Small Leaves, Light Shade; Big Leaves, Deep Shade

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The shade under these fine-leaved honeylocust (Gleditsia triacanthos ‘Sunburst’) is very light and the lawn grows as well as in full sun. Source: oregonstate.edu

If you want to plant a tree on your property, but don’t want to give up a sunny flower bed or lawn because of the shade the tree will create, consider the following detail: the smaller the tree’s leaves, the more light will filter through; the bigger they are, the less sun reaches the ground.

Therefore trees with tiny leaflets, like honey locust (Gleditsia spp.), black locust (Robinia spp.) and silk tree (Albizia julibrissin) and trees with deeply cut leaves, like  cut-leaved alder (Alnus glutinosa ‘Imperialis’), certain Japanese maples (Acer palmatum dissectum) and cut-leaf birches (Betula pendula ‘Filigree Lace’ and others), let in plenty of light and you can consider the space at their feet as being in very light shade and sometimes, when there are no other obstacles around, the equivalent of full sun.

The opposite is true of trees with very large leaves, like Norway maple (Acer platanoides), basswood (Tilia americana) and red oak (Quercus rubra). They create deep shade, even when they’re young and the shade just keeps getting deeper as they mature. Growing flowers or lawns at their base can be very difficult indeed.

Most other trees have “average-sized” foliage and will give medium shade in their youth, but tend towards deep shade as they mature.

In Praise of Tall Trees

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This is what the suburbs used to look like: modern developments however are sadly lacking in big trees. Photo: Fgrammen, Wikimedia Commons

An important element of residential landscaping seems to be going the way of the dodo in modern cities. Tall trees — the big, majestic ones that gave the landscape its character — are increasingly being left out in favor of smaller trees or even shrubs grafted on short trunks.

This is a fairly recent trend. If you look suburban developments over 60 years old, tall tree species dominate. Big maples and huge majestic oaks are everywhere. They helped create an atmosphere of tranquility and well-being. Take a walk in a neighborhood 40 years old or less, though, and you mostly see green lawns and shrubs, maybe a flower bed or two, and a few smaller trees you couldn’t even fit a lawn chair under, but not many larger ones. True enough, a somewhat sparse landscape can be still attractive, but it tends be so in a cold and impersonal way. Such neighborhoods aren’t really inviting. It’s as if the residents planned all along to leave their dreary home landscape on weekends for a break at the cottage … surrounded by tall trees, of course!

Just Don’t Think About It, Plant Them!

Why do larger trees deserve a place in suburban and urban lots?

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Taller trees create a homey, friendly, inviting atmosphere. Photo: Bridan Stansberry, Wikimedia Commons

First, for the shade they offer. Gardeners may complain you can’t grow anything under big trees (actually, you most certainly can: I’ve written an entire book about shade gardening, so I know it’s far from impossible!), but the fact is we’re attracted by shade. During the dog days of summer, a neighborhood well decorated with broad, shade-producing trees is livable; one denuded of any tall vegetation simply is not.

Also, human beings, by their very nature, seem to need trees in their surroundings. Is this a reminder of the long distant past when our ancestors took refuge in trees when they were attacked by predators? No one knows. Still, the feeling of peace and security that emerges from a big tree seems very real. In fact, it can be seen in different cultures all over the world: when people are given a choice of where they would like to live, they inevitably prefer not a forest, but a landscape dotted with mature, tall trees.

Of course, maybe you do feel you have trees on your property. But can you really call a small weeping tree barely 10 feet (3 m) high a tree? Or a flowering crabapple or a Japanese lilac or one of the many other “small trees” so heavily planted these days? They may be trees by definition, but you can’t walk under them without bumping your head, you can’t fit a lawn chair underneath them without your legs sticking out in the hot sun and they don’t create the atmosphere of permanence and security that large trees can provide.

How to Use Trees Wisely

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Bravo: this modern homeowner has included one tree that will reach a reasonable size. But look at the photo: wouldn’t it be more attractive with at least one tall tree reaching up from the back yard as well?

Ideally, to recreate the sense of peace and permanence you want, you’d need at least one large tree per yard. Preferably two, in fact, on in the front and one out back. Obviously, the larger the lot, the more trees it needs.

In addition to the atmosphere they create, big trees offer other advantages:

  • Reduced cooling costs in the summer;
  • Reduced heating costs in winter;
  • Minimal maintenance;
  • Increased land value;
  • An environment healthier for human physical and mental well-being;
  • An inviting landscape for our feathered friends;
  • And much more.

Trees have certain disadvantages, of course, but these are generally easy to overcome.

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Planting a tree takes a bit of effort. Photo: Maryland GovPics, Flickr

Planting them, for example, is fairly arduous … but at least you only have to do it once!

The shade they produce will reduce the choice of plants that will grow underneath, but there is still a good choice of shade plants. Where it’s too shady for a dense lawn, for example, there are dozens of equally dense, maintenance-free groundcovers.

Some trees do produce seeds or fruits that can be briefly annoying when they fall, but there are many cultivars that are either sterile or male (male trees produce no seeds).

Finally, there will be leaves to rake up each fall — yes, even so-called evergreens tend to lose leaves at that season —, but fortunately that’s only a once-a-year thing … much less work than maintaining a lawn, which usually requires weekly mowing.

Plant Tall Trees Where They Can Reach Their Full Size

When planning to buy a tree, ask about its maximum height and spread and use that info to find a suitable location. For example, don’t plant it where it can interfere with overhanging wires, too close to the house, or directly in front of a window. Nor should it reach over into a neighbor’s lot, otherwise there is a serious possibility of conflict.

Lots of choice!

What follows are some suggestions of tall trees (over 30 feet/9 m) that can decorate your property. All are low- to no-maintenance trees that will enhance your property’s value.

Note that the trees shown here were chosen for a cold climate region. In areas with more temperate or even warm climate, you’ll have an even greater choice. Measurements are averages reached under normal growing conditions.

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Red maple in its fall glory. Photo: Famartin

Red maple (A. rubrum): Long neglected by arborists, this North American native is becoming more popular, especially in colder climates. Its bark, smooth and pale gray in its youth, becomes rough over time. Its three-lobed leaves turn bright red in autumn. Prefers moist growing conditions. Height: 60 feet (18 m). Spread: 50 feet (15 m). Hardiness zone: 3b. There are also smaller, more symmetrical selections, such as ‘Morgan’ (50 x 50 feet/15 x 15 m) and ‘Red Sunset’ (30 feet x 20 feet/9 x 6 m). ‘Autumn Flame’ (35 x 20 feet/11 x 9 m) is the best choice for colder climates (zone 3).

Freeman Maple (A. x freemanii): This hybrid maple results from a cross between red maple and silver maple (A. saccharinum), but is closer to red maple in overall habit. It’s perhaps even superior to red maple as a city tree and is even a bit hardier: zone 3. There are several cultivars, including Autumn Blaze (‘Jeffersred’), 50 x 30 feet/15 x 9 m), which turns fiery red in the fall.

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The orange-red fall color of the sugar maple. James St. John, Flickr

Sugar maple (Acer saccharum): It used to be that arborists shunned this North American native, considering it unsuited to urban areas, and recommending Norway maple (A. platanoides) instead. Nowadays, attitudes have changed and that there are few situations where a sugar maple wouldn’t be considered a better choice than its Norwegian relative. Planted in isolation, it takes on a beautiful speading, rounded shape quite unlike its fairly scrawny appearance in forested areas. With its excellent orange-red fall color, it’s also much more colorful than Norway maple and less subject to winter damage. Plus its smaller, rapidly decomposing leaves have less tendency to choke out grass. Finally, it isn’t subject to tar spot disease, this disease which turns the leaves of Norway maple into an unsightly mess. Both, however, do have dense and shallow roots: there’s no denying that maintaining a perfect lawn under either maple is a challenge, though. Height: 60 ft (18 m). Spread: 40 feet (12 m). Hardiness zone: Zone 4. There are several horticultural selections, including ‘Green Mountain’ and ‘Legacy’, which offer a more regular habit on a somewhat smaller tree than seed-grown sugar maples.

Common Hackberry (Celtis occidentalis): This North American tree looks a bit like an elm but with a more rounded crown. Corklike bark. Yellow color in autumn. Height: 65 feet (20 m). Spread: 50 feet (15 m). Hardiness zone: 4.

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Ginkgo starting to take on its fall color. Photo: Crusier, Wikimedia Commons

Ginkgo (Ginkgo biloba): Very slow growing, but totally resistant to insects and diseases. Attractive yellow foliage in the fall. Always ask for a male specimen: the females drop messy, stinky fruits. Height: 45 feet (14 m). Spread: up to 40 feet (12 m), but much narrower than wide for the first 60 years or so. Hardiness zone: 4.

Honey Locust (Gleditsia triacanthos inermis): Tree with an open, often irregular crown that lets sun through. Rough bark. The compound leaves are composed of leaflets so small that they decompose quickly: you don’t even have to rake them up in the fall! The extremities of the branches often freeze during the winter in colder climates, but that doesn’t really affect its appearance. Look for the cultivars ‘Moraine’ and ‘Skyline’, as several honey locusts, like ‘Sunburst’, are too small to make good shade trees. Height: 65 feet (20 m). Spread: 55 feet/17 m. Hardiness zone: 4b. ‘Northern Acclaim’ is an extra-hardy variety: zone 3.

Amur Cork Tree (Phellodendron amurense): Little known, but very attractive and virtually without cultural problems. The bark on mature specimens is very corklike. Height: 40 feet (12 m). Spread: 40 feet (12 m). Hardiness zone: 3.

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Siberian pear is an easy-to-grow, heavily blooming tree well worth discovering. Photo: Sten Porse,  Wikimedia Commons

Siberian Pear (Pyrus ussuriensis): A large tree that dwarfs its smaller fruit tree cousins: apples, plums, cherries, etc. It’s also essentially immune to most of the diseases and insects afflicting fruit trees. It blooms abundantly in spring, covering itself with white blossoms, but its tiny fruits are of no interest to humans, although they do attract birds and small mammals. It will only bear fruit if there are two different clones in the area, since cross-pollination is obligatory for this species. Height: 40 feet (12 m). Spread: 33 feet (10 m). Hardiness zone: 3.

Oaks (Quercus spp.): A large group of trees, most tall and spreading, generally with toothed leaves. They’re considered among the most majestic of trees, but their growth is fairly slow, at least after the first 10 years or so. Height: 65 feet (20 m). Spread: 50 ft (15 m). Hardiness zone: generally, zone 4. Red oaks (Q. rubra) and scarlet oaks (Q. coccinea) are particularly interesting for their massive shape and fall color. Where space is limited, consider columnar English oak (Q. robur ‘Fastigiata’) which reaches the same height as the other oaks but rarely exceeds 13 feet (4 m) in diameter. The best oak for cold climates is bur oak (Q. macrocarpa), hardier than the others: zone 3. Shingle oak (Quercus imbricaria) is unusual among hardy oaks in that it has narrow untoothed leaves.

Think-Twice Trees

The following trees may be useful in some cases … but have problems that can seriously reduce their usefulness under certain circumstances. It’s up to you to decide whether they are worth growing under your conditions!

Horse Chestnuts, Hickories, Walnuts (Aesculus spp,. Carya spp., Juglans spp.): They make beautiful trees, but their large fruits can be an annoyance, especially near roads. In addition, walnut trees are allelopathic (toxic to plants that grow at their base).

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River birch

Birch (Betula spp.): Most make very nice trees, with attractive bark, but they’re often short-lived (especially silver birch [Betula pendula] and its varieties) and rarely make it to their full size. In addition, they are susceptible to a wide range of diseases and insects and that can mean a lot of spraying … under some circumstances. Ask a local arborist their opinion, as the problems tend to vary greatly, from minor to major, depending on local conditions. One exception is river birch (B. nigra), especially the cultivar Heritage (‘Cully’), with bark that exfoliates gracefully: it’s long-lived and disease- and insect-free under most conditions. Height: 50 feet (15 m). Spread: 35 feet (10 m). Hardiness zone: 3.

Catalpa (Catalpa spp.): Although catalpas survive in cold regions and thus some nurserymen rate them as zone 4 trees, in fact, they tend to suffer severe winter damage in zones 4 and 5, at least periodically, and, as a result, grow very irregularly. With their abundant white to lavender blooms, they make an excellent choice in areas 6 and up, though. Height: 50 feet (15 m). Spread: 30 feet (9 m).

Linden (Tilia spp.): Tree with a strong trunk and heart-shaped leaves, plus highly scented flowers. The little-leaved linden (T. cordata) is very popular and offers many interesting cultivars, however … this genus is not a good choice in regions infested with Japanese beetles, as they literally defoliate the tree every summer. Height: 100 feet (30 m). Spread: 80 feet (25 m). Hardiness zone: 3.

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Ulmus x ‘Morton’ Accolade is a hybrid elm the looks like an American elm, but is resistant to Dutch elm disease. Photo: Bruce Marlin

Elm (Ulmus spp.): American elm (U. americana) almost inevitably falls victim to Dutch elm disease, which is difficult and expensive to fight. There are, however, several elms, including hybrid varieties, which share the American elm’s majestic upright spreading habit while showing good resistance to the disease. Before buying an elm, always ask if it’s resistant to Dutch elm disease. The Siberian elm (U. pumila) is resistant to Dutch elm disease, but is a weak-wooded tree with a poor growth habit and susceptibility to other diseases. Plus it self-seeds excessively and is considered an invasive species in many areas.

Trees to Avoid at All Costs

Ash (Fraxinus spp.): The arrival of the emerald ash borer (Agrilus planipennis), a deadly tree-piercing insect, in North America—and even now in Europe—has killed pretty much any interest in this formerly popular street tree. You might want to maintain the ones you have, but it’s probably wise to avoid planting new specimens.

Poplars, Willows, Silver Maple (Populus spp., Salix spp., Acer saccarhinum): The roots of these fast-growing trees are extremely invasive and often cause damage to domestic and municipal water and sewage pipes. They often also sucker extensively or self-sow and so become very invasive. It’s illegal to plant these trees in most municipalities.


There you go: a list of big and beautiful trees you might want to consider growing. And don’t delay, as it will take a few years before you can savor their full effect on your property!20170528B Fgrammen, WC

Yes, You Can Compost Diseased Leaves

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This is a repeat… but I’ve had 2 questions on the subject over the last week, so obviously there’s a need to release the information a second time.

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One hears the strangest things out of the mouth of “experts” sometimes. One of the stupidest is that you must never recycle diseased leaves, such as those with tar spot, powdery mildew or apple scab, for use in compost or in mulch. They insist you must either burn infested leaves or bag them and put them out on the street so the municipality can pick them up and destroy them.

Now this seems to make sense. By destroying leaves bearing the spores of a disease rather than recycling them as mulch or compost, which doesn’t always do the job, won’t you help control the disease? Actually, there is no proof that this makes one iota of difference.

For leaf diseases already present throughout a region, the horse is already out of the barn, so to speak. The disease is out there and unless you destroy every single infested leaf (which is nigh to impossible), you will never be able to control it. It only takes one spore-bearing leaf to infect a hundred plants… and no cleanup campaign will ever get every single leaf throughout a region. Having big trucks haul the leaves away for burning is simply polluting the air for nothing. When I hear the same town recommend, as mine does, recycling leaves on the one hand and not including diseased leaves in compost or mulch on the other, I always imagine the poor gardener, sitting on the ground sorting through thousands of leaves one by one!

This reminds me of the old belief that you had to burn the leaves and stems of mildewed phlox and bee balm (Monarda) each fall to prevent the disease from returning. I did this faithfully year after year and the disease came back every time. I even set one phlox plant ablaze one fall to see if that would work. The plant came back the next spring, but was as diseased as all the others by fall. I eventually found a technique that did work: I removed the disease-susceptible plants and replaced them with disease-resistant varieties. Problem solved!

Let’s get real! WIth wide-spread leaf diseases, the damage is already done. So why not use the affected leaves ecologically by recycling them as compost or mulch? Mother Nature has been doing this for millions of years: don’t you think she knows best?

Norway Maple: the Great Invader!

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Norway maple: a nice, symmetrical shade tree… but with a hidden vice!

Sometimes when you try to solve one problem, you create another. That’s what happened in the 1950s and 1960s with the massive introduction of the Norway maple (Acer platanoides) in Eastern North America. At that time, North America’s most popular street tree, the American elm (Ulmus americana), was being decimated by Dutch elm disease and people were looking for a substitute. The Norway maple, although largely untested, quickly became the street tree of choice. It was planted by the hundreds of thousands across North America and remains, in most areas, the tree most commonly sold in garden centers.

Many varieties of Norway maple have decorative leaves, like this purple-leave Acer plantanoides 'Schwedleri'.

Many varieties of Norway maple have decorative foliage, like this purple-leaved cultivar, Acer plantanoides ‘Schwedleri’.

It’s not an unattractive tree: relatively fast-growing, with dense, dark green foliage (or purple or variegated foliage in the case of some of its many cultivars) and a thick trunk. Also, it’s very tolerant of street conditions: air pollution, compacted soil, road salt, etc. It certainly looked like a good choice… at first. Over time, it showed more flaws: its dense root system uplifts and destroys sidewalks, it kills lawns and it suffers severe breakage during storms, causing untold millions of dollars of damage. Also, it turns out, for reasons unknown, to be relatively short-lived in North America: only about 50 to 60 years compared to up to 250 years in Europe. But who thinks that far ahead when planting a tree?

But the main problem turns out to be its invasive nature.

Who knew? In Central and Eastern Europe, where it is native, Norway maple is not an invasive species. It simply melds into the local forest, one tree among many. In Eastern North America, though, its seeds fall everywhere and germinate under a wide variety of conditions. And, unlike most other invasive introduced species, which tend mostly to stick to disturbed habitats, Norway maple quickly moves into and starts to dominate local forests, outcompeting native trees and especially its North American counterpart, the sugar maple (A. saccharum).

Sugar maple in its fall glory.

Sugar maple in its fall glory.

The sugar maple is the dominant tree in much of eastern North America’s climax hardwood forest, from Lake Superior to Pennsylvania (even further south in mountainous regions) and from the Eastern seaboard to the Prairies. It is well known as the source of maple sugar… and of the brilliant fall coloration that attracts so many tourists to the area in October.

 War of the Species

Norway maples produce huge seed crops, much greater than sugar maples, and their seeds, carried by the wind, tend move into maple forests where they grow readily. Their seeds are capable of germinating in deep shade, even more so than those of the sugar maple, although it too is highly shade tolerant. Norway maple seedlings grow quickly and densely and generally shade out any sugar maple seedlings that do sprout. They are more heat-tolerant that young sugar maples and thus better able to survive a climate influenced by global warming. As they grow, Norway maples create greater shade and drier soil conditions than native woodland species can tolerate, creating woodlands barren of undergrowth… other than more Norway maple seedlings! It is feared that, if the spread of Norway maples into the wild continues to be tolerated, they will create a dense monoculture, eliminating entire North American ecosystems.

You can see the signs already. In many neighborhoods, Norway maples sprout abundantly from hedges, along property lines, and pop up in shade borders. When the care in local parks is neglected, they move in and take over any areas that are not regularly clipped by lawn movers. And where city and suburb meet native woodland, the Norway maple is usually already established, slowly working on becoming the dominant tree.

In natural forests in Montreal’s Mount Royal Park, for example, Norway maple seedlings were found to outnumber sugar maple seedlings 4 to 1 in 2003 and it was estimated the species would dominate the park’s forest “within a generation”.

Some authorities have “seen the light” and banned Norway maples. It is illegal to plant them in Massachusetts and New Hampshire, for example, and many municipalities have similar laws. One major chain store, Meijer Garden Centers, has voluntarily removed the plant from its stores. Unfortunately, I know of no other nurseries that have followed suit and Norway maples remain widely available in most regions where they continue to be planted on a large scale.

It would be nice if more governments banned the tree… but they seem to be turning away from ecological issues these days. And I must admit I’m amazed and puzzled that garden centers continue to produce and promote Norway maples in areas where it could easily escape into native forests. The whole problem would be reduced considerably if shoppers were simply offered other trees instead. Most probably wouldn’t even notice the difference! I don’t think home owners set off to a nursery looking for a Norway maple; they’re looking for a “shade tree”, period, and would happily choose among whatever species are offered. No government ban would be needed if garden centers showed more concern about the environment!

Help from the Strangest Place

20150408HOddly, a plant disease may become a major player in the fight against the invasive Norway maple.

Tar spot disease (Rhytisma acerinum), a disease specific to Norway maples and certain other maples (but not the sugar maple*), has been in North America since at least the year 2000 and has spread throughout most of eastern part of the continent, especially over the last 5 years. It causes disfiguring dark black spots on Norway maple leaves, making the entire tree unattractive from midsummer until fall. No effective treatment for this disease is known other than removing the affected tree. Municipalities have been spouting nonsense about raking up and destroying leaves to reduce the effect of tar spot, but there is not one iota of proof that striving to pick up and destroy every single diseased leaf in the fall (it takes only one to cause the following year’s outbreak!) does anything other than annoy gardeners. For more information, see Yes, You Can Compost Diseased Leaves.

*There are other tar spot diseases that target the sugar maple, but they are not very common and tend to appear only sporadically and on a much more limited basis.

The more gardeners see this striking disease, which has turned entire city streets into something like a scene from a horror movie, the more likely they are to think twice about buying a Norway maple. Unfortunately, new leaves appear healthy, so during the prime season for selling trees, spring, even seriously contaminated trees show no symptoms. Still, as tar spot disease gets more and more press and the information circulates that the only real solution is avoid planting Norway maples, this can’t but help reduce Norway maple sales.

So, spread the word. Tell friends and neighbors not to plant Norway maples and, if you have that kind of influence, try to get your local government to ban planting them. Also, express your disapproval to the manager each time you see them in a local garden center. These measures may be little and late, but at least they’re a step in the right direction.

How to Distinguish Between Sugar Maples and Norway Maples