September 2021 – The Garden Professors™

“Save the planet, (learn how to) plant a tree”

I like catchy memes as much as the next person. They’re easily memorized and passed on. But “Save the planet, plant a tree” has always bugged me for two reasons. First, and probably most importantly, this simplistic mantra absolves people of doing MORE to improve our environment. It’s a “one and done” approach: “Hey, I planted a tree today, so I’ve done my part.” That’s hardly a responsible way to live in a world where climate change is a reality, not a theory. Planting trees (and other woody plants) needs to become part of a personal ethic dedicated to improving our shared environment, and that includes reducing our carbon footprint in MANY ways.

Second, and more germane to this blog, is that most people don’t know how to plant trees (and that includes an awful lot of professionals who should know better). Planting trees properly requires an understanding of woody plant physiology and applied soil sciences. Otherwise, newly planted trees are likely to die due to one or more problems:

Poor plant species selection
- Mature size too large for site.
- Species not adapted to urbanized conditions. This includes insistence on using native species whether or not they tolerate environmental conditions far different from their natural habitat.

*Gaultheria shallon* does well in the forest subcanopy – not so well in urban settings

Poor/improper soil preparation
- Working amendments into the soil before, during, or after planting. Your goal is to keep a texturally uniform soil environment.
- Digging a hole before seeing what the roots look like. It’s like buying a pair of shoes without regard to their size.

The reality of tree roots: you can’t dig a hole until you can see what goes in it.

Poor quality roots
- Most roots found in containerized or B&B trees are flawed through poor production practices. If you are using bare root stock, you don’t have to worry about this problem.
- Can’t see the roots? Well, that leads to the next problem.

You can’t see root problems unless you take it all off.

Improper root preparation
- No removal of burlap, clay, soilless media, or whatever else will isolate the roots from its future soil environment. Take it all off.
- No correction of root flaws. Woody roots don’t miraculously grow the right direction when they are circling inward. They are woody; it’s like trying to straighten a bentwood chair.

Just try to straighten those circling, woody roots.

Improper planting
- Planting at the wrong time of year. It’s best to plant trees in the fall, when mild temperatures and adequate rainfall will support root establishment and not stress the crown.
- Not digging the hole to mirror the root system, especially digging too deep.
- Failing to place the root crown at grade (which means the top of the root crown should be visible at soil level). Look at forest trees if you are not familiar with what a root crown looks like.
- Stomping or pressing the soil around the roots. That just eliminates the air space in soil pores.
- Adding “stuff” like transplant fertilizers, biostimulants, etc. They are not needed and you risk creating nutrient imbalances when you add “stuff.”

The tape marks where the burlap ended – a good 10″ above the root crown.

Poor aftercare and long-term management
- Failing to add arborist wood chips as a mulch on top of the planting area. Regardless of where you live, natural woody material as a mulch is critical for root, soil, and mycorrhizal health.
- Failing to irrigate throughout the establishment period and seasonally as needed. Trees will continue to grow above and below ground, and without a similar increase in irrigation the trees will suffer chronic drought stress during hot and dry summers.
- Adding fertilizers of any sort without a soil test to guide additions. Trees recycle most of their nutrients; don’t add anything unless you have a documented reason for doing so.

There is nothing better for roots, soil, and beneficial microbes than fresh arborist chips.

That’s a lot to think about when you are planting a tree – but when you understand the science behind WHY these actions should be avoided, then you can devise a better plan for planting. And if it all seems to be too much, I have created a twelve-step planting plan that might be useful. Please feel free to share it widely!

Pruning Basics

As we head into Fall garden routines and leaves start to turn color, the smell and feel of the Fall weather is in the air. Winter is just around the corner and with those horticultural routines comes the urge to prune stuff . Both fruit producing and shade producing trees often get a hair cut during fall and winter months, herbaceous perennials are often cut back in the fall after bloom and before their winter rest so it seems a good time to blog about pruning before you get the urge! After years of pruning demonstrations for Master Gardeners and the public I have noted a common thread in how gardeners think about pruning. Pruning is a mysterious process. How we take that tangled mess of a plant (tree) and fix it? What do we prune? And the less frequently asked question: What do we not prune? To add confusion, some plants such as roses seem to have their own pruning “culture”. In this blog post I will cover the basic principles that apply to pruning all plants and then expand into specifics in upcoming blogs.

“Lion tailing” is a form of pruning that removes branches from the interior of a tree leaving tufts of foliage at the ends of branches. This kind of pruning is destructive to oak trees as it lets too much light permeate the crown of the tree

Plants don’t want to be pruned!
The first point is that no plant wants to be pruned. Gardeners prune plants because they think it is necessary for horticultural, aesthetic or safety purposes. Gardeners should temper their pruning by understanding plant responses that result from pruning. Generally plants don’t respond much when dead portions are pruned away. In some cases removing large dead portions of a plant will allow more light to enter and some response can occur, e.g., damage to portions of a plant not used to such sunlight intensity. So even a dead plant part may be doing something that you don’t understand. Also dead wood or dead plant parts may be part of some other organism’s home. Owls and other birds nest in cavities, some kinds of bumble bees will reproduce in old flower stalks of desert plants such as Nolina, etc. So dead plant parts are not always useless. If you are pretty sure that nobody else is using dead material go ahead and remove it if bothers your garden aesthetic.

This Ancient sycamore is falling apart with dead wood as younger stems continue to grow. The deadwood provides habitat for animals and in this location poses no risk to people so there is little reason to remove it.

There are two physiological responses to pruning

The two principles of pruning can be used to train plants and in the case of trees, produce a strong architecture that will not easily fail (drop branches). To achieve pruning goals two kinds of pruning cuts are used: the heading cut and the thinning cut. Heading cuts are often made in the middle of stems and do not have a branch that can take over the terminal role of the removed portion. Heading cuts are often used to reduce size or volume of plants. Thinning cuts remove branches at their origin. If thinning cuts are not too large and don’t allow excessive light into a canopy the plant will not respond by invigorating buds. Thinning cuts are used to maintain the natural form of a plant but can be overdone. Over-thinning results in plants that have so much light now entering that buds are invigorated and new shoot form in overwhelming and unnatural locations just as when heading cuts are made. Excessive use of thinning cuts can also produce trees that are “lion-tailed” where all the leaves occur at the end of Pom Pom branches. Remember from a tree or shrub point of view they don’t need or want to be pruned.

A **thinning cut** removes a branch at its attachment.

A **heading cut** removes a branch or stem without a side branch to assume its dominant role in the plant

Back to plant responses. There are two responses that most plants have to pruning. When living portions are pruned the remaining portions are then invigorated. This implies that dormant or “latent” buds will grow that would not ordinarily grow so plants will produce flowers or foliage in new places. In this way we can re-direct the growth of plants to achieve pruning goals we may have. This is how we can pleach a tree to grow flat along a wall or produce topiary shapes with shrubs. These kinds of pruning that dramatically alter form of a plant will require successive and significant pruning to maintain the altered form or shape. Not all plants can tolerate this and even those that do can be subject to sunburn or other processes that cause them injury. The second common response to pruning is that the more a plant is pruned, the less it will grow—pruning is a growth reducing practice. Even though buds are invigorated through pruning they can’t make up for the lost leaves and buds taken away without utilizing stored energy. The overall effect of having leaves removed is to slow the growth of the entire plant. Pruning when used as high art results in Bonsai plants that are really stunted individuals with highly stylized forms.

These plane trees along lake Como in Italy have been **pollarded** to dwarf them. Removing branches each year stunts the tree and limits its growth in a sustainable way. Pollarding is a style of pruning that requires continued removal of branches each year.

Pruning devigorates plants

Since pruning removes leaves and buds (which make more leaves) it is a devigorating process. You are taking away a plant’s ability to harvest light energy and convert carbon dioxide and water to sugar. All this happens in leaves. The fewer leaves a plant has the less sugar it can accumulate and then the less work it can do in terms of growing. On old or slow growing plants pruning removes energy needed for growth and also the energy needed to make secondary metabolites or chemicals which fight insect and pathogen attacks. This is why old trees pruned hard often died not soon after or become susceptible to pathogens they may have been able to fight before the pruning happened. Whenever you prune something think about how you are taking away photosynthate and what it might mean to the plant.

Fruit Trees and Roses

We have to prune fruit trees to make them fruitful? NO. Fruit trees produce lots of fruit when they are not pruned. The goal of pruning fruit trees is to modify trees so fruit is:
• in an easy to pick location,
• so there is less of it
• and so the fruit that forms is of higher quality.
An unpruned tree will make the most fruit but it may not be the quality or size you desire or where you want it in terms of picking height.

The same goes for roses. There are many pruning schemes for roses, but the most flowers will be found on the least pruned shrubs. Flower size is mostly determined by genetics. Shrubs that are severely pruned will have fewer flowers than their unpruned counterparts.

Roses have may pruning paradigms but the basic rules of pruning apply the more you prune it the less it will grow. The less you prune it the more flowers you will have.

Pruning and Disease

Pruning to remove diseased parts is often cited as a common garden practice. With some diseases like cankers and blights it is a good idea to prune out infected portions before they make spores or other inoculum to further infect the rest of the plant. In most cases it is important to prune well beyond the diseased portion so all of an infection is removed. Some diseases are “systemic” such as wilt diseases and while pruning will remove a dying portion it will not rid the plant of the infection. It is always best to identify the cause of disease even before pruning it from the plant. As we will learn in an upcoming blog I rarely recommend sterilizing your pruning equipment with disinfectants. A stiff brush and water is all that is needed when removing most diseased plant parts.

Pruning is a useful tool for gardeners. To get the most from the practice it should be conducted with knowledge of the effects it will have on the plant that is being pruned. This is quite variable and in some cases pruning is really contraindicated. While some plants like herbaceous perennials will be pruned to the ground either by the gardener or by frost, others maintain above ground architecture and pruning choices make permanent impact to many woody plants. In the next blog I will write about pruning young trees to create strong structure.

This Maten tree (*Maytenus boaria*) has a canker disease. A good reason to prune out branches, but in this case pruning may have been delayed too long as the tree will be quite disfigured after removing all the affected branches.

References:

Downer, J., Uchida, J.Y., Elliot, M., and D.R. Hodel. 2009. Lethal palm diseases common in the United States. HortTechnology: 19:710-716.

Downer, A.J., A.D. Howell, and J. Karlik. 2015. Effect of pruning on eight landscape rose cultivars grown outdoors Acta Horticulturae 1064:253-255

Chalker-Scott, L. and A. J. Downer. 2018. Garden myth busting for Extension Educators: Reviewing the Literature on Landscape Trees. J. of the NACAA 11(2). https://www.nacaa.com/journal/index.php?jid=885

Everything is chemicals: the myth and fear of “chemical-free” gardening

“Chemical-free” – a term I’ve seen several times attributed to many products, especially food and produce at farmers markets and even in gardening circles these days. This term is often misused to describe plants grown without the use of any pesticide, either conventional or organic. I have my thoughts that I’ll share later on that subject but first let’s talk about this “chemical-free” that gardeners, farmers, and others use and why its not only a myth, but a dangerous one at that.

Ain’t such a thing as “chemical-free” anything

At face value, the term “chemical-free” would literally mean that whatever the label is applied to contains no chemicals. That the entire item, whether it be animal, vegetable, or mineral is devoid of any and all chemicals. Factually this can never, ever be true. Everything that exists is made of chemicals. Oxygen, water, carbon dioxide, and any simple molecule, by definition, is a chemical. Plants and animals are organized structures filled with complex chemicals. Even you and I, as humans, are walking, talking bags of chemicals. The air we breathe, the food we eat, and the water we drink are all composed of a great mixture of chemicals. The use of the term “chemical-free” to describe anything is uninformed at best, and intellectually dishonest at worst. But a bigger problem, as we’ll discuss later, is that using the term can cause confusion and even fear of things as simple as food and as complex as science and medicine.

Expert reveals how even natural foods contain chemicals | Daily Mail Online — The “ingredient list” of a peach.
Source

What most people intend to say when they use the term “chemical-free” in relation to plants or produce is that they are produced without use of pesticides or conventional “chemical” fertilizers. Therefore, a better term to use would be “pesticide-free” instead of “chemical-free” as it more accurately represents the situation. Many may ask why the term “organic” or “organically grown” couldn’t also be used to describe “pesticide-free” plants. And while those terms would be accurate, organic production can involve the use of organic pesticides that are derived from natural sources such as plants, bacteria, or natural minerals. Natural sources of fertility for plants, such as composts and even soil itself, are all composed of a myriad of chemical substances. Plants don’t differentiate between the chemicals they uptake from compost or soil and those from fertilizers. To plants, nitrogen is nitrogen and phosphorous is phosphorous no matter where it comes from.

For some clarification on what different growing and production terms like these mean, check out this lecture I gave for the Oregon Farmers Market Association earlier this year.

While many have a strong opinion on the use of pesticides and fertilizers, I’ll state here that the use of any pesticide, organic or conventional, must follow the label on the container by law. And the use of any pesticide according to the label instructions means that the use of that pesticide should present a minimal risk to the health of the applicator, consumer, off-target species, and the environment. And don’t use any home remedy recipes or products that aren’t labeled (or at least scientifically researched) for use as a pesticide. In most cases these remedies aren’t effective, in some cases they can be more dangerous to human health or the environment than the pesticide they are trying to replace. And applying them as a pesticide could also be illegal.

Reading Pesticide Labels - Pests in the Urban Landscape - ANR Blogs — Pesticide label signal words that denote relative toxicity of a given pesticide.

Any gardener or producer, whether they use pesticides or not, should also be practicing Integrated Pest Management (IPM) to decrease or mitigate the effects of insect and disease pests on their plants. For those using pesticides, use of the least toxic pesticide that offers control of the problem should be the last step in a series of steps to avoid damage from pests after a threshold of damage has been reached. For those who don’t use pesticides, IPM should be a central practice in their gardening or farming practice. Unfortunately, the tradeoff for not using pesticides is often time and labor, so successful “pesticide-free” growing often involves more work (and for produce at the market or grocery store, a higher price). I have seen some gardeners and farmers who don’t use pesticides and don’t make an effort to practice IPM, taking whatever plants or produce mother nature and her children deal them. I’ve sometimes referred to this type of growing as “organic by neglect” as I see insect and disease riddled produce harvested and even sold at local farmers markets.

Why does it matter?

“So what if I use the term ‘chemical-free’? It doesn’t hurt anyone,” you may say. While this may seem the case, the use of the term “chemical-free” has risen as a result of what many call chemophobia, effects that reach far beyond the garden or the farmers market. This kind of thinking leads to the incorrect notion that all “natural” remedies are safe and all “synthetic” remedies are dangerous. True, many chemicals do pose a risk to human, plant, animal, and environmental health but many do not. Just like not all natural substances are safe. Poison ivy, anthrax, botulinum, and cyanide are all natural and cause everything from a skin rash to instant death (sometimes I get poison ivy so bad I wish for instant death).

This chemophobia can lead to, or is a symptom of, a broader mistrust of science, the scientific process, and modern medicine that has developed in society in the last few decades. Many attribute this to an anti-intellectual or anti-science stance in society resulting from mistrust or political saber-rattling against universities, education in general, science/scientists, “big Pharma”, “big Agriculture”, and others. As a result, the news is filled with people who eschew well-researched scientific advances that have been proven safe and instead turn to home remedies that have no such guarantee of either effectiveness or safety. The results can be worse than the effects of the proven advance the person was trying to avoid.

While the outcomes of “chemical free” gardening might not have such dire consequences as immediate death, the misuse of such terms can feed into a cycle of anti-science cause and effect, serving as both a cause and a symptom of mistrust of science and the scientific process. While everyone has a right to choose whether or not they use pesticides (or any other scientific advancement), making such decisions from a place of knowledge instead of fear is paramount for success and continued advancement.

Sources and further reading:

https://www.columbiasciencereview.com/blog/debunking-the-myth-of-100-chemical-free-slogans

https://www.sciencedirect.com/science/article/pii/S0278691520302787

https://www.canr.msu.edu/news/chemophobia-fearing-chemicals

https://www.businessinsider.com/what-chemicals-are-in-an-all-natural-banana-2017-6

Xeriscape – landscaping whose time has come.

With drought conditions or lower than average precipitation becoming more widespread across the country, it’s time to revisit the principles of xeriscape gardening. Let’s take a look at the “classic” principles and we’ll update them, Garden Professor style.
Note: If you’re growing food crops to supply your table not all of these principles will apply. Some will, e.g mulching, and some won’t. This blog post is focused on ornamental landscaping.

SO WHERE DID IT ALL BEGIN?

As an “official” landscaping technique xeriscaping seems to have begun in the early 80’s. Denver Water, the largest and oldest public water utility in Denver, Colorado, coined the term xeriscape in 1981 by combining “landscape” with the Greek prefix xero-, meaning ‘dry’. The utility then began to formally define the main principles of xeriscaping for members of the Denver community interested in modifying gardening practices to save water. The results were the Seven Principles of Xeriscaping, listed below.

THE SEVEN PRINCIPLES OF XERISCAPING
1. Sound landscape planning and design.
2. Limitation of turf/lawn to appropriate, functional areas.
3. Use of water efficient plants.
4. Efficient irrigation.
5. Soil amendments.
6. Use of mulches.
7. Appropriate landscape maintenance.

Let’s review them and apply some up-to-date gardening information.

1. “Sound landscape planning and design” – the ideal starting point for all gardens, “Right Plant, Right Place.” This principle earns a GP thumbs-up.

2. “Limitation of turf/lawn to appropriate, functional areas” – turf has a place in the landscape but perhaps not everywhere or in every landscape. “Right Plant, Right Place” (hmm, that sounds familiar). Another GP thumbs-up.

3. “Use of water efficient plants” – it may be stating the obvious but you want water efficient plants that work in your grow zone or micro-climate. Do some homework and choose plants that will be happy in your region. We’ll give this one a GP “OK” with a few points lost for being vague.

4. “Efficient irrigation” – this one has always been a puzzler. Perhaps it was included for folks who can’t break the habit of watering their gardens. The goal of xeriscaping is to have a landscape that does well on the average precipitation of an area. Granted in times of drought some plants may need a good drink now and then and new plants may need help getting established. But for the most part watering should be at a minimum and at the correct time, seasonally as well as weekly or monthly. Don’t forget to include any natural slope and drainage in your efficient irrigation plan. And “efficient” includes a correctly working automated system if you use one. This gets a GP “OK” as well.

5. “Soil amendments” – We now know that amending the soil is not a recommended practice. It interferes with drainage, causes soil subsidence and is not conducive to root growth. Plants need to be planted in native soil, whatever it may be. This one gets a big “F” for Fail and shall be removed from our list.

6. “Use of mulches” – if you’ve been following the Garden Professors blog you’ll know this is a winner. You also know that, ideally, we recommend using arborist chips but we also know that not everyone has access to them. Mulch choice also depends on the landscape site, plant choice and, in many instances, local codes. An organic mulch (but not bark) is usually the best bet, but there are times when an inorganic rock mulch is desirable. Do your homework and choose the best mulch for your situation. Mulch!
This xeriscape principal gets the GP Seal of Approval.

7. “Appropriate landscape maintenance” – too often xeriscapes are advertised as “maintenance free”; this is false. Like all landscapes and gardens xeriscapes are an artificial environment and require maintenance to thrive. Established xeriscapes will, hopefully, need less maintenance but they do need care. This can include dealing with weeds, regular inspection and maintenance of an irrigation system, and regular plant husbandry items such as pruning and clean up. This gets a GP thumbs-up.

So, based on the above discussion, here are The Garden Professor’s Principals of Xeriscape, Revised Version

THE SIX PRINCIPLES OF XERISCAPING
1. Sound landscape planning and design.
2. Limitation of turf/lawn to appropriate, functional areas.
3. Use of water efficient plants.
4. Efficient irrigation.
5. Use of mulches.
6. Appropriate landscape maintenance.

Looking over these principles we see no reason why they can’t be applied in every region and in every landscape. Learning to garden with what you have and where you are is the hallmark of a wise gardener.
Garden smarter, not harder.