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

Foliage fun flaunted!

Not much activity on the Friday quiz! It was a tricky one. Take a look at our photos in total:

As you can see, these aren’t plant “problems” in the strictest sense. (The “landscape” in question is a retail nursery.) They are cultivated anomalies – little mutations that have been discovered and propagated. There are several points to this exercise:

1) Be sure you know your plant material! Many peope mistakenly assume that plants such as these are diseased, pest-ridden, or lacking some nutrient and need to be “fixed.” Personally, I don’t care for yellow cultivars; like Lisa B and Deb, I think they look chlorotic. Without identifying tags, though , it would be hard to know these are not deficient in nitrogen or some other macronutrient. I guess I would wait until leaves emerge in the spring: if they were yellow then and stayed yellow, I would presume the plant was a yellow cultivar.

2) Many of these cultivars are not particularly vigorous. A plant that’s missing much of its foliar chlorophyll does not photosynthesize efficiently and would probably not survive in nature. In our managed landscapes, however, we can nurture these oddities so they aren’t out-competed by other plants.

3) Cultivars such as these often revert to the wild form (remember Bert’s quiz last week?). The natural form (green vs. yellow leaves, or normal vs. dwarf stature, for example) is nearly always more vigrous than the mutation, and given the opportunity plants will outgrow these limitations. Thus, many cultivars require careful maintenance to remove “sports” before they overtake the plant.

Sunday rant – the evils of chemicals

It’s days like this that I am so grateful to have this blog at my disposal!

It’s 7 am on Sunday and I’m just finishing the paper, drinking Earl Grey tea, and listening to NPR. Liane Hansen just finished an interview with Martha Stewart, who among other things was discussing healthy eating for the new year. She’s a proponent of organic food (as are many of us), and mentioned two reasons she doesn’t like conventionally grown produce. The first – residual pesticides – is a legitimate concern. But then she stated her second concern that “chemical fertilizers in the soil are taken up and stored in the plant.”

No kidding.

Plants really don’t care (excuse my anthropomorphizing) where their mineral nutrients come from. Nitrogen in ammonium sulfate is the same element as the nitrogen in cottonseed meal. The plant uses it for amino acids, chlorophyll, alkaloids, and many, many other compounds.

Martha’s faulty thinking falls into the “organic is safer than chemical” mindset that way too many people hold (you can read a column I wrote about this in 2001 here). “Chemical” is not intrinsically bad and “organic” is not automatically safe. This is an emotion-based argument and inspires fear rather than thoughtful discussion. When someone parrots this mantra, I can’t take them seriously.

I believe that organic methods in production agriculture, ornamental landscapes, and home gardens are superior to conventional practices and support a healthy soil-microbe-plant-animal system. I also believe that many fertilizers are misused and/or overused – but this includes both conventional and organic varieties.

Gerald Holton, a science historian at Harvard, once stated that “persons living in this modern world who do not know the basic facts that determine their very existence, functioning, and surroundings, are living in a dream world. Such persons are, in a very real sense, not sane.”

This is the quotation that came to mind this morning.

Friday Foliage Fun!

Take a look at these three closeups of foliage from three different plants in a landscape in Washington state:

You’ve been asked to diagnose what’s going on in this landscape that would cause these foliar abnormalities. (I get photos emailed to me all the time asking these kinds of questions.) Bugs? Disease? Nutrient deficiencies? Environmental conditions? All of the above?

Invasives! Natives! No, wait, biodynamics

Just had to get your attention there. We’ve had a great discussion over native and nonnative plants over the last few weeks. I’m going to completely switch gears and move on to another topic – biodynamics.

If you’re not familiar with this term, let me refer you to my online column here. Biodynamics is a set of agricultural practices based on a belief system, not science, but is an increasingly popular approach, especially in the wine industry. (You can read a discussion of biodynamics in the vineyard in The Skeptical Inquirer here. This article is engaging as well as accurate – my column is pretty dry by comparison.)

Biodynamics is steeped in mysticism and includes special preparations that are used to treat soils and plants. Preparation 500, for example, is created by mixing water with manure that has been packed into a cow’s horn and buried for a set amount of time. Other preparations are more gruesome, requiring a stag’s bladder or cow’s intestine. A whole certification process has emerged in support of these practices.

While it may be easy to dismiss these practices, it turns out that biodynamic farms or vineyards are generally healthier than conventional systems. Does this prove a mystical force at work? Not at all. Biodynamic systems are also organic – using all of those good practices (low or no till, reduced pesticides, reduced fertilizers, polyculture, etc.) that have been demonstrated to be effective over decades of research. When comparisons are made between biodynamic and conventional systems, the impact of organic practices are hidden.

The few scientific studies that have compared biodynamic to organic systems – in other words, specifically testing the effectiveness of special preparations – have found no repeatable, significant differences.

Why do I even care about this? Well, it’s because it’s pseudoscience. It’s a practice that takes on the mantle of science, but doesn’t stand up to repeated scienific testing. Belief systems can’t be tested – even the inventor of biodynamics asserted that his methods were “true and correct unto themselves” and didn’t need to be tested.

Apparently simply being organic isn’t sexy enough anymore.

Is there any future for a scientifically-sound gardening magazine?

(You’ll see two posts from me today. This first one is easier to do at 6 a.m.)

One of the efforts I’ve been involved with is serving as science editor (and writer) for MasterGardener Magazine. We started this quarterly publication in 2007 (take a look at it online at it here) – not just for Master Gardeners, but for anyone interested in sustainable gardens and landscapes. Sadly, the publication went to an annual issue last year because of the economic downturn and now may be eliminated altogether.

Yes, this is a Washington state publication so when native plants discussed they are local natives. But the information itself is applicable no matter where you live. We had hoped at one time to offer regional issues, so that the magazine would have a local flavor.

Anyway, the publishers are no longer willing to carry a loss on the magazine. What they really need are advertisers.

Any suggestions out there? Most useful will be ideas that I can do from my computer or phone.

Veggie garden safety

A few months ago I posted a caution about using old pressure-treated timbers for vegetable gardens (see my Sept. 23 posting). I now routinely get questions about alternatives to these arsenic-laden materials, especially new treated lumber. What’s in the new wood that makes it rot resistant, and is it dangerous?

Rather than arsenic, new pressure-treated lumber has copper as its active ingredient. Though it also will leach out of the wood, there is not a human health hazard associated with its uptake by plants or animals. You probably get more copper leaching into the water carried through your plumbing (assuming you have copper, and not lead, pipes).

What about plastic timbers? Though I’ve not seen any literature about leachates from plastic lumber, I’ve seen some older plastic timbers that haven’t aged well – they can warp and twist. I would avoid those made of rubber, because decomposing rubber produces leachates that are quite hazardous (see September 30 for a discussion on rubber mulches).

Of course, there are many other materials one could use to corral their veggies – concrete blocks, stone, natural wood, etc. Do you have a favorite? Post a comment to let us know!

Friday puzzle solved!

Great discussion over the weekend, with some very astute observations. If you looked at the brown needles under the tree in Friday’s picture, you may have noticed that some of them weren’t needles:

Not only was this tree planted too deeply, as several of you pointed out, but the burlap and twine were left intact. It appears the nylon twine has already started to girdle the trunk, based on the trunk swelling just above where the twine is wrapped.

I’ve ranted about this practice already, so I’ll just sigh and move on to the first question – what directly caused the needle drop from the lower part of the tree? It’s a young tree facing west so the lower half gets plenty of sunlight. And though needle drop is normal with all conifers, the upper portion of the tree does not show the same drop with its interior needles. My guess is that ethylene gas is responsible.

Plant roots under stress often release ethylene, a natural plant growth regulator more commonly associated with fruit ripening. It also induces leaf drop, so as it percolates out of the soil it affects the lower leaves, but dissipates before it reaches leaves higher in the crown. It’s a common phenomenon with over-watered house plants.

Thanks to all of you who participated in the diagnosis discussion – this is more fun than my 20 years of college teaching!

Friday fun!

It’s the holidays, but this pine tree is feeling anything but merry. It was installed about a year ago. While the upper foliage looks lush and green, the lower branches have no new needles and in fact the current needles are dropping:

This is a two part question:

1) What might be directly responsible for the needle decline on the lower branches? (Hint: this is caused by the plant itself.)

2) What might be the underlying stress causing the needle decline? (Hint: this is caused by by people.)

Additional photos on Monday will reveal all!

Inspecting nursery plants, part IV

(Note: this is a really LONG post. Not in text – but in photos! Sorry for all the scrolling.)

I don’t know about you, but after spending three weeks on my hands and knees looking for trunk rots, surface roots, and suckers, I’m ready to become bipedal again. So today let’s look at trunks – and what shouldn’t be missing on them.

Many young trees have numerous short branches along their trunk, as shown in the photo below:

Unfortunately, many nurseries and gardeners think this looks scruffy, and respond by pruning these branches off, leaving a tree such as the one in this picture:

Personally, I think these trees look like lollipops, but aesthetics aside, this type of pruning can inadvertently damage young trees. Their bark is often thin and sensitive to environmental stress – especially sunburn. Without those short branches deflecting the sun from the bark surface, the living tissues under the bark can be killed, creating dead patches on the trunk:

How can you tell if the tree you’re considering has been improperly pruned? Just look for those tell-tale pruning cuts, as a close examination of the lollipop tree reveal:

In time, these trees develop thicker bark, and the lower branches are gradually shaded out as the crown increases. Be patient! Let your trees be a little fuzzy when they’re young. They’ll grow out of it.

Friday puzzle answers!

Good speculation on the rhododendron leaf damage! Jim in Wisconsin zoomed right in on the causes: the first photo was taken on a year where we had an unseasonable freeze right as leaves were expanding, and the second was taken on a year where we had unseasonably hot weather as leaves were expanding.

In both cases, the ultimate cause of damage is lack of water in rapidly expanding tissues. Once dormancy is broken, leaf and flower buds are highly sensitive to environmental extremes – they are expanding and are most sensitive to anything that interferes with water content.

During a freeze, leaf tissue water freezes, causing what’s called freeze-induced dehydration. It’s not the ice that causes the damage, but the lack of liquid water in the cells. Water freezes in the air spaces between cells, and osmosis draws water out of the cells into these intercellular spaces. Eventually the cells more or less implode once they’ve lost enough water.

During a hot episode, the roots can’t keep the rapidly expanding leaves fully turgid, and again necrotic areas appear as a result of water loss through transpiration and cellular “implosion.”

So both of these problems are caused by a lack of leaf tissue water – and it’s impossible to tell from looking at them whether it’s from cold or heat or salt or some other stress that reduces water availability.

Bottom line: keep track of seasonal abnormalities. It will help you to correctly diagnosis problems that show up some time later.