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

How to get rid of your lawn

With increasing interest in reducing monocultural swaths of turf, summer water consumption, and the drudgery of mowing, many people are eliminating part or all of their lawns.  We did this at home some years ago and can attest to the tangible benefit of reduced water bills during our dry summer months.

The question I often get is – how? Do you dig up the turf and throw it out, then fill in with topsoil? Or do you cut it, flip it, and then plant on top of it? Or do you cover it up with cardboard to kill it?

We’ve tried all of these methods over the years (except sheet mulch, because you already know what I think about that).  What I now recommend is the easiest, cheapest, and most effective way to both remove turf and protect the soil. Here it is in four easy steps:

1) Mow your lawn as close to the ground as possible. Scalp it. If you can wait until it’s not actively growing (summer here in the west), that’s even better. Don’t water it!

2) Cover it up with – yes, you guessed it – a really thick layer of arborist wood chips.  They need to be at least 8″ thick and can be as much as 12-18″ deep without negative effects. They will settle quickly, so you do need to put enough down to maintain a 6-8″ depth after a few weeks. The depth is important to suppress the turf as well as any persistant weeds (like those you can see in the above photo).

3) Wait. Turf decomposition will depend on temperature and water availability – warm and moist conditions are optimal. After 2-4 weeks, pull part of the mulch back and check out what’s underneath. When it’s easy enough to dig through, then you can…

4) Plant. Be sure to move the mulch aside and plant into the soil. Replace the mulch to cover the disturbed soil and keep the weeds down. It only needs to be 3-4″ deep at this point.

It’s that easy.

Flower demystification

As Paul suspected, this is a Phalaenoposis flower.  Here it is again, shown next to another flower on the same plant (but different stalk):

  

As to the second question – why does it look this way – there could be a number of reasons.  I’m leaning toward environmental.  This particular flower stalk is an old one – after it had bloomed initially (with normal flowers), we left it on after the flowers fell.  As often happens, new flower buds appeared, but all of them have been abnormal.  Some were completely fused and never opened.  This one is missing most of its petals.

Other reasons could include viral infection (as Sheila suggested) or somaclonal variation (common in tissue cultured plants, which is how many orchids are propagated).  But this flower stalk is perpetually colder than the rest of the plant as it’s closest to the window.  And since its first crop of flowers were normal, I think this variation is due to cold temperature interference during flower development.

If you have other ideas, be sure to post them!

Permaculture – my final thoughts

We’ve had some good, vigorous discussion about permaculture, specifically around the book Gaia’s Garden.  I’ve pointed out some problems with the author’s understanding of relevant plant and soil sciences and will wrap up this week with a look at the glossary and bibliography.

Glossary

The glossary contains a number of scientific-sounding words and phrases with unscientific definitions; for example:

“Buffer plants: Plants placed between guilds or between allelopathic species. They should be compatible with the trees in each guild and should have a positive effect on one or both of the guilds to be linked.” (“Buffer plants” is a phrase legitimately used in ecological restoration where plantings separate wetlands or other natural areas from human activity.)

“Guild: A harmoniously interwoven group of plants and animals, often centered around one major species, that benefits humans while creating habitat.” (The term “guild” is ecological and refers to groups of species that exploit the same types of resources.  It has been hijacked and redefined for permaculture.)

“Narcissistic: Plants that thrive on the leaf litter of members of their own family, such as the Solanaceae, or nightshade family.” (In this case, this is an unscientific term given a scientific-sounding – but nonsensical – definition.)

“Polycultures: Dynamic, self-organizing plant communities composed of several to many species.” (Polyculture is an agricultural term referring to the planting of multiple crops. It’s a cultural strategy in Integrated Pest Management.)

“Sectors: Areas where outside energies such as wind, sun, fire and so forth enter a site. These energies can be mitigated, captured, or otherwise influenced by placement of elements in the design.”

Bibliography

There are only two books I would consider scientific; one soils textbook from 1996 and the other is Odum’s classic text Fundamentals of Ecology (1971). I’m disappointed in how scarce and dated these references are, given the wealth of more recent articles and books that are both relevant to urban gardens and scientifically sound.

The bibliography also includes many books on design and I’m not including them in this critique. Of those that remain, the bulk are nonscientific and in many cases pseudoscientific. Examples of the latter include The Albrecht Papers (Albrecht, 1996), Weeds and What They Tell (Pfeiffer, 1981).

And this last criticism embodies what permeates much of Gaia’s Garden: pseudoscience. In the glossary, we see scientific-sounding terms or definitions that are ultimately meaningless or incorrect. Furthermore, we see scientifically legitimate terms such as guild used incorrectly. Both of these practices are characteristics of a pseudoscience.

I think this is unfortunate. I’ve mentioned before that I agree with much of the philosophy behind permaculture. But dressing up this philosophy as science both misleads nonexperts and alienates scientists.

So here’s a challenge – why not write a new book on permaculture and collaborate with a scientist? (I know a few who are writers!)

Friday puzzler unearthed!

Lots of good guesses this week! As many of you realized, this is a huge tree root making the best of a small tree pit.  But it’s not a Norway maple (sorry John) or a mulberry (sorry Robert), but a sweetgum (Liquidambar styraciflua) (congratulations Brian!).  (You can see the little mace-like seed pods on the ground.)  The root does resemble a bicep (“Treebeard’s elbow”) flexing to crack the concrete (aka Robert’s  Concretious blandmulsia):

Though sweetgum can be nice urban trees, their roots are quite vigorous and can lift sidewalks several inches above grade as they increase in diameter:

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Thanks for all the entries – our readers are smart and funny!

Yet another fine product

As a member of the GWA (Garden Writers Association), I routinely get emails about new garden products. Here’s one I received this week:

“I thought your readers or listeners might be interested in learning of a new way to protect their plants without using pesticides.  Moisturin, which contains no toxic ingredients, is sprayed on plants to form a clear flexible barrier strong enough to lock out both insects and airborne plant disease.  Moisturin is inexpensive, easy to use and extremely effective.  I would like to send you some at no charge for your own trial.  If your satisfied with it performance I hope you will pass it s benefits onto the people who trust your opinion.”

It turns out that Moisturin is simply a repackaged antitranspirant. Briefly, these spray-on barriers prevent water loss physically (by covering stomata) or physiologically (by closing stomata).  Interfering with stomatal function both reduces carbon dioxide uptake and water movement within the plant. You can read more about antitranspirants here.

But do antitranspirants have an effect on diseases or insects? Research indicates that while antitranspirants may reduce insect attack, their efficacy against diseases is less clear. They also show a clear negative impact on the plants they supposedly protect, to the extent they’ve even been tested as a form of weed control.

The best way to reduce pest and disease problems in garden and landscape plants is to keep them healthy. Reducing their ability to function normally by clogging their stomata will do exactly the opposite.

Short tree syndrome solved!

Good answers from Kenny S., Jimbo, Joe Schalk and Diana!  You were all skirting about the phenomenon of thigmomorphogenesis – or touch-induced change (also discussed in Jeff’s post of January 7.  The tests in the GP’s class are cumulative!).  In this case, the touch is wind.  Edge trees (or corn stalks) are more exposed and receive more wind, resulting in stunted heights and increased trunk diameter (you can’t see this last characteristic in the Friday photo).  Trees in the middle of the stand aren’t exposed to wind buffeting and put their resources into increased height. Similar stunting and thickening can be seen in urban plantings along the edges of sidewalks or anywhere people or animals routinely walk.

I spent my grade school years in a 1950’s housing development that had been Douglas fir (Pseudotsuga menziesii) forest.  The developers left many of the trees standing, and our backyard was full of tall, skinny and isolated Douglas firs.  When the Columbus Day storm (an extratropical cyclone, of all things) hit the Pacific NW in 1962, seven of these trees came down (none hit our house, fortunately).

Now of course a cyclone will take down many trees, regardless of their location…but this continued practice of leaving trees standing alone during development often results in blowdown or breakage of these now unprotected trees. 

Permaculture – more concerns

One of the gardening topics I’ve researched extensively is the use of landscape mulches.  (You can read a literature review I did a few years ago here.)  So I was more than a little frustrated to see one of the worst mulching techniques – sheet mulching – extolled in the book Gaia’s Garden (pp. 85-90).

Sheet mulches, like newspaper and cardboard, can be used successfully as a temporary weed control measure (i.e. a few weeks before planting a vegetable garden).  Long term, they are not a sustainable choice and often cause more damage to the system than the presence of weeds.

The two-dimensional structure of sheet mulches functions as a barrier to not only weeds but to the movement of air and water as well.  While this may initially increase soil water retention since evaporation is reduced, over the long term they will create soils that are unnaturally dry.  This condition is worsened on low-maintenance sites,where neglected sheet mulches easily dry out, causing rainfall or irrigation water to sheet away rather than percolate through.

In contrast, wet, poorly drained soils will become even more so as layers of moist paper or cardboard restrict evaporation and aeration.  Moreover, this condition encourages root growth on top of the sheet mulch, which can injure desirable plants when and if the sheet mulch is removed.

There are other disadvantages as well.  Exposed newspaper and cardboard mulches are easily dislodged by the wind, animals and pedestrians and often provide food for termites and shelter for rodents such as voles.  Combined with a somewhat marginal ability to control weeds compared to other organic mulches, sheet mulches are arguably one of the least attractive or effective choices for a sustainable landscape.

Sheet mulching proponents will argue that newspaper and cardboard are only part of the mulch structure – that organic materials such as compost and wood chips need to be added as well.  To which I respond – then why bother with the sheet mulch?  Why not just use deep layers of coarse organic materials?  That’s exactly what forest duff layers consist of.  It’s been repeatedly demonstrated that thick layers of coarse organic materials are the best and most natural choices for mulching.  (See, for instance, my  Ecological Restoration article on using a foot of arborist wood chips to suppress blackberry and enhance native plantings. )

The appeal of sheet mulching is its formulaic structure and logical approach – it’s like making lasagna (the name of yet another nonscientific approach to mulching).  Unfortunately, sheet mulching is neither natural nor particularly effective.