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

Cold Stratification for seeds

You may think of spring as the time for seed sowing, but I do a lot of seed planting now, in the fall. The reason is that most of the cold hardy perennials, trees and shrubs that I like to grow produce seeds that require cold stratification.
This simply means that they require a period exposed to cold temperatures while the seeds are moist and hydrated before they will germinate.

The requirement for cold is a pretty straight-forward adaptation to life in cold climates. Seeds that ripen in the summer and fall might not have time to get established before winter if they germinated right away. The requirement for cold means the seeds don’t actually sprout until spring, giving them a full growing season to get ready for the next winter.

seedbed — An outdoor seed bed is an easy way to stratify seeds

You can — and I used to — give seeds this cold period in the refrigerator. Three months in the fridge in a plastic bag with a damp paper towel to keep the seeds moist is long enough for most everything, though the exact period of cold required varies by the plant. The fridge works, but I think it is way easier to just do it outside. So the past few days I’ve been busy sowing seeds out in my outdoor seed beds. They’re just raised beds, filled with potting media, and covered with a screen lid to limit the number of weed seeds that blow in and keep disruptive animals out. I plant my seeds in the fall. Come spring, after the seeds have had their dose of cold, they sprout.

Dianthus seedlings ready for transplanting

Once the seedlings have grown on a while, I dig them out, separate the individual plants, and put them out into their final locations in the garden.

Individual seedlings separated and ready for planting

I do this with more and more seeds every year, even for perennials that don’t require a cold period to germinate, simply because it is so easy. No fussing around with lights or checking the calendar or even much watering. Just plunk the seeds in, and dig out the plants once they are big enough.

Watch a silly product morph into a lawsuit

A few years ago someone emailed me information on another garden miracle – this time a product called Mighty Wash. I found my notes on this product as I wondered what I should post about today. The sales information at the time advertised Mighty Wash as “frequency water” (which we’ll get to in a minute). Here’s part of the original advertisement:

Mostly water - plus "pink sauce" according to lawsuit documents — Mostly water – plus “pink sauce” according to lawsuit documents

“Mighty Wash is a new revolutionary way to solve your spider mite problem in all stages of development from eggs to adults…Mighty Wash is a ready to use “Frequency Imprinted” foliar spray. It is imprinted with special frequencies which target fleshy bodied insects. The use of frequency is nothing new to our world, and as you probably know all things have a frequency. What makes our products special is the fact that our proprietary frequencies are holding and stable for at least 2 years and running.

“One attribute of our Mighty wash is that it paralyzes the insect on contact not allowing it to flood out eggs and begin the resistance process! Essentially there is no resilience that can be gained from or product unlike so many others, and without the use of any chemicals. Mighty Wash does have very low levels of our naturally derived botanical oils, along with frequency make it the cleanest solution to your spider mite problem.”

Mites "flooding out eggs" [Photo source Wikipedia} — Mites “flooding out eggs” [Photo source Wikipedia]

When I looked for the manufacturer’s current information (an LLC called NPK), I couldn’t find reference to “frequency water” and its miraculous properties. After a bit of internet digging, I discovered that Mighty Wash was the subject of a bitter trademark dispute. For me, the best thing about this dispute is the deposition, which states exactly what the original makers of Mighty Wash claim their products do:

“Yeti invented and manufactures three plant washes using a confidential and proprietary formula and process that includes electronic frequency imprinting.”

They accused the defendant of making knock off products “not manufactured using Yeti’s proprietary formula and process” resulting in products “substantially less effective than Yeti’s Products.”

Leaving the legal battle for a minute, let’s see try to figure out how this product is manufactured. “Frequency Water” is water that’s been exposed to vibrational energy or to minute quantities of dissolved substances. That’s the “electronic frequency imprinting” which is referred to in the legal complaint; it’s also called “water memory” and is the foundation for explaining how homeopathic dilutions work.

Homeopathic medications are diluted until nothing is left except water [[Photo from Wikipedia] — Homeopathic medications are diluted until nothing is left except water and presumably the memory of the substance [Photo source Wikipedia]

It will come as no surprise to readers of this blog that there’s no reliable, published science behind any of this. What is surprising is the amount of money these companies make on selling water in a spray bottle. Mighty Wash and related washes (PM Wash, Power Wash, and Ultimate Wash [which is “Mighty Wash without food coloring”]) must generate healthy sales for two companies to squabble over the trademark of a product that is basically…water.

And the Irony Prize goes to the charges of fraud and false advertising leveled at NPK by Yeti Enterprises.

Microclimate follow-up

Last year I talked about using cheap min-max thermometers to get a handle on the specifics of the micro climates in my garden, and I was reminded recently that I never followed up on what I actually found out, so that’s what I’m doing today.

Remember that these results are just ONE data point, specific information about conditions in my particular garden. Your conditions will probably be different, so don’t try and extrapolate from these to your garden. Instead, if you are curious about your micro-climates, get a few thermometers, scatter them around, and see what happens.

What I did:

I placed thermometers three different locations – up in the air on the north side of a shed, on the ground out in the middle of an open area, and on the ground up against the south side of a shed. I expected the ground thermometers to be warmer, thanks to the insulation of snow, and the one on the south side of a shed to be warmer still, thanks to the added heat from the sun.

What I found

I was surprised on several fronts. First, the south side of the building was, for me, only warmer during the day. I recorded higher high temperatures, but at night, it dropped down exactly as cold as everywhere else. This may be partly because we have extremely cloudy winters here in Michigan, so there isn’t a whole lot of sun to warm up the south side of anything. The wall is also an unheated shed, so there was no extra heat leaking out from inside the way there would be up against the walls of a house, particularly if it is old and poorly insulated.

Ground level, under the snow, was as I expect warmer than the air temperature above. Much warmer than I had expected, in fact. We had about a foot or so of snow during the coldest part of the winter, and that snow kept thing more than 20 degrees F (~11 degrees C) warmer than the air temperature above the snow line. Keep in mind that the USDA hardiness zones are based on 10 degree F differences, so that thick layer of snow kept things almost two zones warmer. I knew snow was a good insulator, but I didn’t realize it would make that big a difference. Thank you Lake Michigan for all the frozen white stuff!

What I’m doing with the information:

I’m no longer trying to put tender plants against the south wall – Instead, I’m piling on a layer of mulch after the ground freezes to augment the insulating power of the snow. And given that south facing wall is much warmer during the day, I’m using it to grow heat loving plants that tend to pout in my cool, Michigan summers. Melons, peppers, and eggplant all adore the extra 5-10 degrees F (~2-5 degrees C) that south wall adds to my daily high temperatures.

Easy Overwintering

I love growing tender plants as annuals over the summer. But I don’t like buying them again every year, so I try to overwinter as many as I can indoors once frost threatens. However, I have pretty limited windowsill space, so I can’t keep many plants in active growth all winter. Luckily, I’ve found a simple hack that works for a surprising number of plants.

The above begonia is on a high dark shelf. It will sit there all winter, getting essentially no light, and I won’t water it. All those leaves will drop off, leaving nothing but dead looking stems. But come spring, when I put it back outside and water it again, new leaves will start growing and it will come right back.

Quite a lot of tender plants can do this. Just keep them dry, preferably on the cool side (unheated basements are perfect), and they’ll go dormant, usually dropping their leaves, and wait patiently for spring. I personally have done this with both cane begonias (as pictured) and the rhizomatous rex begonias, pelargoniums (the annual “geraniums”), and lots of succulent plants like agaves and cacti. I’ve seen first-hand other people using the same method with great success with brugmansia, bananas, and tender shrubby hibiscus. It seems like it is works most often with plants with thick, woody or succulent stems, but I keep trying it with new things and being surprised when they come through just fine. So if you’ve got some cool tender plant you’d love to over winter, but no window space left, shove it in the basement and see what happens. If it comes back fine in the spring, please comment on this post so the rest of us can learn from your experience!

— Joseph Tychonievich

Academic freedom vs. science-based advice

Those of you that have followed The Garden Professors for some time know that Jeff Gillman and I are relentless in our pursuit of gardening myths to explode. Social media – Facebook in particular – seems to be a natural breeding ground for dumb and/or dangerous home remedies that go viral. Most of these have no basis in actual science and are easy to dismiss. Other recommendations may have some science behind them, but a careful review of the literature often shows that the bulk of research does not support that particular practice or product. These ones are trickier to deal with, and nothing has been trickier for either me or Jeff than compost tea.

Nurseries often carry compost tea products (this one is now defunct)

The two of us have posted extensively on this topic in the last six years: just use the search function over in the left hand column of this blog and type in “compost tea”. You’ll find enough reading to keep you busy for a while. I summarized the state of the literature a few years ago in the now-defunct MasterGardener Magazine and to be honest the accumulated literature hasn’t changed much in terms of generating solid science supporting compost tea use. But its popularity seems to be increasing among landscape professionals and gardeners alike.

I get a lot of questions on compost tea from Master Gardeners in particular, who are bound by their positions as university volunteers to use science-based information. One of their major resources is the state university associated with their program – and recently this has become a problem for WSU Master Gardeners. Because on the Washington State University website you can find one professor who cites the lack of credible, consistent science on compost tea usage and another professor who provides workshops and webinars on making and using compost tea. Master Gardeners are understandably confused about what they can recommend and irritated that their university provides conflicting information. Why, they ask, does the university allow this to happen?

The answer is found in one of the most important values that universities protect: the academic freedom for faculty to speak their minds. Ideally this means that faculty can speak up about topics that are unpopular with university administrators without fear of reprisal, but it also means faculty have a soapbox on pretty much any topic they wish. And that’s whether or not they have any expertise or credibility on that topic. (For a particularly egregious example, one needs look no farther than prestigious MIT who has a research scientist with no expertise in biology or chemistry but who publishes articles in marginal journals linking glyphosate – the active ingredient in Roundup – to just about every known human malady.) Universities tend not step into this fray as it is a slippery slope – who decides what faculty speech should be censured and which should not?

How can Master Gardeners and others decide what information to believe? Well, that’s actually the mission of this blog and our Facebook page and group – to provide the best current gardening science and to help the public increase their scientific literacy skills. Science is not immutable – it advances as credible, published evidence accumulates. When and if compost tea ever becomes a consistent, effective product, we will be the first ones to share that information.

Add one species, get four new ones

Here’s an interesting twist on the whole native, non-native discussion… sometimes the introduction of new species of plants can trigger the evolution of new species of insects! Sometimes, in fact, a whole bunch of them, as is described in the coolest new research paper I’ve read in ages (Actual paper, behind a pay wall) (A brief Summary)

Introduce apples, trigger the evolution of four new species of insect

Basically, there is a fruit fly, Rhagoletis pomonella, native to Eastern North America that lays its eggs on the ripe fruits of native hawthorns. It is part of a whole group of species of flies that each go after a different kind of fruit – blueberries, snowberries and dogwoods each have their own species of closely related fly. When Europeans arrived and introduced non-native apple trees, the hawthorn fly started laying eggs on the apples as well, and got the name of apple maggot. But here’s the crazy bit: The hawthorn flies didn’t just expand their diet, they actually evolved to a new race, a new species in the making, that live exclusively on apples.

These flies have very brief life spans, so the adults must emerge at exactly the right time or there won’t be ripe fruit to lay their eggs on. But apples and hawthorns ripen nearly a month apart, so the apple targeting flies have evolved to emerge several weeks earlier than the original hawthorn flies. In addition to diverging in time of emergence, the two types of flies have changed their preferences in smells. The original fly is attracted to the smell of hawthorns, and avoids the smell of apples, while the new flies show the exact opposite behavior, each homing in on their target host, be it new or old.

The final piece of these two types of flies becoming two different species is that they each now mate only on the fruit of their tree of choice. This is important, because now the apple and hawthorn flies don’t interbreed due to their preference of mating location, and being a reproductively isolated group is the most commonly accepted definition of a species. Now the two types of flies will continue to diverge, as the lack of interbreeding means more and more genetic differences between the two populations will build up over time.
All of this is very cool, and has been long understood. Here’s the EVEN COOLER part from this new research: The divergence of one kind of fruit fly into two is cascading through the ecosystem. There are three species of parasitioid wasps that lay their eggs on the hawthorn fruit fly that have diverge into new forms that specialize in the new apple fruit fly. Just like the fruit flies, the timing of their life cycle, their preference and avoidance of the smell of the ripe fruit, and their mating habits have shifted to create different apple and hawthorn specific races. So where there was one fruit fly and three wasps, the introduction of the European apple has lead to the evolution of one additional fruit fly, and three new wasps.

I’m not sure what import this has, if any, in the ever raging native-versus-exotic debate in horticulture, but it sure is cool – the evolution of new species happening right before our eyes.

Joseph Tychonievich

Moss magic

In my opinion, no coastal Pacific NW garden is complete without moss softening the edges of a rock garden or nestling between paving stones. Now that the rains have returned, mosses are lush green sponges, absorbing sound as well as water. They are the finishing touches to our native landscapes.

A few months ago, however, mosses looked quite different. With our particularly hot and droughty summer, mosses were brown, dry and brittle just like our lawns. But unlike those dead blades of grass, the mosses were only in a state of environmental dormancy. All it took to revive them was water.

Here’s a patch of moss in our home landscape during a hot dry spell. It’s dry and brown:

Here’s the same patch of moss 20 minutes after I watered it:

It's a garden miracle! — It’s a garden miracle!

How can mosses recover so quickly? Well, mosses are one of the most primitive groups of land plants still in existence. They lack a true vascular system, so their “roots” are only anchoring structures – they don’t absorb water. Instead, water and nutrients are taken up over the leaf surface. As soon as water hits the leaves, it’s absorbed and literally throws the switch to turn everything back on. Leaves expand, chloroplasts start to absorb sunlight, and the photosynthetic machine is humming along.

In fact, my undergraduate major advisor was a bryologist (one who studies mosses). Jack Lyford’s lab was stacked ceiling-high with shoe boxes. Each box contained a different species of moss – completely dried out of course. All he had to do was take out a piece and place it in a dish of water. Within minutes it was fully functional and ready for study.

So make room for some moss in your garden. It’s a tough and fascinating little survivor.

Cactus grafting fun

I’ve been grafting cactus this summer, and made this:

It is a seedling of the gorgeous hardy cactus Echinocereus reichenbachii, grafted onto Pereskiopsis spathulata, an odd, leafy cactus I wrote about earlier.

Why do this? Other than the fact that it is darn cool? Well, because that vigorous, fast growing rootstock pumps a lot of energy into the cactus grafted on top, making the grafted cactus grow a LOT faster than left on its own roots.

grafted cactus start This is a (terrible, blurry) picture what the graft looked like when I first made it back in July. Just three months later it has grown to enormously, while the seedlings I left on their own roots look pretty much the same. I’ll let it grow on the graft for a while, then probably next year some time, cut it off, and move it into the garden, getting me to a reasonably sized plant in a reasonable amount of time.

So… if you want to speed up the growth of a pokey cactus, try grafting it. The process is crazy easy, lots of fun, and very thoroughly explained here.

“Lazy” corn and gravitropism

Inspired by Linda’s post about thigmomorphogenesis, I decided today I would add the word gravitropism to your vocabulary. It simply means growth in response to gravity. Shoots of plants grow up, because they are negatively gravitropic, they grow against the pull of gravity, while roots are positively gravitropic and grow down towards the pull of gravity.

And why is that so important? Well… this is what happens when gravitropism is missing.

To the left is normal old corn. The plant to the right was not sat on by a raccoon or anything, it simply has a mutation in a gene called lazy plant1. I’m not kidding. That’s the official, scientific name for this gene. Geneticists have fun with their names, though fruit fly geneticists are for sure the kings of silly gene names. This gene got that name because, as you can see, without a functioning copy of that gene, the corn plant no longer can detect the pull of gravity and so flops down in a “lazy” manner.

This corn is just odd, of course, with no real value (though it was fun to grow) but similar mutations are what give us some of the “weeping” or trailing forms of popular ornamental trees and shrubs.

Your new word for the day: thigmomorphogenesis

I just finished reviewing 4 manuscripts for three different journals and boy is my brain fried. My private reactions ranged from “I can’t wait until this one is published!” to “If I were to use sheet mulch this manuscript would be my first choice.” Anyway, it was the latter manuscript that got me to thinking about what can go wrong with experimental design, which brings up today’s word: thigmomorphogenesis.

This is a great word for those who enjoy figuring out word meanings by deciphering the (usually) Greek or Latin roots. (This exercise also helps you figure out how to pronounce it.) We have “thigmo-” which means touch, “-morpho-” which means appearance, and “-genesis” which means beginning. String them all together and you get the phenomenon seen when plants respond to mechanical stimulation by changing their growth pattern and hence the way they look.

Wind direction from the right creates an asymmetric hedge.

You can easily see examples of thigmomorphogenesis in everyday life. Look at a line of hedge plants where the plants on the end are more susceptible to wind movement and brushing by people, animals or vehicles. They are always shorter, aren’t they? Plants subjected to chronic thigmomorphogenic forces are generally shorter than their neighbors and thicker in girth. (For a longer discussion about how thigmorphogenesis works, you can read my online column.)

How does all of this relate to experimental design? Well, think about what happens if you are testing a product that requires applying it to the leaves of plants once a week. Your treatment plants are touched every week. How can you know that any changes in your experimental plants aren’t due to being touched? The way you eliminate this source of variability is by treating all of the plants the same way. When you are applying the product to the treatment leaves, you apply water (or whatever the solvent is for the product in question) to the control leaves. That way thigmomorphogenesis remains just an interesting tongue-twister and not a fatal design flaw in an experiment.