What is an Urban Forest?

There are probably as many different definitions for an urban forest as there are people you ask. One definition on the internet stated simply it was a densely wooded area located in a city. Hmmmm, well. Do they mean a remnant of an original forest? Or are they talking about a planted park? Do these two features alone define an urban forest? What about those cities without remnant forests that claim to have an urban forest? I am picturing the cities that have grown out of the Great Plains which was prairie with barely a tree in sight.

Another definition I came across comes from Wikipedia: “An urban forest is a forest or a collection of trees that grow within a city, town or a suburb. In a wider sense it may include any kind of woody plant vegetation growing in and around human settlements.” (I like this a bit more.)

River Park, Hamilton, Montana, located along the Bitterroot River, providing natural habitat, walking paths, playgrounds and picnic areas in managed, yet still natural, setting.

Then a quote from the forest service website: “Over 130 million acres of America’s forests are located right in our cities and towns. Urban forests come in many different shapes and sizes. They include urban parks, street trees, landscaped boulevards, gardens, river and costal promenades, greenways, river corridors, wetlands, nature preserves, shelter belts of trees and working trees at former industrial sites.” Alright! Now, we’re talkin’!

I did find it interesting they specifically included “working trees at former industrial sites”. Actually, you could say all trees “work”. They are cleaning our air, replenishing oxygen into the atmosphere, taking in carbon dioxide, sequestering carbon, cooling our homes and streets, providing wildlife habitat, providing shade for those picnics and summer time festivals. They are mitigating storm runoff, reducing the heat island effect, and attenuating noise. They offer shelter and protection against wind. They provide recreational venues and the opportunity to find peace and tranquility in a hike.

Located on the campus of the Missouri State University in Springfield, Missouri, this beautifully landscaped bioswale is a great example of “working plants”; absorbing excess water and mitigating stormwater runoff, while containing erosion, photosynthesizing and looking beautiful while doing so.

If there are any of the above attributes you feel are undeserved, consider that not all trees perform the same functions in a like manner. Some trees have been misplaced (by us) which could minimize their abilities. Some are so mismanaged by us, they can offer only a mere shadow of their full potential. None of these circumstances are their fault but more often stem from our errors.

The Japanese Tea Garden, located in Golden Gate Park, San Francisco, California. While I have had the pleasure of visiting this beautiful garden, I don’t take credit for this photo. This was taken and generously shared by a friend, Nancy Togami.

An urban forest is not comprised merely of the street and park trees owned or controlled by a municipality. But, in my opinion, encompasses every plant in any built environment ranging from residential, semi-rural, exurban, suburban to the hardcore urban centers. And it doesn’t matter where they are planted. They might be located in a park, in boulevards, a private garden, downtown shopping malls, rooftop gardens, potted plants. They all count.

Notice I said “every plant”. If I were writing the definition, I would enlarge it to include every photosynthesizing organism. So we would include turf grass, annual and perennial flowers, herbaceous and woody shrubs as well as our long-lived, perennial trees. If managed properly, they all contribute to a healthier environment….because they ALL photosynthesize.

Photosynthesis is one of the two most important energy-related processes in the world, the other being cellular respiration. (See my blog Understanding Photosynthesis, which actually should be retitled to Understanding the Importance of Photosynthesis.)

If you live in a city that has an Urban Forest Management Plan, you may have seen or read the information on species inventory and the benefits these trees give back to the community. These inventories generally only tally the municipally-controlled trees and do not include those in the private sector which could easily double the number of trees and, therefore, the benefits provided.

Landscapes – A Work in Progress

A developing landscape

A landscape should be viewed as a work in progress. Its main components are living organisms which grow, spread and change as they mature at different rates and in different ways. What we start off with is not what we end up with, sometimes in ways we did not anticipate. And that is part of the fun and wonder.

Planting for diversity is a common theme in arboriculture and urban forestry. The premise is to preclude a major disease or insect infestation wiping out a majority of the urban (or natural) forest as has happened in the past and is ongoing in the present. Diseases such as Chestnut Blight, wiping out American chestnut trees, Dutch Elm Disease decimating American elms, Oak wilt killing trees in the oak species. Insect infestations are taking their toll as well. Emerald Ash Borer kills native and non-native ash trees and the Mountain and Western Pine Beetles have decimated pines across western North America. Most of this devastation is evident in the monoculture approach to planting and proves over and over the wisdom of having an urban forest comprised of a diversity of tree species.

When it comes to the individual landscape, diversity is equally as important, perhaps for more reasons than just surviving a cataclysmic event. It should include not just a diversity of trees, but a variety of plants from herbaceous and woody shrubs, annual and perennial flowers as well as grass species. Besides creating an aesthetically pleasing appearance, these all contribute to a healthy, living eco-system that becomes self-sustaining in a way many don’t appreciate.

Diversity in the landscape: trees, shrubs, annual and perennial flowers as well as grass species.

When considering diversity, you should consider not only species, but longevity, structure, size, characteristics such as blooming (or not), deciduous and evergreen. Why? Because not only does this give you a larger plant palette from which to choose, it also provides a more interesting design, will draw in an abundant variety of beneficial insects and will also contribute to diversity within the soil which means a healthier environment for the plants. This living eco-system you are developing does not stop at ground level but goes deeply beneath the surface.

Does your design matter? Only to the extent it meets your goals and desires. There are many designs and styles: Formal or informal; themes such as Italian, Oriental, English Country Garden, French. A design may meet your aesthetic goal but also serve a specific purpose: kitchen garden, xeriscape, encouraging pollinators and butterflies, or focusing on species from a specific area. It may be a combination of several. It doesn’t matter if it doesn’t fit into a specific designation or into many. What matters is that it suits you.

The wonderful thing, or I should say one of the many wonderful things about a landscape: it is never finished. It transforms itself daily if you pay attention, but even a casual observation will take note of the changing seasons with the perspective each gives. Then one day you realize you now have to look up to see the buds at the top of the little sapling you planted instead of bending down to note its growth. Perhaps that sapling is even now towering over your house.

The wonder of watching them grow.

Because you didn’t just plant trees, you planted understory shrubs and flowers, both perennial and annual as well, birds come in droves. Many of the annuals reseed themselves and so you have an ever-expanding flower garden that brings in pollinators and hummingbirds. Your landscape is now, literally, a-buzz.

Wildflowers amongst aspen and poplars. Forsythia and Bristlecone pine are banked by sunflowers.

Working in a garden becomes a time to share with a tremendous number of other living organisms as they go about their daily tasks. There is never a dull moment, many peaceful ones, but never dull. It is a time to let go of problems of the moment, let your mind wander. It gives you a task to focus on, gets you out-of-doors on your own terms, gives you physical exercise and mental stimulation. And at the end of the day, there is a self-satisfying feeling of accomplishment, the results of which you watch grow day-to-day.

Plant Health Care Workshops – A Report

Frankly, I had a blast! This is in reference to the Plant Health Care (PHC) workshops listed in my Upcoming Events page for this year, which by this time, I should have moved to past events. Well, we’ll see.

Four in all, they started in Dallas, Texas in March, then proceeded to St. Paul, Minnesota in April, East Windsor, New Jersey in May and ended up in Portland, Oregon in June.

Como Park Zoo and Conservatory, St. Paul, Minnesota. Japanese Gardens

The plus side to visiting Texas in March was the cool weather but the downside (if you are an arborist interested in seeing species of trees you normally don’t) was the trees weren’t in leaf. This was the case in Minnesota as well. I have every intention of going back to visit arboreta in these areas during am more conducive season with the sole intent to view trees to my heart’s content, or at least as long as my feet and stamina hold up.

Do I look cold??? Minnesota was pretty chilly. Thank goodness, my friend had a warm coat I could borrow. Minnesota Landscape Arboretum

The typical agenda for these workshops started off with Mike Raupp, Ph.D., an entomologist from the University of Maryland, introducing the order of go which included PHC basics, tree biology, key pests and key plants, progressing on to pest management, with my contributions on soil health management and tree diseases. Emphasis was made on improving cultural practices that might be influencing insect and disease pressure. Pesticide application guidelines were also discussed stressing the appropriate use of least toxic options first.

Arborjet sponsored Texas, Minnesota and Oregon, while Rainbow Treecare Scientific Advancements sponsored New Jersey. These companies gave a lecture on appropriate pesticides to use as well as an on-site, physical demonstration of their injection systems.

A highlight of these workshops, in my opinion, were the diagnostic walks with Dr. Raupp pointing out insect activity on various plants. There is nothing quite as helpful as being able to see the actual insect or damage from a specific insect in person with someone who can confirm exactly what you are looking at.

These workshops were a wonderful experience for me as well as the attendees: educational and fun in great locations.

Creating a Tree Island

One of the primary recommendations when planting a tree is to create a protective area around it, a buffer zone, separating the tree from the lawn. Which is where many people plant a new tree, smack dab in the middle of an existing lawn. Creating that buffer zone keeps out-of-control lawn mowers and weed eaters away from that vulnerable trunk. It is also good not to have the competition of grass, weeds or other dense growth right up to the trunk for other reasons as well including holding moisture against the trunk inviting fungal activity and providing cover for voles to creep in and munch.

This buffer zone is often called a tree island. In a previous blog, The Benefits of a Tree Island, I explain why you would want to create one. This zone not only separates trees and companion plants from turf grass but can also buffer them from other landscape features, such as hardscape.

A beautiful multi-species island at the entrance to the Cleveland Botanical Garden, Cleveland, Ohio

This area can be large but if that doesn’t suit you, it can be a small area. Creating this protective area is relatively easy and using the cardboard method described below precludes the need to use chemical herbicides.

Whereas we like to recommend mulching out to the drip line, if your area is too small to allow that, go with what you can as illustrated in this lovely, but small, back garden.

If this is a fresh planting and you have bare soil, great; you can skip Step One. Otherwise, read on:

Step one – If you have grass or existing weeds, scalp them as close to the ground as possible (without damaging the existing tree trunk). You can use a weed-eater if you stay well away from the tree. It is recommended you first create a buffer by hand-clipping or pulling any unwanted growth to a safe distance away from the trunk. Then scalp the rest of the desired area with whatever implement you have.

Step two – Thoroughly water the soil. Soil should be moist at least 2″ deep…not saturated, but moist.

Step three – Cover the area with a layer of cardboard starting at least a couple of inches away from the trunk. Slightly overlap the seams (if you leave gaps, you will have nice, tidy rows of weeds or grass). Thoroughly water the cardboard. If needed, you can secure the cardboard with landscape staples.

In this picture, we have just started to spread mulch. It will be brushed away from the trunk prior to finishing.

Step four – Top dress with your preferred organic mulch starting at least a couple of inches away from the trunk. Keep the mulch to a very thin layer at that starting point increasing it to a 2″ depth as you get further away from the trunk. You do not want to build up anything near the base of the tree. This is an area which should be allowed to dry out, not kept moist. And notice I said organic mulch. You want the benefits of decomposing matter to go into the soil.

This process will help control weeds for approximately 2 to 3 years in my experience. However, length of efficacy definitely varies depending on climate and the type and density of unwanted growth you are trying to suppress.

The cardboard will decompose in this time and you will have to replace it. However, in my opinion, this beats constant pulling of weeds and/or grass. And the decomposition process benefits the soil, worms and other soil organisms, turning this entire process into a multi-beneficial one.

There Are No “Trash” Trees

There are many wonderful tree species in the world. Far too many to rate or designate as to which ones are “the best”. Because “the best” becomes relative to area, site and personal preference: “Beauty is in the eyes of the beholder.”

Unfortunately, it is not uncommon to hear someone refer to a tree as a “trash” or “weed’ tree, implying it has no value. Sometimes this is in reference to a native tree that grows prolifically but doesn’t necessarily have a long lifespan, such as some alders, Alnus spp, or the water birch, Betula occidentalis, both common in riparian areas. But ecologically, they perform important functions. In addition, they can be beautiful additions to a naturalized landscape.

Sometimes the reference is to a non-native species commonly planted in the past which has proven to be less than ideal in the present. The silver maple, Acer saccharinum, and Siberian elm, Ulmus pumila, are examples. But a tree suitable for Zone 2, as is the Siberian elm, has a place in difficult-to-grow climates. And frankly, it is not the tree’s fault when planted in an area with a milder climate where they grow rapidly, seed prolifically and are often, in my humble opinion, managed poorly. This is often the case with both the silver maple and the Siberian elm. Planted suitably and managed properly both of these species can be assets to a property.

Acer saccharinum, silver maple, approximately 100 years old.

Many people do not live in areas where a luxurious climate offers an abundant diversity of species from which to select. When your options are limited, then each and every tree has a place and purpose and can and should include both native and non-native species if we are to achieve recommended diversity for long-lived sustainable urban forests.

Ulmus pumila,  A beautiful and well-maintained Siberian elm planted early 1900s.

Some species have acquired a “bad rep” due to fast but weak growth, potentially invasive qualities in their introduced home, production of substances which have proven problematical to people with allergies and now appear on banned lists in some areas. These are, for the most part, justified for specific areas but these condemnations should not be construed as limiting criteria everywhere.

Box elder,  Acer negundo

The box elder is a fast-growing tree in the maple family with a large native range here in North America. It is considered by many to be a “weed” tree. However, if you are in a challenging environment, this tough tree may be the perfect answer to a resilient shade tree.

Top Dressing vs Soil Amendments

The importance for understanding how you use a product is due to the potential ramifications of the application. A soil amendment typically refers to a product intended to be incorporated into the soil, and therefore, is generally well-decomposed. A top dressing generally refers to a product which will be laid on top of the soil and, therefore, may not be well-decomposed if at all.

Since those ramifications can be pretty extreme, you need to have a clear idea of your desired goal prior to making a final decision on the product you select.

Top dressing garden beds and/or around trees is an excellent idea for many reasons, not the least of which the benefits it gives to the soil. Bare soil is subject to degradation in many forms: wind and water erosion, compaction from rain and irrigation, soil microbes die off in barren soil, the soil can heat up enough to damage roots. For more details, refer to my blog Benefits of Tree Islands

Nature doesn’t like a vacuum; if there is an empty space, an organism is going to try to fill it up as soon as possible. Weeds love bare soil; they are the ultimate pioneer species. those are the species which come in and colonize abandoned, disturbed, or bare sites and can thrive in adverse conditions.

Weeds take advantage of bare soil.

Top dressing is a product you apply to the surface of the soil for a variety of reasons including (but not limited to): moisture retention, temperature moderation, erosion control from wind and/or rain, reduction of crusting due to rain and/or sprinklers, weed suppression, slow incorporation of organic matter facilitated by soil organisms, slow release of nutrients made plant available by soil organisms.

I am not a fan of using inorganic products such as pea gravel and rocks around trees and shrubs. The above list of benefits is best achieved when using organic products.

Organic products used as top dressing may have a high carbon-to-nitrogen ratio (C:N) as they are not well-decomposed. this generally means the ratio is 25:1 or higher. It takes longer to break down and provides a slow incorporation of organic matter to the soil as worms and other soil organisms process it. Common products include pine needles, bark chips, cardboard, or whole tree chips.

Whole tree chips refer to all components of a tree: leaves, twigs, wood and bark. We, personally, prefer whole tree chips because they have more of the components utilized by trees rather than just a single component.

Whole tree chips ready to be distributed around the garden.

If you are using top dressing to create a tree island, a flower bed or pathway, the goal might be weed suppression as well as other benefits and, in that case, using a product with a high C:N ratio which will take longer to break down is a good choice.

You certainly may use a partially or well-decomposed product as a top dressing but it may not achieve your desired goals if weed suppression is one of them. Well-decomposed product is already a growing medium (which is what makes it suitable to incorporate into the soil).

For more detail on why you don’t want to use a product with a high C:N ratio as an amendment which will be incorporated into the soil, please refer to my blog Will Adding Mulch Tie Up Nitrogen in the Soil?

Soil amendments are products you wish to incorporate INTO the soil. The reasons might be to increase the organic matter content sooner rather than later. Soil organic matter (SOM) is vastly important to the health of the soil, the soil organisms and the plants growing in the soil. It positively influences or modifies virtually all soil properties, including but certainly not limited to improvement in infiltration and percolation of water, increased nutrient exchange capacity, water-holding capacity and aeration. Amendments should have a C:N ratio of no more than 24:1. This may be a product you purchase or a compost made in your backyard.

Whether you are purchasing an amendment or have made the compost yourself, double check it is in fact well-decomposed prior to digging in. Criteria generally cited for “well-decomposed” are: it should smell “good”, be dark brown and crumbly.

The “good” smell is that wonderful earthy smell. It should not smell stale or like rotten eggs. This would indicate it is not thoroughly composted, is anaerobic or has other serious issues you don’t want.

The dark brown coloration is indicative of decomposed organic matter. The texture of the product should crumble readily; in fact, you should not be able to discern its origin.

If the product does not meet all of these criteria, I would hesitate to incorporate it into the soil. If it smells good but still has hard pieces in it, you can use it for top dressing, letting it decompose more fully on site.

© 2018 McNeill’s Tree Service

Plant Health Care

Plant Health Care (PHC) is a term often denoting a service offered by companies in the green industry indicating the company offers a comprehensive program to manage the health, structure and appearance of plants in the landscape. If they don’t offer an aspect of the program, they generally will be able to advise you on what is needed and offer referrals to a company that can supply that need or resources you can look into if the care can be managed by the homeowner.

A component of PHC is Integrated Pest Management (IPM) which is the diagnosis, monitoring and application of the least toxic choice in dealing with plant pests. 

Natural and applied methods are considered in IPM. Natural methods are environmental events which will stop the progression of the problem, such as a change in the weather that was conducive for a specific disease. An example being a disease pathogen may thrive in moist, cool conditions; the weather gets hot and dry, the disease progression ceases. If this can be anticipated, it will affect the choice of whether to apply any other method or let nature handle the situation.

Elm anthracnose 1
Anthracnose on elm; is it going to stay cool and wet? or dry out and get hot?

Applied methods are ones we have to implement. They include cultural, biological, mechanical controls with chemical control being used as a last resort.

We can’t eradicate all pathogens or pests from the environment. It isn’t practical nor is it desirable. IPM recognizes the need for a certain number of “prey” insects the “predatory” insects will feed on. Many diseases are endemic to an area and only become problematic given the suitable environment and the host species.

Whether the problem is insects or a disease, it is crucial to correct any cultural practice that may be contributing to the problem. Without doing so, it is pointless to apply any pesticides. Therefore, cultural controls are a first step in PHC/IPM programs.

Cultural controls
If available, plant resistant species for diseases known to be prevalent in your area. A classic example is dealing with fireblight, a bacterial disease potentially devastating to members of Rosaceae. Numerous cultivars of Malus spp, apples and crabapples, have been developed for resistance to fireblight as well as apple scab, powdery mildew and rust diseases. Combining best management practices and planting resistant trees may significantly reduce or even eliminate the need for chemical application.

Prairie Sky crabapple is bred to be resistant to the “Big 4” in Malus spp, fireblight, powdery mildew, apple scab and rust diseases

Landscape management practices may inadvertently contribute to establishing a suitable environment for diseases or creating a succulent smorgasbord for insects. An all-too-common example includes over-fertilization. Many articles, websites and well-meaning professionals advise the application of nitrogen as well as other plant nutrients in quantities exceeding plant need.

Excess nitrogen pushes vegetative growth at the expense of root development, storage and defense. This succulent vegetation is highly attractive to many destructive insects and nitrogen virtually feeds many pathogens causing diseases to be more virulent and prevalent.  Examples include Armillaria root rot, fireblight, fusarium, phytophthora, powdery mildew, pseudomonas and rust diseases.

Weed and feed products commonly sold for lawn care maintenance have herbicides in them that are designed to manage broad leaf weeds. Trees, shrubs and many flowers are broad leaf species and are susceptible to these herbicides as well. If weed control is desired in turf grass, it is far better to discretely spot treat if populations are beyond controlling by hand.

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Suspected herbicide damage from weed management in lawn under tree

Another cultural practice that influences the suitable environment is inappropriate watering. Too much and you will be suffocating roots creating a suitable environment for root rot diseases. Too little and you will weaken tree defenses making the plant more susceptible to opportunistic pathogens on weakened tissue as well as attracting some of the most damaging insects, the borers, who are drawn to drought-stressed trees.

Mowing and weed eating are often maintenance practices which cause physical damage to trees leaving wounds that become infection courts for both pathogens and insects. (See my blog Can A Weed Eater Really Kill A Tree?) Creating a protection zone (no-mow zone) around the trees, at least in a minimal mulched area if not a full tree island, will eliminate these man-caused injuries.  (See my blog Benefits of a Tree Island)

These are a few examples of cultural practices which should be evaluated and altered as needed.

Biological controls
Nature has provided many organisms which combat diseases and insects. In a balanced, natural setting these may be sufficient to keep damaging agents at an acceptable level. However, in our built environment, they may not be able to keep up with the task. It may be desirable to release biological organisms when they are not in sufficient numbers. Examples of these would be some of the bacteria, e.g.., Bacillus subtilis, that combat diseases such as fusarium and phytophthora or bacteria, e.g., Bacillus thuringiensis, that control numerous insect species.

Biological control may also include the release of predatory insects to control pests, such as lady beetles and green lacewings which are both voracious eaters of aphids. A side note: if purchasing these beneficial insects, lady beetles will be more effective in a closed environment such as a greenhouse unless there is sufficient food and water immediately available. Green lacewings may be a better choice in an open-air landscape.

061212 ladybeetle on vagabond aphid
Lady beetle enjoying a feast on a vagabond aphid

Mechanical or physical controls
Physical manipulation or creating an obstruction to protect plants can be very simple and effective. Examples would be fencing your tree to keep deer from browsing and rubbing or protecting the trunk of a tree to keep the neighborhood cat from using it as a scratching post.

This tree is not only protected against cat scratching but has a small mulched area providing protection from lawn care practices





Chemical controls
Chemical pesticides are kept as a last resort rather than a first so we have a place to take a final stand. With that said, there are some pests that have been identified as requiring the hammer approach first and last, just not nearly as often as some think. There is also a vast array of chemical pesticides to use including low toxic, organic, inorganic and synthetic products. Wading through the plethora of products is daunting and confusing. Trying to make sense of the labels can be just as daunting and confusing. It is strongly urged to consult a professional applicator prior to applying any pesticide yourself.

Broad spectrum cover sprays, sprayed over the entire property (plant population), will inevitably harm or reduce the number of naturally occurring beneficial and predatory organisms. These are the ones that can keep injurious pests under control and should be protected as much as possible.

Many pests are not damaging to long term plant health. Many pests are a nuisance to us more than they are a problem to the plants. And some need an aggressive approach. A good PHC technician should be able to help you wade through the potentials and come up with a game plan that will address the issues, causing as little negative impact to as many beneficial organisms in the environment as possible.

Biotic Diseases and What to do about them

Biotic refers to “living” as opposed to non-living which is referred to as abiotic.  Biotic diseases are pathogenic, infectious and can spread from plant-to-plant, generally of the same species.  They are caused by organisms such as fungi, bacteria, viruses, nematodes and mycoplasma-like organisms (MLOs).  (Please don’t ask me to explain MLOs.)   Fungal diseases are the most common but Iwant to stress that not all fungi cause diseases.  Most organisms are necessary and vital constituents in our environment. 

When clients call about a problem with their trees or other plants, they often do not know whether it is an insect or disease issue and many times do not consider abiotic issues at all.  However, many diseases actually stem from abiotic disorders as pathogens take advantage of a weakened or damaged plant. 

Diseases require three circumstances in order to develop:  1) A pathogen has to be present, 2) a susceptible host has to be available and 3) the suitable environment has to exist.  If any one of those criteria is not present, the disease will not develop. This is called the disease triangle. 

Many organisms exist in a non-pathogenic state performing necessary functions in the environment, only becoming pathogenic when a susceptible host and suitable environment coincide.  Trying to manage diseases by eradicating the pathogen is seldom (if ever) feasible or even desirable.  Instead, reduce the potential of a susceptible host or disrupt the suitable environment.

A plant with susceptibility to a disease becomes the host when the pathogen and suitable environment are present.  A number of plants have been specifically developed to resist common diseases.   Determine what are common and damaging diseases in your area and search out resistant cultivars of plants. 

An example would be many apple and crabapple trees are susceptible to four primary diseases:  fire blight, apple scab, powdery mildew and rust diseases.  There have been many cultivars of these popular plants developed with varying degrees of resistance to one or all of these common diseases.  Instead of fighting a likely problem, minimize the potential by selecting one of these resistant cultivars.


Prairie Sky crabapple is noted for resistance to fire blight, apple scab, powdery mildew and rust diseases.

A suitable environment is when the temperature and moisture are conducive for disease development.  And it varies from disease-to-disease.  We are somewhat at the mercy of Mother Nature here.  Cool, wet springs are going to be very suitable for certain diseases such as anthracnose. 

Anthracnose on elm

Many diseases are spread by wind and/or rain.  However, when you consider that water, not just in the form of rain, but irrigation practices as well, can create a suitable environment, then managing irrigation practices may go a long way to minimizing the potential for diseases being able to dock.

Knowing a disease’s life cycle may give a clue as to whether you should overhead water or not.  Some diseases are dispersed by rain or splashing water and, therefore, you would want to avoid overhead sprinklers.  However, some, for example powdery mildew, do not dock on wet surfaces. In that case, overhead watering susceptible plants, such as bee balm, Monarda spp, and crabapple trees, Malus spp, may be a good idea.  (Note: there are actually a tremendous number of plants susceptible to powdery mildew).   You need to know when the appropriate time of day to overhead water….and that may vary area to area.  Here in Western Montana, I have been successful at controlling powdery mildew by overhead watering in the early afternoon.  This timing may not work for you.   Note:  if a plant susceptible to powdery mildew is surrounded by plants susceptible to other fungal diseases that are enhanced by overhead watering, well, you have to pick your battles.

Some fungal pathogens thrive in a crowded environment which blocks air flow.  Judicious pruning that opens up the canopy may reduce the likelihood of the pathogen developing.

Pruning out diseased portions of a plant is often very effective at controlling certain diseases.  It is recommended to dispose of the debris off site.  It is also often recommended to prune fungal or bacterial diseased tissue from a plant during a dry period.  

Fire blight may be managed by pruning out the diseased portions and disposing off site.

Determining the most likely pathogens in your area, the environmental conditions under which they thrive and their life cycle combined with an inventory of your species listing their individual susceptibilities will go a long way in helping you devise a plan allowing you to minimize potential problems.  Nipping the problem in the bud….so to speak.

Abiotic disorders and what to do about them

Abiotic refers to “non-living” as opposed to biotic (living). An abiotic disorder is a plant malfunction caused by non-living, environmental or human-made agents. Yes, humans are living but generally the implements they wield which harm trees are not: e.g., lawn mowers, weed eaters, vehicles, herbicides. Another criterion that defines abiotic is they are not infectious. Animal damage is listed under abiotic as the damage they cause is not pathogenic or infectious. (I know, life gets confusing.)

When clients call about a problem with their trees or other plants, they often do not consider abiotic possibilities, rather assuming the problem stems from insects or disease.  The reality is the vast majority of time, the problem is abiotic in nature or stemmed from an abiotic injury.

Environmental extremes are beyond our control: e.g., lightning, heavy snow and wind. Damage caused by these agents should be assessed for prognosis of safety and survival and a management plan devised. Is the damage significant? Can it be rectified? Will the tree survive? Does it pose a safety issue due to proximity to infrastructure or human proximity?

Lightning damage

Wind damage

Heavy snow load bent limbs; subsequently straightened


Activities which cause abiotic injuries we can influence involve common practices in managing our landscapes.


Lawn mowers and weed eaters can be deadly weapons to trees. My blog, Can My Weed Eater Really Kill a Tree, goes in to this implement in detail. Lawn mower damage from constantly striking the tree trunk close to the ground is also a common agent of creating an infection court allowing diseases to gang a toehold but can result in progressive decline even without a disease. It is easy to discount incidental contact with a tree, thinking “it can’t be that bad”. But it can and it is.

Another lawn care practice potentially damaging to trees that many don’t consider is the application of herbicides in controlling broadleaf weeds.

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Herbicide damage on spruce tree

Many fertilizer products are listed as “weed and feed”, meaning they contain an herbicide in them as well as a fertilizer. This is supposed to address those pesky dandelions and other weeds in lawns. However, trees, shrubs and many perennials and annuals are broadleaf species as well. And in the case of trees and shrubs, their root systems may be occupying the same soil space as the lawn. What is applied to one affects the other. This is why we recommend creating tree islands or mulched areas around trees. (See my blog, The Benefits of a Tree Island)


Tying strings, garden hoses, installing swings or laundry lines by wrapping chains or line around limbs are another practice that may cause serious injury to a tree.

Dieback on limb

Dieback from previous photo caused by string girdling limb

This includes staking for stability after planting and the tags that come with the tree from the nursery. Limbs grow, but strings, lines, ropes and chains don’t. The tree grows around them often resulting in constricting the vascular system of the branch, stem or trunk.

And then we have irrigation practices. It is easy to get into a rhythm of watering without really checking to see if the plants are being appropriately watered. Consequently, it is all too common to see over- or under-watered plants. One size does not fit all. And, yes I am going to say it again, trees grow. As they get bigger, their water requirements increase. Not only that, but if you have a sprinkler system that was set up when they were first planted, the system needs to be moved away from the trunk.

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Drip system needs to be moved or possibly even removed. 

The roots are far away from the trunk and that is where the water needs to be applied. That growing trunk and buttress roots can also pinch off the water lines entirely.

Trees should be protected from animal damage before it happens. Waiting until you see the damage is too late. Some trees will stay vulnerable to animal damage their entire life and you need to make the decision whether you want to deal with that kind of commitment or pick a tougher species.

New scratching post for family cat

Planting herbaceous barriers to discourage browsing from larger animals may work but can backfire as they provide protection for rodents from natural predators.

Junipers planted around a crabapple



There are many products to discourage browsing by deer. I have had good luck with liquid products as well as hanging bits of Irish Spring soap from target trees. You may need to experiment to see what will be effective in your area. However, if you are in a particularly heavy use area, fencing might be your only reliable recourse. You can be as creative and decorative as you wish, or keep it simple but effective, combining form and function.  Works very well.

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Should I water my trees in the winter?

The answer to this frequently asked question, as with most questions pertaining to arboriculture, begins with the phrase “It depends…”  

The short answer would be “If they need it.”  Then a follow up question, of course, is “How do I know if they need it?”.

Some guidelines:

If you live in an area where the ground does not freeze and you have not had any precipitation, then your trees may very well need a drink or two in the winter.  

If you are in an area where the ground does not freeze and you are getting regular moisture, then you probably do not need to water your trees.

If you are in an area where the soil DOES freeze and you are not getting any precipitation...well, if the ground is frozen it will do no good to create an ice rink around your tree.

If you are in an area where the soil freezes and you have snow on the ground, you don’t need to water.

Freezing temperatures, snow on the ground…no need to water.

If you are in an area where the soil freezes but you have periodic thaws, if you have snow on the ground you do not need to water…the melting snow will take care of it. 

If you are in an area where the soil freezes and you have periodic thaws but no snow on the ground then check the melted soil….is it muddy?  You don’t need to water.  Is it dry?  You do need to water.

Above-freezing temperatures and lack of precipitation; opted to give this Bristlecone pine a drink.

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