Author: Linda Chalker-Scott

My social media administrator (aka cat herder extraordinaire) reminded me recently that I’d written a post on xylem function and promised to follow up the next month with a post on how phloem works. Well, that was about 18 months ago. Guess I better keep my promise.

Do read the linked post if you don’t remember why “xylem sucks.” In contrast to xylem, functional phloem is an interconnected series of living cells with cell membranes. The presence of a membrane means the plant can regulate what goes in and out of the phloem, and the direction of phloem flow is determined by the relative concentrations of dissolved substances in the water – most importantly sugars derived from photosynthesis. Areas of high sugar concentration are sources; areas of low sugar concentration are called sinks. As these words suggest, phloem contents are moved from the source to the sink. This process is called translocation.

The most obvious sources in plants are leaves and other green tissues: this is where photosynthesis takes place and sugars are created. Other less obvious sources are woody roots, trunks, and branches: carbohydrate reserves are built up in the fall, as winter-hardy species enter dormancy and deciduous plants shed their leaves. Carbohydrates are re-mobilized in the spring when trees, shrubs, and perennials emerge from dormancy.

Like source tissues, sink tissues vary with the season but can also change daily – especially during the growing season. Expanding leaf and flower buds demand energy for building new cells; ripening fruits require large quantities of sugars. As new branches grow and produce leaves, their demand for carbohydrates decreases until they become source tissues. Translocation is a complex, dynamic process, where phloem in different parts of the plant translocate sugars in different directions.

This information can be used to guide your gardening practices:

Application of translocated herbicides. While we always want to reserve chemical weed control as a last resort, sometimes it’s necessary when other methods aren’t successful. Glyphosate (the active ingredient in Roundup) is applied to leaves and is carried through the phloem to sink tissues. When you read the label on a glyphosate-containing herbicide, it will mention that late summer/fall application is needed to kill the roots of perennial weeds. Consider hedge bindweed (Calystegia sepium), a pernicious and difficult weed to remove by mechanical or cultural means once it’s established in a garden or landscape. Glyphosate will successfully kill this weed but only if it’s applied after flowering. At that point the plant is no longer putting resources into either flower production or vegetative growth; instead, translocation moves carbohydrates (and the glyphosate) to the roots for storage over the winter. Killing the underground storage tissues means this herbaceous perennial will not reappear the next spring.

Pruning the crown during the growing season. When plants are actively producing new leaves and flowers, translocation is generally directed towards these tissues. Pruning leaf-bearing branches and stems has two consequences: removal of source tissues (the leaves) and increased demand for resources from the rest of the plant. Carbohydrates are moved from other sources, like remaining leaves and woody storage tissues, to the expanding stem and leaf buds that have been stimulated by pruning. This is why chronic and/or severe pruning can have a dwarfing effect on woody plants: woody storage tissues are depleted of their resources which are translocated to the developing buds. Until the new growth leafs out, it will remain a sink tissue.

Pruning the crown after transplanting. Take the information from the previous section and now consider the additional sink that has been created during transplanting. Successful establishment of a newly installed plant requires rapid development of new root tissues. Pruning the crown of new transplants siphons much of the stored resources away from the roots, reducing the rate of root growth and establishment. Reduced root establishment also means reduced uptake of water, which will damage the newly expanding buds and leaves. Bottom line: do NOT crown prune after transplanting, except to remove diseased, damaged, or dead branches. Wait until the following year to undertake any structural pruning.

It’s been 20 years since I began my Extension position at Washington State University. During that time, I’ve tackled gardening myths and produced peer-reviewed fact sheets and manuals through our Extension Publications department. But because of the way that Google searches work, these resources are often buried far beneath the glitzy but fact-free websites promoting bad science. This month I’ll be shining a spotlight on some publications that are must-reads for those who wish to use science-based information in their garden and landscape activities.

If the sheer vastness of the online swamp of information horrifies you, there’s no better place to start than with our Scientific Literacy manual. This publication, coauthored with Dr. Catherine Daniels, introduces you to the CRAP (Credibility, Relevance, Accuracy, Purpose) analysis of information from any source. As the abstract states, this publication helps you “to distinguish science from pseudoscience and can help avoid wasting time, money, and resources on poor ideas or, worse, scams.”

With the CRAP analysis techniques under your belt, you will appreciate our fact sheets debunking some of the “plausible nonsense” force-fed to gardeners (and by extension their plants and soils). The use of Epsom salt in the garden is one of the biggest fact-free nostrums out there. Our Epsom Salt fact sheet, coauthored by Rich Guggenheim, outlines what misapplication of Epsom salt will do to your garden soils and the news is not good.

Right up there with Epsom salt is gypsum, another popular soil amendment with many purported benefits. While gypsum can alleviate problems in heavily used agricultural soils, it has little to no benefit when applied to gardens and landscapes. Our Gypsum fact sheet, also coauthored by Rich Guggenheim, will tell all!

Since we’re discussing chemicals that are added to soils, I’ll refer you to another article written by Dr. Jim Downer and myself. Soil myth-busting for Extension educators – reviewing the literature on soil nutrition is a peer-reviewed publication in the Journal of NACAA. In this article we discuss address “six common misperceptions about managing soil nutrition in nonagricultural situations.” And yes, two of these misperceptions are the routine use of gypsum and Epsom salt.

I invite you to use the methods in our scientific literacy manual to debunk claims you read or hear about soil amendments. Knowledge is power and you can become a gardening superhero by helping fight the gardening swill that fills the informational swamp.

Next month I’ll continue the “truth series” with a look at some of our publications on garden practices we believe to be true…but aren’t based on science. In the meantime, here a couple of related blog posts that you might enjoy:

I do my version of the shame list with the “Dirty Dozen Garden Products.” Not only is this a good reviews of things that don’t belong on your garden soils, but there’s a fun quiz to see how your stack up with science.

This post on “Garden Logic” links up nicely with our discussion of CRAP analysis. Find out why we tend to jump to conclusions about what we see in the garden, regardless on whether it’s evidence-based or not.

Stay tuned for next month!

Wherever whitetail deer occur they present a challenge for gardeners. The internet offers abundant advice on this, but too often it is simplistic gardening myth such as scattering human hair or planting garlic.

Historically in deer control literature there have been occasional observations that deer hesitate to enter an area which looks too small or constrained for rapid escape. Finally, it came time to acknowledge and test this theory.

Green Island Preserve and the University of Minnesota Extension set about investigating this possibility through their Regional Sustainable Development Partnership (RSDP) program which provides support to community-benefit projects in partnership with private citizens and organizations. The test site was a 60 acre rewilded forest inside a small northern city. Deer pressure was heavy with resident herd numbers varying from 16-30 animals during the trial.

The first issue was defining a “small space” for testing the theory. In all the literature only one other trial of this concept could be found. It was conducted in Wisconsin with traditionally fenced spaces ranging from 15 ft by 15 ft to 21 ft by 21 ft feet during part of one summer. The Minnesota Green Island Preserve and RSDP trial chose 16 feet by 16 feet based upon the dimensions of manufactured, ridged cattle panels. These panels are 50 inches in height and 16 ft long and tend to be readily available at Fleet or Home stores even in suburban areas. If successful, their advantage would be very easy set-up and portability at a reasonable cost.

What was the result? Over 2 years of trial, this test demonstrated 95% success. Six micro-exclosures were established and planted within forested and forest edge locations in a zone of heavy deer pressure. During an observation period of 730 days, only one instance of deer browse occurred inside a micro-exclosure.

This success rate is more impressive because these fences are not a physical barrier to deer entry. They are strictly a psychological deterrent. This places them in much the same class as flashing lights, sound cannon, water spray, etc., but according to this study’s data, they’re actually more effective. All psychological deterrents have a failure rate dependent on application, monitoring, seasonality, rainfall, and more. But micro-exclosures show a low failure rate, without maintenance. If a deer breach does occur, the solution is simply to make the exclosure appear even smaller. This can be done by stretching rope across the center holding noticeable flagging. It can be lifted off when tending plants.

This is a highly promising discovery which merits further controlled testing by universities and professionals. The Minnesota Green Island Preserve and RSDP trial was specifically targeted to white tail deer predation while other ungulates present browse problems in other geographies. Rabbits were not addressed. However, until further and definitive research is conducted, citizen-scientist gardeners can contribute by testing versions of this method for themselves and adding their data to the general deer-control knowledge base. In using and testing micro-exclosures, gardeners will fare infinitely better than by spreading human hair, interplanting garlic, or buying “ultrasonic” gizmos.

This post was provided by Kent Scheer. Kent is a career sculptor with a side mission for reforestation and environmental compassion. He is the editor of three handbooks on sustainable agriculture resources and owner/ manager of a rewilded pine forest in northern Minnesota created for environmental education and awareness. You can contact Kent at kentscheer@outlook.com.

In the quarter century that I’ve been researching, publishing, and educating on the topic of landscape mulches, one thing has become clear: cardboard should never be used as a mulch. This viewpoint has been of great interest to gardeners; in fact, my earlier post has been the most frequently viewed post since it was published in 2015. I occasionally appended new information to the original post as needed, but the topic deserves an update.

Rather than rehashing what’s been written earlier (which can be found here, here, here, here, and here in addition to the link above), I’m providing information in a Q&A format that might be helpful:

Q: Is there research on using cardboard mulch in home landscapes?

A: Not much. To date, the only peer-reviewed research relevant to landscape soil conditions is our own work published in 2019. The abstract explains the importance of the results to landscape soil health as stated in the abstract (below):

“The orders of magnitude differences in diffusion coefficients among the mulch materials, however, could negatively impact a diverse soil environment such as those found in biologically rich landscapes with higher oxygen demands. Among the mulches tested, wood chips are a preferred method of mulching in terms of providing best gas permeability, particularly in landscape conditions.”

Q: Cardboard has been used as a mulch in agricultural production. Why doesn’t that research support using it in landscapes?

A: The goal in agricultural production is to maximize yield of an annual crop. In contrast, the goal in caring for a permanent landscape is to maintain a healthy soil ecosystem that will support plant life long term. The table below explains these differences in more detail.

Q: Okay, I understand that science doesn’t support using cardboard as a landscape mulch, but what about my vegetable garden? Isn’t the research on agricultural crops relevant there?

A: The research on agricultural production mulches is more relevant if maximizing yield is your most important goal. But your goals may include maintaining a healthy soil ecosystem, reducing the use of pesticides and fertilizers, and other criteria. Are you concerned about the established negative impacts that cardboard and other sheet mulches have on soil life? If so, then sheet mulches are not a good choice compared to chunky, three-dimensional mulches.

Q: I like reusing cardboard packaging as part of organic weed control. Isn’t that a good enough reason to use cardboard?

A: In addition to interfering with water and gas movement into the soil environment, corrugated cardboard has chemical contaminants that you really don’t want in your soil or even your compost pile. Corrugated cardboard contains environmental contaminants including dioxin and PFAs or “forever chemicals.” No gardener should want to introduce more of these widespread contaminants into their landscape or garden soils.

As I’ve been recommending for nearly a quarter century now, the very best mulch to use for treed landscapes is arborist wood chips. There is robust, peer-reviewed science establishing the benefits of arborist chip mulches in controlling weeds, enhancing growth and establishment of landscape plants, and maintaining a functional soil ecosystem. In contrast, sheet mulches such as plastic, weed fabric, and cardboard have demonstrated negative impacts on the long-term health of landscape soils. Any resource that says otherwise is not paying attention to the research-based facts.

I’ve been a gardening mythbuster for almost a quarter century. You’d think the quality of information would slowly be improving, given the increased sophistication of many gardeners regarding their information source. But every day my news feed connects me with articles that I’m sure some AI entity thinks will be enlightening. One recent story getting lots of eyeballs is entitled “The Benefits of Girdling a Tree Vs. Cutting It Down.” It makes for a good application of the CRAP analysis. While the link to the publication I’ve provided will go into more detail on CRAP analysis, all you need to know for this post is we’re going to assess Credibility, Relevance, Accuracy, and Purpose of the information.

First, let’s consider the Credibility of the source. According to HouseDigest.com, the author is “a plant mom…intrigued by nature and plant life which she exhibits by caring for and doting on her succulents.” Her college degree was in applied biochemistry, which has no substantial connection to applied plant and soil sciences. Bottom line, the author is not an expert in the science of tree care.

Let’s look at Accuracy next (we’ll get to relevance later). The author’s premise that girdling is “another great option” for tree management is grossly inaccurate. The article contains no links to any published research supporting her opinions, and demonstrates a lack of understanding woody plant physiology. The author states that girdling “would prevent erosion from occurring” in contrast to cutting the tree down which apparently removes “the tree roots acting as a protective cover for the soil.” Cutting a tree down removes its crown, but leaves the root system undisturbed. The roots stop transporting water aboveground (there’s no demand for it any longer) thought they can continue to grow as long as they have stored resources. Eventually they will die and their woody structure slowly decomposes.

Girdling the tree, on the other hand, does not prevent root uptake and transport of water through the xylem to the crown of the tree. It does prevent phloem movement of sugars and other resources from the crown to the roots. In other words, roots remain active in transporting water and nutrients but slowly starve to death without phloem-transported sugars and other resources. A good article on the topic of tree girdling goes into more physiological detail on the process that causes trees to decline “before entering an irreversible state of desiccation caused by definitive root death.”

Another possibility is that the girdled tree might send up new shoots below the girdling, leading to the formation of a new crown. Without constant vigilance in removing these new branches, the tree will survive and presumably continue to cause whatever problems that led to the original mismanagement.

The author also suggests that girdling is useful in preventing disease spread: “A sick tree would need to be killed in order to prevent the disease from spreading out to other trees and vegetation.” Or, if your trees “are hoarders by nature,” girdling renders them “incapable of taking in nutrients and being a burden to the environment.” Neither of these statements is accurate.

While the information in this article is somewhat Relevant to homeowners, it does wander into agricultural advice. We’re advised if we have “a danger tree or one that is resting on arable farmland with crops on it, it’s strongly advised that you chop it down and not girdle it. You don’t want an unpredictable girdled tree falling on your harvest, house, or worse — on someone — out of nowhere.”

At this point it’s worth noting that deliberately killing a tree by girdling also opens the property owner up to legal action should the tree fall and damage property or injure someone. This alone should be enough to dissuade property owners from taking advice from this article. And given the number of years it can take for a girdled tree to die (and eventually fall), is this really a useful process if you need to have a tree removed for some reason?

Finally, what is the Purpose of this article? It’s hard to know exactly why the author promotes girdling, and the language she uses in describing tree care is odd. Statements such as “sometimes circumstances call for trees to be put down and killed” and “trees need to be put down for all kinds of reasons” seem to equate trees with stray animals or dangerous wildlife. It creates an antagonistic situation where none exists.

Tree management, especially when it come to discussions about removal, needs to involve a certified arborist who can assess potential risks associated with leaving, as well as removing, any tree.

The emotionally-charged native plant debate only seems to be growing. Well-meaning but misinformed decision-makers continue to institute native plant policies with pressure from special interest groups. Most recently, North Carolina’s General Assembly weighed in on the side of emotional appeal rather than research-based information in mandating “that native trees, shrubs, and other vegetation are [to be] used for landscaping at state parks, historic sites, and roadways.”

Don’t get me wrong – I love native plants and recommend the use of well-suited native plants in gardens and landscapes. I’m co-author of a book that helps gardeners in the Pacific Northwest choose native species that are likely to thrive in their gardens. But the belief that native plants are superior to introduced species in urban and other unnatural areas is just a knee-jerk reaction to the very real environmental and ecological problems we face. It gives believers a false sense of accomplishment in that they can reverse significant threats such as climate change, wildlife extinction, and pollinator decline simply by using native plants rather than introduced species.

Supporters for this native-only policy list the same tired (and false) reasons that native plants are superior to introduced plants. Here are some of those reasons cited in the North Carolina decision, along with my commentary:

“There are many environmental benefits to native plants, and they are much more likely to thrive in our weather and soils” (North Carolina Department of Natural and Cultural Resources Secretary D. Reid Wilson)

• The concept of nativity is subjective and many scientists argue that such a subjective division makes it difficult to study, much less discuss, the benefits and drawbacks of introduced plants .
• This post by Dr. Bert Cregg bursts the bubble on some of the native plant superiority myths.
• Native soils are not the same as compacted, amended, and otherwise disrupted soils found outside natural ecosystems.
• There is no research to support that native plants thrive in soils that have been disrupted by development and urbanization.

“Native plants are adapted to the state’s environment and more likely to thrive, especially during drought.”

• Roadways, state parks, and historical sites are not natural environments (though some parts of parks and historical sites could be).
• Plants that can adapt to disturbed environments are most likely to thrive. Some of these are called weeds.
• Plants that can survive periods of drought have morphological and/or physiological adaptations for doing so. It has nothing to do with their nativity.

“They support pollinators essential to food production and ecosystem health and boost otherwise declining bird populations that depend on insects associated with native gardens.”

• One of the basic tenets of ecology is that new resources are exploited by existing members of a food web. What happens with one species of insect or bird or plant is not the big picture – ecology is the big picture.
• This blog post by Dr. Bert Cregg discusses a paper showing that exotic species can grow more quickly than native plants, but they are eaten more by herbivores.
• This  blog post looks at some of the research on insectivorous birds that contrasts with the claim that native birds require native insects.
• The most biodiverse landscapes are those with a high diversity of plants. The vertical structure of a landscape, created by the varying heights of trees, shrubs, and other plants, is crucial for bird habitat. I’ve published both a research article and fact sheet on this topic.

“Native plants, especially grasses, are better able to store carbon, thereby reducing greenhouse gases.”

• Native plants have supercharged photosynthesis? There’s a Nobel Prize waiting for someone to demonstrate that.
• Trees and other long-lived woody plants are best for storing carbon. Certainly not grasses. And the nativity of the woody plants is irrelevant to carbon storage.

“Native plants provide habitat for birds and other pollinators, are more resilient, and require less fertilizer and other maintenance.” (Brian Turner, policy director at Audubon North Carolina)

• Birds and plants have complex and often unexpected relationships. This post discusses a review article on the interaction between birds and those plants who depend on them to spread their seeds.

In June 2023, North Carolina’s Department of Cultural and Natural Resources installed a new 100% native plant garden in front of their DNCR headquarters. In comparing the before and after photos of the site, I’ve got a few observations.

• If storing carbon is important (as stated earlier), then cutting down all those trees and shrubs (which don’t appear to be invasive species) was an interesting decision.
• Why not just add a native garden to the existing landscape? That would have increased the plant diversity and retained the vertical structure, which is highly important for biodiversity.
• If we want stable, biodiverse landscapes in our urbanized environment, we must include the use of introduced species – especially trees. 

“This policy is a big win for birds and everyone who cares about North Carolina’s wildlife. It just makes sense. ” (Brian Turner, policy director at Audubon North Carolina).

• Nope. It’s a big win for dogmatic belief systems.

There are many things that we can do in our gardens and landscapes to maximize biodiversity. Spouting false claims about native plant superiority, garden shaming those who don’t eliminate introduced plants, and forcing communities, cities, and states into lock-step on what can and can’t be planted is not part of that process.

I’ve been doing horticulture myth-busting for almost 25 years now – and what I’ve learned is that myths are zombies. Not only do myths not stay dead, but new zombie myths are also continually created. One of the newest bright-n-shiny distractions is electroculture. It’s EVERYWHERE.

What is electroculture, you might ask? Well, Jaccard (1939) described it as “the stimulation of growth in plants by means of electricity passed into the atmosphere surrounding them or into the soil in which they are growing.”

There was a surge in research in the late 1800s through the early 1900s, partially due to earlier observations which tied electrical storms to improved plant growth. (Further research determined that lightning fixes atmospheric nitrogen into a solid form (nitrate), which dissolves in raindrops and enters the soil system. This was undoubtedly responsible for the reported improvement in plant growth after electrical storms.)

Scientific interest in electroculture tapered off with advances in plant physiology and the development of commercial fertilizers. Furthermore, the few scientific publications that came from early studies showed no consistent benefit from electroculture:

• “Favourable results in increased growth and yield have been obtained from time to time, but they are uncertain and largely dependent on weather conditions.”
• “Plants on poor soil are little influenced, since electricity…does not provide either nutrients or energy.”
• “A current of 10 milliamps inhibited growth in 5 plots, but in 10 others yields increased.”
• “Electroculture experiments produced no differences in the treated trees in growth or yield.”

In the 21^st century, a desire to use fewer chemical fertilizers has spurred renewed interest in electroculture. There are vast numbers of websites proclaiming improved plant growth from sticking copper wires in the ground. None of these are backed with any reliable evidence, but proponents argue that new research (since 2000) supports this practice.

I did a search of the scientific literature through AGRICOLA, CABI, and Web of Science/BIOSIS. There were zero publications after 1968. However, Google Scholar lists several. Google Scholar searches for publications in any form on the internet that have been authored by scientists. Here’s an example of what you will find:

• A 2021 conference report for the IEEE 13th International Conference on Humanoid, Nanotechnology, Information Technology, Communication and Control, Environment, and Management (HNICEM).”
• A 2021 Research Centre Lab report from the Late Ramesh Warpudkar ACS College Sonpeth, India.

These are not peer-reviewed, scientific journal publications. Even earlier ones from the 1980s are in irrelevant journals such as Journal of Biological Physics. Plant scientists publish in plant science-related journals. Researchers outside the field of plant sciences really have no clue how plants function, nor do they have the expertise to design experiments which consider the variables that affect research in applied plant sciences.

Yet, proponents of permaculture push this concept without evidence, using anecdotes as equivalents to scientific data. Conspiracy theories abound, with accusations that chemical companies have forced scientists to cease electroculture research.

Proponents of electroculture “rely on theories of geobiology and use light devices, antennas, or magnets intended to act on the cosmo-telluric electromagnetic fields of the universe, as in dowsing (Wikipedia).”

Worldwide, scientists consider electroculture to be a pseudoscience, particularly because it does not propose any plausible scientific mechanism to explain how electricity would stimulate plant growth.

If and when this changes – when recognized plant science experts publish positive results that are confirmed by other plant researchers – those results will be in bona fide plant science journals and be worth discussing. Right now, don’t waste your time with another horticulture myth that refuses to die.

If you are interested in honing your BS detector, please take advantage of this peer-reviewed Extension Bulletin.
My thanks to Sylvia Hacker for finding great vintage photos to help illustrate this post.

Last week there was much ballyhooing over a new article on the benefits of native plants in supporting insect populations. I’ve posted on the fallacy of native plant superiority before, pointing out that landscape biodiversity not plant provenance, is most important for supporting all types of beneficial wildlife. Despite robust, published evidence to the contrary, more people and governing bodies believe that native plants are the magic bullet for urban landscapes. (Never mind the fact that there are no plants native to urban environments.)

Using CRAP analysis to assess information:

• C = credibility. Are the authors experts in the field of interest?
• R = relevance. Is the information applicable to the field of interest (in this case, management of plants in urban landscapes)?
• A = accuracy. Is the information grounded in current, relevant science?
• P = purpose. What is the underlying reason that the information is being shared?

This most recent paper warrants a careful dissection as it has gone viral online. For me, the first red flag is that there are no plant or soil scientists on this team. The first two authors, who were responsible for developing the main ideas and designing methodologies, are both ecologists by training. The other authors are involved in insect collection and identification as well as ecological modeling. Not having plant and soil scientists on the team to ensure science-based practices are followed during landscape modification is a serious oversight.

The methods section regarding the study site is astonishingly vague, given this is essentially a landscape plant installation and management project (i.e., applied plant science, not ecology). A well-designed experimental project would include control plots, replication of treatments, site analyses (including soil type and texture as well as soil testing for nutrients and organic matter), and detailed explanations of how the site was prepared, how plants were selected, prepared, and installed, and what site management occurred post-installation.

Here is the section on how this “experiment” was designed:

“In mid- April 2016, 80% of the site was substantially transformed through weeding, the addition of new topsoil, soil decompaction and fertilisation, organic mulching and the addition of 12 indigenous plant species…Selected plant species met the criteria of being locally indigenous to the City of Melbourne and represented a range of growth forms— including graminoids, lilioids, forbs and trees— requiring no ongoing management such as watering and fertilisation.”

The purpose of the methods section is to provide detailed explanations on how the study was conducted so that it could be replicated by other scientists elsewhere in the world. There is no way to replicate this study properly, as the methods are vague and very possibly not based on applied plant and soil sciences:

1. “Addition of new topsoil” As we’ve pointed out in this blog numerous times over the past 14 years, you don’t add new topsoil to landscapes.
2. “Soil decompaction” What is this? Does it involve tllling, which would directly affect the health of the two existing trees?
3. “Fertilization” What is the fertilizer? When was it applied in the process? At what concentration and based on what data was it applied? You need to know baseline levels of nutrients before you can rationally add any fertilizer.
4. “Organic mulching” What material? Compost? Cardboard? Bark? How deeply was it applied?
5. “Addition of…plant species” Were these bare-rooted or simply popped out of the pot and dropped in the new topsoil?
6. “Requiring no ongoing management such as watering” News flash: newly installed plants REQUIRE irrigation during the establishment period regardless of their nativity. And this site now contains substantially more plants than before, meaning increased competition for water and other resources.

The problems with this nonscience-based approach to landscape plant management can be see by comparing the two spotted gum trees that were on site before this project began. Corymbia maculata is a threatened native species in Australia and the continued health of these trees should have been paramount before any site work was initiated.

Unfortunately, these sorts of projects, conducted by teams with no soil or plant scientists and published in journals that are not specific to urban plant and soil sciences, are neither well-designed nor useful. The mindset of many researchers outside the applied plant and soil sciences is that there’s no real science to preparing soil, installing plants, and maintaining the site. This current paper does not even meet the standard of being experimental: it is merely a report on what happens to insect populations when a landscape is altered. There is no basis for comparisons. Any conclusions drawn are anecdotal.

It’s bad science.

This past week I was out of town at a conference, and since the week was supposed to be a scorcher I made sure my husband was going to water the container plants daily. And indeed, temperatures were in the 90s, dropping to the mid-60s at night. But the container plants looked great when I got home and I didn’t think much more about it until the next day. My husband called me into the living room, pointing at our massive mophead hydrangea which looked like it had been torched. Leaves and blossoms were wilted and browning. Every single stem was affected. Since our landscape is on an automated sprinkler system, what the heck happened?

This is when caution and objectivity are important. I wasn’t going to go cut the whole thing down, even though it looked terrible. Instead, I made observations of the site (not just the plant):

• The site is on the north side of the house, where plant only receive direct sunlight in the morning and late afternoon during the summer.
• No other plants were affected – not even the smaller hydrangea to the west of the damaged plant.
• The irrigation system had been working normally.

When diagnosing plant problems, it’s also important to consider the history of the plant and the landscape:

• Hydrangea is at least 55 years old.
• No soil disruption or other site disturbance
• No pesticide or fertilizer use
• Mulched with arborist wood chips

Given that no other plants were affected, the problem was with the hydrangea itself. Hydrangeas use a lot of water to support their large, thin leaves and massive flower heads. When the weather suddenly turned hotter and temperatures stayed abnormally high in the evenings, the plant could not recover its water loss overnight. Many flowers and leaves experienced terminal wilt – that means they lost too much water and tissues turned brown. Other flowers and leaves were able to recover as day and night temperatures returned to normal.

What could we have done to prevent this? Had we seen the wilt occurring during the day, we could have turned on the sprinklers manually in that part of the landscape. Hydrangeas are a good indicator of low soil water. In future summers, as we continue to experience hotter and drier conditions, we will keep an eye on our hydrangea and use additional irrigation if necessary.

One of the most annoying weeds in garden and landscape beds is horsetail (Equisetum spp.), a genus native throughout North America and most of the rest of the world. They have survived since prehistoric times because they are highly adaptable to their environments and are almost impossible to eradicate. There is great debate among gardeners on whether to pull or cut horsetail. Online you can find statements such as this:  “…each time you break the stem, little portions under the soil regenerate new plants. Essentially, you will be creating more horsetail.” This and many other websites recommend cutting instead.

Unfortunately, this is bad advice. The trick to eradicating any perennial weed without chemicals (or at least bringing them to manageable levels) is to starve them to death. Plants depend on their roots (and rhizomes in the case of horsetail) to survive, so anything that reduces root resources is going to eventually kill the plant. Obviously the more above-ground material you can remove, the less photosynthesis occurs and fewer resources are transported to the roots. Pulling weeds, especially if done with a forked weeder (also used in this post), is going to remove far more material than simply cutting weeds off at the surface.

Once you start a weed removal project, you have to keep after it: once is not enough. There will be rhizomes or roots left underground to support new stem growth, and once they reach the soil surface they will start producing resources to send to the roots. “Constant vigilance” is needed to keep these shoots in check. You can significantly reduce the repeated pulling by adding a thick layer of arborist wood chips to the newly weeded site. This forces the roots to put even more resources into stem growth to reach sunlight, meaning fewer weeds and more successful, desirable plants.

There is one caveat for controlling any weed that spreads underground. If you can’t control the spread from adjacent properties, you will not be able to eradicate the problem. In such cases, you may want to install a root barrier along the edges of your gardens. You simply dig a trench and install the barrier of your choice, making sure there are no gaps between the sections. Treated timbers, concrete pavers, and other materials that are slow to degrade can be used. The depth is going to depend on your soil conditions and the weeds of interest; some preliminary digging to determine the depth where you find weedy rhizomes and roots will help. Keep in mind that root barriers will also interfere with the root spread of your desirable plants.

If root barriers are not an option, the other method you can try is to densely plant low shrubs and perennials along the property line to create a competitive line of defense. The roots will compete for space, water, nutrients, and oxygen; the crowns will create a shaded environment where invading stems struggle for space and sunlight. You will still have to watch for invaders, but the amount of weeding needed will be far less than it was before. And don’t forget the mulch, both for the benefit of your barrier plants and to force invaders to use more resources to get their stems to the surface.

This method works for ALL plants – not just horsetail. (Plant physiology is funny that way.) Bindweed, English ivy, Himalayan blackberry, and Canada thistle are all weeds that I have personally controlled through physical removal and deep mulching with arborist wood chips. If you’ve had success with this method on another aggressive weedy plant, be sure to post a comment!