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

Blog Survey Results, Part 1

I was gently reminded last week that I never published the results of our survey, asking our readers for feedback on the first full year of posting on The Garden Professors. All four of us are extremely grateful to those of you that participated, as we could use this information in our annual reporting and reviews.  Thank you all for taking the time.

To keep this from being too long for our blog, I’m going to just cover the first two questions today.  I’ll continue with this next week, where we’ll consider possible improvements to content and structure.

On the date we ran our analysis, 119 people had responded (the final number was 140).

Reason for reading

Science based information: 107 (90.0%)
Interesting and relevant topics: 101 (84.9%)
Ability to engage bloggers in Q&A: 39 (32.8%)
Usefulness as a CE resource: 75 (63.0%)
Entertaining approach: 78 (65.5%)

Some of the other reasons (you sent us lots!) included:

  • Friday quiz/mystery photos
  • Trusted source of information
  • Balanced and intelligent content
  • Diverse subjects
  • Ability to get feedback
  • Smart, funny, well-written, and challenging
  • Fun science fix

Behavior changes attributed to information on blog

Reduce use of chemicals, including fertilizers and pesticides: 52 (43.7%)
Reduced use of potentially invasive species: 40 (33.6%)
Improved ability to protect soil, including reducing erosion: 47 (39.5%)

Some of the other reasons included:

  • Stopped promulgating horticulture myths
  • Reduced use of peat moss
  • Improved ability to plant trees and shrubs
  • Improved ability to educate others
  • Improved ability to diagnose plant problems
  • More informed decision making about plant selection, gardening methods
  • Less work using better practices

[Sadly for some of you, I did not include the snide personal comments (about me) from trolls, irrationalists and/or the disgruntled. And to be honest, there were only 1 or 2 of these. But if you’re one of this little group, feel free to send your thoughts on to my supervisors! You’ll need to include your actual name and contact information, however, if you want your comments to be taken seriously.]

Should we use biochars in our gardens?

In the last few years, I’ve had a number of people ask me about biochar:  what  is it and what does it do?  Should they add it to their garden?  Should they make their own biochar?  So while the subject deserves a longer review, I thought it would be useful to discuss it briefly on the blog.

In the strictest sense, “biochar” refers to charcoal that’s made as a byproduct of biofuel production.  Various crop residues, livestock manures, and just about any other organic material you can imagine has been studied for this purpose.  Biofuel production not only helps diversify our energy resources, but the biochar itself also boasts several benefits, not the least of which is that it serves as a long-term, stable repository of carbon.  Since the carbon in biochar decomposes so much slower than the parent organic material, it is often considered to be a “carbon negative” material.

Even more exciting is that biochar offers some distinct, tested benefits to agriculture.  It is a porous, charged material that has been used to remediate soils by binding contaminants such as pesticides and heavy metals.  It offers a physical environment to mycorrhizae, which often benefit from biochar amendment.  It binds nutrients such as nitrogen, preventing runoff or leaching, and releases these nutrients to crops, most of which are shown to benefit from biochar additions.  The scientific literature is robust in examples, worldwide, of how various biochars benefit agricultural soils and crops.

But before you rush away to buy (or make) your own biochar, there are some significant caveats.  First, there is a sophisticated process used to make biochars, whose characteristics will vary tremendously depending on how they are produced.  Differences in temperature, for instance, will produce very different biochars from the same parent material.  (And you would be hard pressed to do this at home:  temperatures can range from 100-700C.)

Second, there is little, if any, research on the use of biochars in nonagricultural situations other than soil remediation.  This means no information on how it affects trees, shrubs, home gardens and landscapes, and other urban greenspaces.  As readers of this blog should know by now, there are many agricultural production practices that do not translate well to the home garden or landscape.

Third, biochars are generally very alkaline, often with a pH close to that of lime.  While this might be fine for some soils and plants, naturally acidic soils and their respective acid-loving plants are not going to react kindly to a more alkaline soil environment.

Finally, I hate to see people (and they are out there) who are now taking their pruning debris, arborist wood chips, and other organic material, burning it, and burying it.  Ideally, both bio-oils and biochar are made from excess crop residues and other debris generated in agriculture.  Arborist wood chips and other plant debris generated in a home landscape need to go right back onto the soil as part of a compost/mulch layer.  To burn this valuable resource strikes me as the classic “penny wise, pound foolish” mentality.

Friendly firs follow-up

Looks like I was too easy on you Friday!  Most of the you correctly noted that this “devil’s fork” is most likely the result of topping by a human or nature:

Devil's fork

Given that there are powerlines nearby, and more importantly a view to the water downhill, it’s likely that someone deliberately headed this Douglas fir (Pseudotsuga menziesii) back.  On the other hand, this species will commonly lose branches, and often their leaders, in a windstorm.

In any case, a tree that’s been topped and not correctively maintained is an invitation to disaster, and indeed this tree has sent up numerous new leaders.  With the proximity of houses, roads, powerlines, etc., it’s a classic hazard tree.  It’s too late to train the tree to a single leader, and the best long-term strategy would be to remove it completely and replace it with a species more appropriate for tiny urban landscapes.

Planting trouble: multiple trees in one hole

[I enjoyed Jeff’s Valentine story so much that I thought I’d stick to the theme of togetherness…for better or worse.]

A week or so ago a reader asked about the practice of planting three or four fruit trees in the same hole.  Having not heard of this before, I checked on the web and found many “how to” pages geared to home gardeners who either want a longer harvest of a particular fruit (early to late) or a mixture of different species.  Doesn’t it sound just great, especially for smaller urban yards?

One of these sites has these written instructions: “Plant each grouping of 3 or 4 trees in one hole at least 12 to 15 inches apart.”

Now, I’m sorry, but this is just asking for trouble down the road.  Readers of this blog know that root systems extend far past the drip line, and that roots from different trees are going to compete with one another.  You’ll end up with three unhappy trees, all jostling for space and resources, just like kids in the back seat during those long car rides.

But wait! you might say.  There’s research on high density tree planting, and it’s been shown to increase fruit yield on a per acre basis!

Yes, in fact there is a lot of planting density research on many different species of fruit trees.  What’s considered by researchers to be “high density” varies, but it rarely exceeds 2698 trees/acre (6666/ha for our international readers).  Optimal and sustainable levels of high density planting are also variable, as they depend on not only species but rootstock and the crown architecture; 1214/acre (3000/ha) might be a mid-range number.  This can be converted to a per-tree requirement of 36 sq. ft. or a 6’x6’ planting area.

How does this compare to the 12-15” recommendation given earlier?  If we’re generous and use the 15” recommendation, this translates to 6.25 sq. ft. per tree or 6970 trees/acre.  The 12” recommendation would lead to a whopping equivalent of 10,890 trees/acre.  (And no, it doesn’t matter if you’re using dwarfing rootstock or not; most of the higher densities in the literature are for dwarfing rootstocks.)

You don’t have to be a math whiz to see that these densities are totally out of line with reality.  Sure, you can probably keep overcrowded trees alive with lots of water and fertilizer, but they’ll be under enough chronic stress so that pests and disease might take hold, and fruit production will likely be poor.  And it’s about as far from a sustainable practice as you can get.

Landscape design – fatal flaw

So many great answers…so many problems with this landscape!  Everyone who made a comment was spot on in their reasoning.  And each of these flaws was completely preventable with good design.  But I’m not sure I would have been able to predict the problem that I now see every week at this location:

his area is the only access point for service vehicles of any persuasion. And sometimes they DO park on top of the planting strip.  Fred’s designation of these ground covers as “Stompus flatii” was perfect!

Lesson to be learned:  sometimes it’s best NOT to have planting strips if they clash with the realities of site use.

Friday quiz – landscape design

Down the street a ways from where we live is a relatively new condo complex wedged between a hill and the street.  A narrow planting strip separates the sidewalk from the street, as shown below:

The driveway at the top of the photo bisects the planting strip and dead ends in the parking area for the condos.  I have photoshopped this a bit, for reasons you’ll see on Monday.  But this is a true representation of the landscape.

I’d originally taken photos of this area for my ongoing “why trees die” collection (since all but one died within 2 years), but there’s something else wrong in this landscape related specifically to the design.  Can you figure out what it is?

Answers and more photos Monday!

Proposed phosphate fertilizer ban – a dissection of the criticisms

A few brave souls gave Friday’s homework assignment a good shot.  Ryan did a nice critique of the bullet points; Kenny did a little digging on WFFF, the organization behind the email; and Tom chimed in with the fact that Israel managed to do this a long time ago without impairing plant health.  Gold stars for all!

Here’s my initial analysis of the statements made, based on reading the bill (which you should do if you haven’t yet; it’s neither long nor difficult to understand):

WFFF: 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.

The bill: The legislature finds that: (a) Phosphorus loading of surface waters can stimulate the growth of weeds and algae and that this growth can have adverse environmental, health, and aesthetic effects; (b) Lawn fertilizer contributes to phosphorus loading. Limits on fertilizer containing phosphorus can significantly reduce the discharge of phosphorus into the state’s ground and surface waters; (c) Fertilizer containing no or very low amounts of phosphorus is readily available and maintaining established turf in a healthy and green condition is not dependent upon the addition of phosphorus fertilizer; and (d) While significant reductions of phosphorus from laundry detergent and dishwashing detergent have been achieved, similar progress in reducing phosphorus contributions from fertilizer has not been accomplished.

LCS:There is no identification of the “scientifically inaccurate statements” in the intent section, and as far as I can tell the statements are accurate.  The WFFF statement also misdirects the reader into believing that the intent section states that “turf fertilizer…is not necessary for a healthy lawn” when in fact the section (point c) states that healthy lawns can be maintained with low phosphorus fertilizers.

WFFF: 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.)

LCS:  It is unclear why this is a problem; both are state agencies.

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

LCS:  Where is the confusion?

WFFF:  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.

LCS:  This is misleading.  Not all organic products are “high in phosphorus”.  Furthermore, the phosphorus in organic matter is usually bound up in compounds that must be degraded before the phosphorus is available, making organic matter more of a slow release material.

WFFF:  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.

LCS: How is the “expertise of trained lawn care professionals” relevant to the bill, and how is this expertise not being recognized?  In fact, the bill creates increased expert oversight by working with Washington State University Extension specialists (faculty) in setting standards for applying phosphorus fertilizers based on soil test results.

WFFF:  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.

LCS: Unless there is a demonstrated need for phosphorus fertilizer (i.e. a deficiency verified by soil testing), there is no need to use it.  The routine use of phosphorus fertilizer without establishing a need is the behavior this bill seeks to limit.

WFFF: 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.

LCS: Again, unless there is a demonstrated need for phosphorus, it should not be routinely added to any garden or landscape.

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

LCS: This does not preclude people from purchasing it.

WFFF: 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.

LCS: This statement fails to inform us what the “primary causes of impaired water quality” are. How do we know that fertilizer runoff is not one of these causes?

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: