Bees and Avocado Trees: The Power of Pollinators 

Thanks to their delicious taste, creamy texture and the array of health benefits they provide, avocados have exploded in popularity over the last few decades. Formerly considered a delicacy for only the wealthiest among us, avocados are now a staple component in the diets of many. 

But unfortunately, avocado farmers are currently facing a number of challenges. One of the most significant is achieving sufficient fruit production from each tree. However, growers have potentially found a way to improve their yield. They just need help from a very special animal: the humble honeybee.

Read on to learn about the reasons that honeybees are providing a helping hand, and why your morning avocado toast may not be possible without the help of these six-legged saviors. 

Avocado Trees at a Glance

The avocado tree (Persea americana) is originally native to Central America, but it is now grown in dozens of locations around the world. However, Mexico continues to be the epicenter of avocado production, as the country’s farmers produce about one-third of the global annual harvest. 

Avocado trees grow best in warm climates, including tropical regions with ample yearly rainfall and places – like Southern California – with a Mediterranean climate, characterized by hot, dry summers and relatively mild, wet winters. Commercial avocado production obviously takes place outdoors, but individual consumers occasionally grow these plants indoors. 

Avocado trees may reach 60 feet or more in height, although most remain smaller than this. They are clad in attractive, deep green leaves, and they are available in a number of different cultivars. 

Avocado Flowers: Peculiar Pollination

Avocado trees produce an incredible number of very tiny flowers, measuring about 1 centimeter (roughly one-half inch) in diameter. Indeed, large individuals often bear one million flowers or more. However, only a very small subset of these flowers will set fruit – typically on the order of 100 to 200, although occasional trees may produce as many as 500. 

The reasons avocado trees only produce a relatively small number of fruits aren’t entirely understood. However, it likely has to do with the strange flowers these trees bear and their unusual pollination mechanism. 

Avocado flowers have male and female reproductive structures. However, they aren’t simultaneously functional – they function as males or females for a short time before closing up and reopening later, when they function as the opposite sex. After the second opening sequence has completed, they close permanently.

Different avocado cultivars exhibit different pollination patterns. Some – known as Group A – function as female flowers in the morning, before reopening and functioning like male flowers in the afternoon. Cultivars in Group B exhibit the opposite trend. They function as male flowers and release pollen in the morning, before becoming receptive to pollen later in the afternoon. 

This mechanism is often thought to have evolved as a way to prevent self-fertilization. Because the flowers on a given tree are typically functioning as one sex or the other at a given time, it is unlikely that a tree will fertilize itself. Instead, the pollen from one needs to reach the female flowers of another avocado tree.  This tends to make avocado tree pollination relatively inefficient. So, avocado farmers are increasingly seeking help from pollinating insects – specifically honeybees. 

Honeybees Lend a Helping Hand

While honeybees don’t seem to have a particular affinity for avocado flower nectar, they can and do visit the flowers routinely. In doing so, they often transfer pollen from the male flowers of one tree to the female flowers of another, thereby achieving pollination and – in some cases – fruit set. 

Honeybees aren’t the only insects that participate in avocado tree pollination, but they are among the most helpful. Additionally, given the fact that honeybees are widely available from apiculturists (beekeepers), they are easy to introduce to groves. 

Historically, avocado farmers would install one or two honeybee hives per acre of avocado trees. But in recent years, farmers – and the university researchers who study the interrelationship between avocados and bees – have begun using more hives per acre. Currently, many farmers are using twice as many hives per acre, and some growers are using even more bees to achieve good fruit set. 

Some farmers have also begun tweaking their planting and maintenance practices to help the honeybees accomplish their work more efficiently. For example, some have begun altering their pruning practices. This is done in the hopes of keeping the grove more open, which provides better flight paths for the bees to move between trees. 

Interestingly, honeybees appear to be more helpful in avocado tree farming in some places than others. For example, they’re often quite beneficial for growers in southern California, but they prove less helpful in places like New Zealand, where hand-pollination seems to be more effective.  

One possible solution for these farmers may come from some of the relatives of honeybees. Some have begun experimenting with bumblebees, who’ve reportedly increased avocado yield in some locations, while others – including growers in San Diego County – have turned to New World Carniolan bees. 


If you’re one of the many southern California residents trying to produce your own avocado crop, you are surely already familiar with the challenges these trees present. But we’re here to help! If you need assistance keeping your trees healthy or improving your crop yield, give your friends at Evergreen Arborist Consultants a call. One of our ISA-certified arborists will visit your property, inspect your trees and provide a recommended course of action.  

Four Ornamental Trees That Won’t Create Litter Problems

Thanks to the myriad resources available to modern homeowners and property managers, many people conduct a lot of research on the trees they intend to install. They look up things like the tree’s water requirements, sun-exposure preferences and susceptibility to common pathogens and illnesses.

This is obviously a good idea, and it’ll help you avoid planting trees that won’t thrive in your desired location. But, many people forget to consider one key characteristic when doing their homework. They forget to investigate the littler problems created by the tree.

Trees can create litter problems in several ways. Some shed pieces of bark throughout the year, while others blanket the ground in fruit during a relatively small window of time. Others may shed entire branches sporadically (which can also represent a safety hazard).

We’ll try to help you avoid doing this below, by discussing four good ornamental trees that won’t create a mess in your yard (and be sure to check out our article that identifies some of the trees that cause the worst litter problems, so you can avoid them).

1. Shoestring Acacia (Acacia stenophylla)

Many acacias are notorious for creating significant litter problems (we even mention the Chilean acacia tree in our article about the trees that produce the worst litter problems), but the shoestring acacia is a different matter entirely. Unlike many of their relatives, which carpet the ground with dry fruit and thorns, shoestring acacias rarely present these types of problems. Reaching 30 feet in height, these trees have a unique, “weeping” look and they produce attractive yellow flowers throughout the fall and winter (which provides additional value, as few other trees are very colorful during this part of the year).

2. Fruitless Olive (Olea europaea)

For obvious reasons, fruiting trees are rarely good choices for those seeking low-litter trees, but the fruitless olive is an exception – as its name suggests, it produces no fruit. But aside from the lack of fruit production, fruitless olive trees provide all of the same traits that make olive trees popular with many homeowners and property managers. Olive trees typically grow as multi-trunked shrubs, but they reach tree-like sizes; many specimens eventually reach 20 to 25 feet in height. Olive trees are ideally suited for Southern California’s Mediterranean climate, and they rarely require much supplemental irrigation once established.

3. Willow Acacia (Acacia salicina)

The willow acacia is another interesting-looking tree that produces very little litter. A medium-sized tree, most specimens will stand between 20 and 40 feet tall. Willow acacias often exhibit a weeping growth habit, and they have an attractive gray bark, which is often visible beneath the canopy. Willow acacias are hardy trees, who tolerate a wide range of soil types, and they will grow in full sun or partial shade. Like many other acacias, they’re typically quite drought resistant, once established.

4. Monkey Puzzle Tree (Araucaria araucana)

The monkey puzzle tree is one of the most unusual-looking and eye-catching trees around. It is a little larger than most trees used for ornamental purposes – it can grow to 80 feet in height or more – but it is a great addition to large yards and properties. And, like the other trees on this list, it won’t create serious litter problems. The monkey puzzle tree will tolerate light shade, though it prefers full sun. It isn’t a particularly drought-tolerant tree, but it will tolerate a wide variety of soil types. It’s also fairly salt-tolerant, so it will work well for homeowners living near the coast.



If you have a tree that is creating litter problems in your yard and you’d like to replace it with one that won’t cause such a mess, give your friends at Evergreen Arborist Consultants a call. We’ll have one of our certified arborists visit the property, examine the troubling tree and recommend a prudent course of action. In some cases, we may even be able to recommend ways to reduce the litter-related problems.

Five Deer-Resistant Trees for Southern California Properties

Deer are certainly lovely animals, and most people enjoy getting a glimpse of these beautiful creatures sauntering through their yard. Unless that is, the deer are destroying the plants and trees you’ve gone to the trouble and expense of installing on your property. In such cases, deer can represent quite a problem.

Short of building a large fence or getting a big dog to patrol your property, there aren’t many great ways to exclude the deer from your yard. If you provide a good food source for the deer, they’ll usually go out of their way to take advantage of it.

Accordingly, the best way to deal with deer and to protect your trees is by installing deer-resistant species, which do not appeal to the antlered animals. In fact, you can often use deer-resistant species to help protect any palatable species present, by planting the resistant species around the perimeter of your yard.

Fortunately, there are a variety of deer-resistant tree species that are suitable for southern California properties. We’ll describe five of the best below.

1. California Ash (Fraxinus dipetala)

Deer find most ash trees unpalatable, and most will thrive on properties with heavy deer traffic. But, because it’s always a good idea to opt for native species whenever possible, the California ash is a great deer-resistant choice for local properties.

A relatively small tree, the California ash rarely exceeds 25 feet in height, so it is suitable for most small- to medium-sized planting locations. It is also tolerant of droughts once established, and its root system rarely causes many problems. And while deer don’t find the leaves palatable, many other wildlife species – including bees and birds, among others – are attracted to ash trees.

2. Fuchsia Eucalyptus (Eucalyptus forrestiana)

Many eucalyptus trees reach incredibly large sizes and cause a variety of problems for homeowners and property managers, but the fuchsia eucalyptus is a modest-sized tree, which typically remains below 15 feet tall. Like most other eucalyptus species, the fuchsia eucalyptus produces buds, leaves and fruit which are not palatable to deer.

The fuchsia eucalyptus produces very attractive, inch-and-a-half-long, red and yellow flowers in the summer. These soon turn into dry-shelled fruit, which may cause minor litter problems when they fall from the tree; but, they won’t attract deer. These trees will thrive in a variety of soil conditions, and, although they prefer areas with full sun exposure, they can survive in partially shaded areas too.

3. Monkey Puzzle Tree (Araucaria araucana)

If you are looking for something that’ll stand out and catch the eye of every passerby, the monkey puzzle tree is hard to beat. The first thing most people will notice about the monkey puzzle tree is its tightly-packed, sharply triangular, evergreen leaves. However, it’s open canopy and sometimes-peculiar branching habit also attract plenty of attention.

Native to Chile, the monkey puzzle tree is an evergreen species, which retains its foliage all year long. These are very large trees, which occasionally reach 80 or 90 feet in height, so they aren’t appropriate for small planting spaces. They can grow in a variety of soil types, but they do require relatively high levels of soil moisture to thrive.

4. Vine Maple (Acer circinatum)

Another California native, the vine maple is quite similar to the Japanese maple (Acer palmatum), and it prefers the same types of cool and moist growing spaces that its more widely celebrated cousin does. The vine maple will not tolerate alkaline soils very well, nor will it grow well in compacted, clay-rich soils. It may also require supplemental water during dry summers.

The vine maple typically grows as a multi-trunked tree or shrub, and it rarely exceeds 20 feet in height and width. Accordingly, they are often used as small ornamental trees around shaded backyard decks or small streams. They shed a ton of dry fruit, which some owners find irritating, but they provide very attractive fall foliage, which may make them worth the trouble.

5. Korean Fir (Abies koreana)

Perhaps best known for their attractive upright cones (which are often purple to blue in color), the Korean fir is an excellent option in areas with dense deer populations. You’ll surely notice plenty of birds, squirrels and chipmunks living in and around Korean firs, but deer do not find their needles or cones tasty.

Reaching about 30 feet or so in height and 10 to 20 feet in width, these trees produce extraordinarily dense, conical canopies. This makes them excellent choices for screening projects, as they can discourage foot traffic, reduce highway noise and block prying eyes. They can thrive in full sun or partial shade, but they do require relatively moist soil. Unfortunately, Korean firs are somewhat susceptible to aphids.


If you need help protecting your property by installing deer-resistant trees, contact your friends at Evergreen Arborist Consultants and let us help. We can not only help you select the species that are most likely to survive in your yard, but we can assist in the installation process as well. We can even determine if you should have some of the trees that are attracting the deer removed.

Five Great Trees for Helping Your Local Honeybees

Hymenopterans – a group of insects that includes wasps, ants and bees – are incredibly important components of most terrestrial ecosystems. They not only serve as important food sources for predators and hosts for parasites, many of them play important roles in the process of pollination.

And while all pollinators are important for the plants on which they feed, honeybees are among the most important from a human perspective, as they’re used to pollinate a number of very important fruit crops. But unfortunately, honeybees have been dying off at an alarming rate thanks to something called colony collapse disorder.

The root causes of colony collapse disorder are varied and complex, and scientists are still working to identify the most important factors. Pesticides likely play an important role as do parasites and diseases, but it is quite possible that food availability is also part of the problem. And while the average citizen can’t do much to combat the first three problems, food availability is something they can help change. All you have to do is plant a few trees that provide the nectar honeybees need.

Honeybees feed on a number of different nectar sources, but the following five are among their favorites:

1. Bee Bee Tree (Tetradium daniellii)

It isn’t clear whether the bee bee tree is named for its bee-attracting nectar, but it would certainly make sense if that were the case. The bee bee tree (and its close relatives, which all appear to be very popular among honeybees) hails from East Asia, reaches about 60 feet in height and prefers to grow in areas with plenty of sun exposure. They grow quite quickly and produce pretty white, yellow or pink flowers in mid- to late-summer.

2. American Basswood (Tilia americana)

The American basswood (or American linden, as it is sometimes called) is a relatively large deciduous tree, which typically reaches heights of 60 to 100 feet. It is one of America’s fastest growing hardwoods, so it is popular among homeowners who want to add large trees to their property as quickly as possible, but it still takes about 10 years to begin producing flowers. Basswoods produce small, delicate-looking whitish flowers in mid-summer.

3. Willows (Salix spp.)

Collectively, willows are some of the favorite food sources of bees. However, because willows typically bloom in the very early spring, bees are seldom able to feed on them to the extent they would like, as the low temperatures prevent the insects from flying. However, this is less of a problem in southern California than it is in other places. There are many popular willow species and cultivars available, and several will work well in our region. Just be sure to avoid planting them near sidewalks, homes or other structures, as they frequently produce problematic roots.

4. Maples (Acer spp.)

Maples produce relatively inconspicuous flowers (which vary in color from one species to the next), but bees seem to find them without much trouble. However, most maples bloom in the spring, so they often present some of the same challenges that willows do. Maples have plenty of other things going for them, but perhaps no characteristic is as famous as their fantastic fall foliage, which comes in red, orange and gold flavors, depending on the species and cultivar selected.

5. Tuliptrees (Liriodendron tulipifera)

Tuliptrees are native to the southeastern United States, but they’ll grow in western locations that have sufficient soil moisture. They serve as one of the most important food sources for the bees living near them, but they require a very large planting space, as they are among the biggest trees in the country. Tuliptree flowers are quite pretty and resemble tulips (hence their colloquial name), but they are unfortunately limited to the upper canopy in most cases, so they’re difficult to appreciate.


If you’d like to help out the local honeybees and are interested in installing a few bee-friendly trees, contact your friends at Evergreen Arborist Consultants. We’ll send over one of our friendly and experienced arborists to assess your property and recommend a few of the best choices for the local conditions. With a bit of planning and a little effort, you can begin helping support the local honeybee population in no time.

Five Bad Trees for Allergy Sufferers

Many of the most popular trees — including magnolias, crepe myrtles and jacarandas, among others — have very attractive flowers. But while these flowers may smell nice, attract wildlife and beautify your property, other flowers can cause problems – particularly among allergy sufferers.

Many tree flowers produce allergenic pollens, which can leave sensitive individuals sniffling and sneezing for the entire blooming season. But surprisingly, many of the worst offenders don’t even have very showy flowers; they’re wind-pollinated species, who cast their pollen far and wide, causing it to cover everything in its path.

And while different people react differently to different types of pollen, the following five species are among the most likely to cause significant allergy problems. You’ll notice that most have relatively small, inconspicuous flowers, and rely at least partially on the wind to spread their pollen.

1. Maples (Acer spp.)

Maples are some of the few trees that cause significant problems for allergy sufferers yet are pollinated in large part by bees. Maples bloom early, so they are most problematic during the period between late January and early March. Maples are very popular, and they colonize new lands very easily, which means that they are pretty hard for allergic individuals to avoid.

2. Arizona Cypress (Cupressus arizonica)

It’s rather unfortunate that the Arizona cypress is such a problem for many allergy sufferers, as it is quite a nice tree. A grey- to blue-green conifer that reaches 70 feet in height or more, these trees look great in most yards and can be incorporated into screening projects with ease. There are a number of cultivars of the Arizona cypress available, so you can select from several different color forms and growth habits to suit your tastes and the space available.

3. Willows (Salix spp.)

Another group of early-blooming trees, willows usually release an avalanche of pollen from their drooping catkins in January and February, although the bloom can last until May in some places. Like maples, willows are often popular with bees, but they also rely on wind to help cross-pollinate and perpetuate the species. Willows can cause problems for underground pipes and structures where they grow, so there are often multiple reasons to consider removing these trees if you didn’t deliberately plant them yourself.

4. Mountain Cedar (Juniperus ashei)

The mountain cedar is one of the worst allergy offenders in the southwestern United States. Technically junipers, rather than cypresses, these trees are conifers, which don’t produce true flowers at all. Nevertheless, they still produce copious amounts of pollen, which they release into the air en masse. Mountain cedars release their pollen in December and January, and it can cause sufferers to be miserable for this entire time.

5. Elms (Ulmus spp.)

Elms have quite a history in America, and despite problems with Dutch elm disease, there are still plenty of elms growing in residential yards, commercial lots and wild areas throughout several parts of the country. Elms typically bloom – and therefore cause the biggest problems for allergy sufferers – in the early spring, with the peak season occurring in late March and early April. However, the precise blooming period varies from one elm species to the next.


If you are worried that some of the trees in your yard are wreaking havoc on your eyes, nose and throat, give your friends at Evergreen Arborist Consultants a call. One of our trained arborists will visit your property, identify the local trees and point out any that may be problematic. And if you decide that you need the tree removed, we’ll be happy to provide assistance in this regard too.

The Year-Round Benefits of Conifers

Residents of Malibu, Laguna Beach, Beverly Hills and the rest of the greater Los Angeles area are fortunate to have so many tree options available to them. A number of fantastic trees are native to our portion of the state, and a dizzying number of exotic species adapt well to our local climate.

But many people find the lure of beautiful flowers and glorious fall color irresistible when picking out trees for their new installation. This leads them to select broad-leafed hardwoods, such as maples, redbuds, elms, oaks and others, rather than needle-leafed conifers, such as pines, hemlocks, redwoods and firs.

This is a shame, as conifers provide a number of great benefits for homeowners and property managers. One of the most important benefits, and the one on which we will concentrate today is the fact that most conifers are evergreen (although bald cypresses and a few others do shed their leaves in the winter).

By contrast, most broad-leafed trees shed their leaves every winter. Additionally, some broad-leafed trees are facultatively deciduous, meaning that although they “want” to keep their leaves all year long, they may shed them in response to drought or other environmental stresses.

Some of the benefits evergreen conifers provide include:

Wind Screening

Because most conifers retain their leaves all year long, they make excellent choices for wind-screening projects. Shielding your property from winds can help to reduce the evaporation rate, which will help your soil retain moisture better than places exposed to constant winds. And don’t forget that dense conifers also help shield your property from anything the wind is carrying, such as dust and grit.


Those living in the northeastern United States often prefer installing deciduous hardwoods specifically because they shed their leaves in the winter. This allows them to enjoy shade in the summer and plenty of sun exposure during the winter. But here in southern California, you don’t have to maximize your sun exposure to keep Jack Frost at bay. In fact, it is more likely that you’ll want the benefits of shade in all seasons.

Wildlife Habitat

Many deciduous trees are quite important for wildlife; oaks, hickories, beech trees, for example, provide significant quantities of food for local songbirds and small mammals. Some animals even take shelter inside cavities made within these trees, or make their summer homes amid the dense and concealing canopy. However, because this canopy disappears in the summer, many birds and tree-dwelling mammals prefer to reside in conifers all year long. Some birds even preferentially nest in specific conifer species.


Your desire for privacy probably doesn’t change with the seasons, and neither should the trees you use to provide that privacy. A nice hedge of arborvitaes, for example, will remain thick, lush and visually impenetrable all year long, while a row of maples will expose your property to anyone driving by once November rolls around.


Of course, there are plenty of other benefits various conifer species provide. Some, such as pines, provide important food sources for your local critters, and others, like Korean firs, are simply gorgeous, and immediately become the centerpiece of any property. No matter which conifers you select for your yard, just be sure to consider the local conditions and the space you have available (some conifers grow quite large).

If you’d like some help picking out and installing some conifers for your property, reach out to your friends at Evergreen Arborist Consultants. We’ll help guide you through the process in every way, including species and site selection, installation and follow-up care. Most homeowners and property managers can complete all of these steps on their own, but it never hurts to have some help from arborists with more than 28 years of experience.

The Iconic Jacaranda Trees of Long Beach

The jacarandas of Long Beach are among the most iconic trees in southern California. In addition to growing well in the climate of the area, they are some of southern California’s most eye-popping trees – at least for a month or so. But even for all of the beauty and benefits they provide, some residents wish the jacarandas would all go away.

Jacaranda Basics

Blue jacarandas – known to botanists and arborists as Jacaranda mimosifolia – originally hail from central South America, but they’re currently cultivated in suitably warm climates all over the world. They do not tolerate freezing temperatures well, but hardy, established trees often survive temperatures as low as 20 degrees Fahrenheit.

Jacarandas occasionally reach about 60 feet in height or so, and they often develop a round or vase-shaped canopy. Because of their typical growth habit, they were often planted on both sides of a street, which creates something of a closed canopy.

Jacarandas grow best in areas with deep, fertile soils, and plenty of direct sunlight. Because they do not tolerate excessively dry soil, it is important to provide supplemental irrigation during dry spells. Additionally, you’ll want to provide this water in the appropriate manner (high quantity / low frequency) so you can encourage the development of deep root systems.

The Magical Month of May

Despite their many positive traits that led to their popularity, jacarandas are most famous for their glorious blue flowers which usually burst forth in late April or May. During this time, the purple-blue flowers dominate the landscape and create a truly amazing aesthetic that lasts for about a month or two.

The individual flowers grow to about 2 inches in length and are borne on foot-long panicles (stalk-like structures). A number of bee species are attracted to the fragrant, trumpet-shaped flowers, where they assist in pollination duties.

A Love-Hate Relationship

It is hard to argue that jacarandas in bloom are jaw-droppingly beautiful. But soon enough, the flowers will have served their purpose, and the trees will begin carpeting the ground in blue petals as the fruits begin to mature. Given the high number of flowers on jacaranda trees, this causes quite a mess.

Homeowners living under jacaranda canopies frequently complain about the shed petals, which end up everywhere. They fill up rain gutters, cover up drainage grates and find their way into homes, where they may stain light-colored carpets. Some residents are even forced to use blowers to clear away the thick layer of petals covering their property.

But this frustration eventually comes to an end, as the petals finally disappear, and the jacarandas fill their canopies with gorgeous green, feathery foliage. And this causes many to forget about the headaches they briefly cause after flowering until a year passes, and they’re faced with another mess to clean up.


If you need help caring for your jacaranda trees, or you are considering installing some on your property, give your friends at Evergreen Arborist Consultants a call. Jacarandas grow really well in Long Beach, Beverly Hills, Santa Monica and the rest of the greater Los Angeles area. Let us help beautify your yard today!

Alex Shigo: The Father of Modern Arboriculture

No matter the field, subject or industry in question, it is always important to understand the role important predecessors played in shaping the world modern world.

For example, horn players should learn about Miles Davis; baseball players should learn about Mickey Mantle and Babe Ruth;and artists should learn about Picasso, Da Vinci and Dali.

But if you are an arborist, tree-care professional or simply someone who loves to learn about trees, you should familiarize yourself with the work of Alex ShigoPh. D. – better known as the father of modern arboriculture.

The Early Years

Alex Shigo was born in Duquesne, Pennsylvania in 1930. He was a talented and dedicated musician from an early age, who played clarinet for the official United States Air Force Band as part of his service during the Korean War. After the war was over, he enrolled in Waynesburg College, where he eventually obtained a Bachelor of Science degree in biology. Soon after, he was admitted to West Virginia University, where he obtained both a Master’s and Doctoral Degree in plant pathology.

Career Path

In 1960, Dr. Shigo was hired to perform tree pathology work for the U.S. Forest Service. Dr. Shigo stayed with the forest service for 25 years, before he retired and began working as an author and lecturer, sharing his knowledge of trees with all who cared to listen or read. A prolific writer, Dr. Shigo authored and co-authored 160 different books, academic papers and popular pieces during this time.

Major Contributions to Arboriculture

A pioneering thinker in the world of tree science, Dr. Shigo turned many time-honored tenants of tree care on their head. Dr. Shigo’s contributions to the world of arboriculture could fill volumes, but a few of his most important lessons and breakthroughs include:

  • In the 1950s, Dr. Shigo began using a newly available technology – the one-person chainsaw – to learn more about trees. During this time, Dr. Shigo dissected more than 15,000 trees to better appreciate their biology. Researchers had already been carrying out tree dissections for many decades, but most of these dissections were carried out on in a crosscut-manner. By contrast, Dr. Shigo began dissecting trees along their vertical axis, which revolutionized our understanding to the spread of decay through a tree.


  • Thanks in part to these dissections, Dr. Shigo re-wrote our understanding of tree wounds. Specifically, he argued that trees do not heal – they seal up wounds and grow around them. He coined the term CODIT (Compartmentalization of Decay in Trees) to help explain this process and allow tree-care professionals to benefit from the knowledge.


  • Shigo studied the way trees in the forest shed their branches, and compared this with what he learned from his study of decay. In doing so, he realized that the flush-cutting technique preferred by arborists at the time was not the best way to prune trees. Instead, he championed the importance of leaving the branch collar intact, and invented the tree-cut pruning technique, which prevents stripped bark and damaged branch collars.

Dr.Shigo continued to learn about trees and share his considerable knowledge about them for the rest of his life. He died unexpectedly after suffering a fall on October 6, 2006, at the age of 76.

Try to keep Dr. Shigo’s contributions to arboriculture in mind the next time you find yourself looking at a beautiful urban forest. Thanks to his work, those trees will feature full, vibrant canopies and properly trimmed stubs – and they’ll be healthier and more attractive for it.



Smoketrees (Cotinus spp.) derive their common name from their wispy, filamentous flowers, which appear like puffs of smoke when viewed from a distance. Because they are very easy to grow and add unique beauty to suburban landscapes, smoketrees are very popular ornamentals, often planted as borders or hedges.

A Tale of Two Species

While both American (Cotinus obovatus) and European smoketrees (Cotinus coggygria) are rather similar, they do exhibit their share of differences.

American smoketrees typically grow slightly larger than the European species do, in terms of both height and spread. They also feature larger leaves than their European counterparts, but the European species usually bears denser flower heads than American smoketrees.

While the two have different geographic ranges (American smoketrees grow throughout the southern United States, while European smoketrees are found through southern Europe, east as far as the Himalayas), they are both commonly planted in each other’s respective range. However, European smoketrees are the more commonly used ornamental of the two species and they are available in a greater number of cultivars.

Traits of the Trees

Smoke trees can reach heights of 20 to 40 feet, but many are little more than shrubs and few reach heights greater than 15 feet. Their flowers grow as 6- to 12-inch-long panicles, which vary from pink to white in color. Most pollination probably occurs with the help of insects, such as bumblebees. Because most of the nectar produced by smoketrees is easy to access, a wide variety of insects feed upon them.

Smoketrees first bloom in the spring, but they can continue bloom for the duration of the summer. Once cross-pollinated, smoketrees produce small, dry fruits, technically termed drupes. The fruit do not appear to have a significant value to wildlife, nor do they cause a substantial litter problem.

In addition to their beautiful flowers, smoketrees often bear attractively colored leaves, which are particularly gorgeous in the autumn, when they turn brilliant red, yellow or purple. Smoketrees also bear exfoliating bark and – at least on older specimens – twisted, gnarled trunks, giving the trees further visual appeal.

Simple Soils

Unlike many other trees and shrubs, which thrive in highly fertile soils, smoketrees often grow best in relatively infertile soils. While they will grow quickly in fertile soils, this tends to shorten their lifespans.

Additionally, those grown in highly fertile soils tend to produce a less-attractive, sparse growth habit, rather than the compact, dense habit attained by those grown in infertile soils. Aside from those that are too fertile, smoketrees adapt well to most soils. They exhibit moderate drought tolerance, but can also cope with periods of intense rain.

Smoketrees in Southern California

Most authorities recommend planting smoketrees in USDA Hardiness zones 5 through 8, but smoketrees usually thrive in southern California landscapes. Few smoketrees succumb to pests, although they are susceptible to Verticillium wilt. Smoketrees require relatively little supplemental irrigation and they are rather drought tolerant. The plants work well in relatively small areas, and they rarely produce damaging surface roots.

Much of their size and growth habit depend upon how they are maintained – some homeowners prefer for the plants to take on a tree-like form, whereas others prefer to keep the trees small and shrub-like. Some even coppice the trees, causing them to produce a flourish of dense, young growth. However, this practice reduces the number of flowers that develop in the coming season.

Cultivars featuring dark leaves and bright pink to purple flowers are particularly favored by gardeners and homeowners.

Trees in Downtown Chicago

Trees and Healthy People – No Appointment Necessary

Trees, parks, and gardens are not just simply considered beauty in the city but as a matter of improving public health. There is a link between an individual’s socio-economic position and their health is well-established. Epidemiological studies show a positive relationship between longevity and proximity to green space. Fewer people die of asthma and heart disease in Chicago, Los Angeles, and other U.S. cities when trees and other greenery are present. A single tree cleans the air because of a tree’s ability to absorb tiny smog and soot particulates. Trees also provide shade which block ultraviolet rays that contribute to skin cancers. Another health benefit of evergreen trees can be found by patients in hospitals with views of trees and gardens outside their window who recovered faster after surgery.

Brief encounters with nature make people happier, reduce chronic stress that leads to ill health and help both adults and children (including kids with ADD) focus better on mentally taxing tasks. Exposure to green surroundings reduces mental fatigue and irritability. The ability to concentrate is increased by green views, along with the ability and willingness to deal with problems thoughtfully and less aggressively.

A 2011 study in the Amercian Journal of Epidemiology found that vandalism and gun assaults and stress levels decreased in greener environments. In a study conducted in a Chicago public housing development, people who lived in apartment buildings with trees and greenery immediately outside reported fewer aggressive and violent acts than those living in barren but otherwise identical buildings. In addition, the people in greener surroundings reported a smaller range of aggressive tactics during their lifetime.