidentally because the squirt bottle wasn’t labelled or put in a safe place. I agree that our role is to educate, not police household cupboards or public pesticide use patterns. But by the same token, because we (educators)are trained to look at the big picture, there are good reasons to consider sticking to a label. Thanks for the opportunity to comment.

Pampas unpuzzled

Great discussion and answers on this one, gang!  Yes indeed, this is a plant out of place – as several of you noted.  But not only has it escaped from an ornamental landscape, it’s decided to grow, quite happily, in the median strip of I-5:

Another odd thing is that the species has not been officially recognized as invasive in Washington State.  It’s been languishing on the “Monitor” weed list for at least two years.  Our climate is a bit chilly for it, which may be part of the reason it looks so bad right now.  We had a very cold week back in November which may have killed this specimen back to the crown.  But never fear.  New growth will emerge this spring.  (Note to Washington State weed control board – maybe it’s time to list this plant as invasive???)

Finally, I do believe this specimen was sprayed last spring, as Jimbo pointed out.  However, it recovered and was able to send up two seed heads…which I’m sure have lavishly sprinkled the surrounding soil.

Will cabling a tree’s crown make it stronger?

In a previous column (December 1, 2010) I discussed the problems that wet, heavy snow can cause for trees and shrubs – particularly evergreens.  In response my colleague Terry Ettinger mentioned a cabling technique discussed in the 2nd edition of Arboriculture (1991).  I think it’s worth looking at the science behind this practice and some of the unintended consequences.

Harris’s Arboriculture text is considered the bible for landscape professionals, including certified arborists.  In the late 1990’s, Dick Harris was joined by Jim Clark and Nelda Matheny, two other gifted academics who have crossed over into practical writing.  In the 4th edition of this book (published in 2004), the authors caution about routine use of cables and other support systems for tree crowns.  They state that “evidence for the use of support systems to strengthen tree structure is anecdotal” and based on my reading of the scant scientific literature on the topic I must agree.

Older articles and texts tend to provide how-to instructions and diagrams on various cabling and bracing techniques, but little to no evidence supporting the practice. More recently, studies have provided evidence that drilling holes for cables, wires, bolts etc. increase the likelihood of introducing disease into otherwise sound wood.  As the tree continues to grow and change over time, even the best of these systems may need to be modified or replaced.  In fact, the systems should be inspected and maintained annually.  Crown cabling is not a permanent, one-time fix – and sometimes it isn’t even a fix.  Failures still occur, often just above the point of attachment of bolts and cables.  In fact, many arborists believe cabling should be the choice of last resort.

Some current research is exploring noninvasive methods of securing crowns, such as belt systems, that provide support without creating additional problems. As with any new technology, long terms studies are pending. Given the potential risks and lack of reliable benefit, I would not recommend cabling or bracing unless there were no other choices for saving the crown of a tree.

Friday puzzle uprooted!

Wow, we had some very creative answers on this one – and all of them made sense!  Peter, however, was spot on with his identification of roots (of a Thanksgiving cactus) growing in water (in an antique graduated cylinder).  I made it tricker by turning the photo upside down on Friday.  Here it is right side up:

What I love about this photo is that the various parts of actively growing roots are clear (more or less):  starting from the bottom you can begin to see the root tip and the hairless zone of elongation, followed by the zone of maturation with fuzzy root hairs, followed at the top by the area where lateral roots develop.</d

Last puzzle of 2010

I had a few weeks’ hiatus while scrambling around for the holidays – but have one last teaser for you before the close of 2010.  This photo is reminiscent of what Christmas trees will start looking like in the next few weeks. Can you figure out what it is? 

Ignore the parallel horizontal lines – they will be explained on Monday.  And yes, the photo quality’s not great, but the reason for that will be clear on Monday as well.

Have a very happy new year, and be sure to keep reading us in 2011!

Annual reporting – and you can help!

As many of you know, we Garden Professors justify our existence as faculty members every year through annual reporting.  Blogging is one of the newer educational opportunities that most university systems haven’t quite figured out how to measure and evaluate.

So we’re taking matters into our own hands. I’ve created a short survey to assess our effectiveness in outreach education in the blogosphere. 

The more feedback we get, the easier it is for us to make the case for continuing this effort.  (And feel free to suggest other questions or metrics we should include.  This is a first attempt on my part to create this feedback tool.)

Thank you all for a great year!