Sample text for Native trees, shrubs, & vines : a guide to using, growing, and propagating North American woody plants / William Cullina.
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Introduction
Plants have an ability that no animal does: they can, theoretically,
live forever. An orchid living in the duff on the forest floor simply
grows a complete new self each year — new roots, new stem, new
leaves, new flowers. Barring some catastrophe like a systemic disease
or the chomping jaws of a burrowing rodent, a herbaceous plant like
the orchid can go on this way for eons like the phoenix rising anew
from the ashes each spring.
Woody plants differ from herbaceous plants in that they
retain the same framework from year to year, pasting on a new layer
of living tissue over the dead bones of tissues past. Unlike the
orchid, a shrub or tree pastes on a veneer of new tissue atop those
preceding it. An old, massive oak is simply a thin, living skin
stretched over a long-dead framework of supporting wood. Woody plants
were the first master builders, laying down lignin and cellulose to
strengthen their stems and lift their leaves higher and higher above
other plants that would otherwise shade them, or browsers bent on
eating them. After the invention of photosynthesis — whereby leaves
manufacture carbohydrates from carbon dioxide, water, and light — the
invention of wood was the next great leap forward that allowed trees
and shrubs to dominate all the places where liquid water is abundant
enough to nurture their lofty canopies.
Inevitably, this very woody framework that is their strength is also
their undoing, as fungi, ants, and termites discover it and begin to
slowly but relentlessly undermine it from within. Trees do not die
quietly. Their bleached skeletons remain like whale bones on the
beach long after their living skin has withered. Colonizing plants
like box huckleberry and quaking aspen combine the strategies of the
oak and the orchid, outliving even the most ancient woody tree by
sending up new stems or trunks from a slowly spreading root system.
DNA testing has shown that individual colonies of aspen or
huckleberry, which may stretch over many acres, consist of a single
individual that has gradually been expanding over the last 10,000
years. Barring climate change or human interference, it could easily
go on for 10,000 more!
Woody plants have been called the "bones" of the garden, and
you could say the same of their role in the wild as well. They are
the structure that holds everything together, both physically and
aesthetically. It takes a little getting used to, planting things
that will long outlive us and that we may not see reach maturity.
(Rapidly growing wildflowers are much more satisfying in this
regard.) In fact, it is hard to really get to know individual trees
or even large shrubs because they go about their business above our
heads, out of view — mysteriously. Most of the time we can catch mere
hints of a tree"s ongoing life processes — a falling leaf, a
discarded cone, or an intricate, spotted caterpillar that has dropped
from somewhere above. So planting a tree is in some senses an act of
faith: faith in my own longevity maybe, faith in the future probably,
faith in the power, importance, and mystery of trees certainly.
I have met very few people interested in native plants who
are not also interested in the rest of life on earth. One of the
things you quickly learn about woody plants is the staggering number
of birds, small mammals, insects, and fungi, not to mention people,
that depend on them directly for their existence. Sara Stein, the
author of the Noah"s Garden series, told me recently of her
unrestrained delight upon finding pipevine swallowtail butterfly
caterpillars feeding on the Dutchman"s pipe she planted in her yard.
Truly, if you plant it, they will come. It is with the same sense of
satisfaction that I watch migrating birds feeding ravenously on the
winterberry holly I planted out back near the terrace or bees buzzing
around my sweet pepperbush. So, planting a tree, or vine or shrub is
also an act of faith in the marvelous complexity of life — a
complexity that is impossible to really comprehend but truly awesome
to behold. Go plant a tree.
What Is a Native Plant?
For the purposes of this work, "native" means plants growing in North
America prior to European settlement, and the term "woody plant"
means any species with at least a woody (or lignified) trunk or base.
The use of native plants in landscaping has become very politicized
in recent years, and this is unfortunate. Like the noted writer-
philosopher Wendell Berry, I am suspicious of movements, and do not
want to see the enjoyment and appreciation of our wonderful flora
needlessly polemicized under the auspices of a native plant movement.
Therefore, I think both the term "native" and some of the reasons for
choosing to grow these plants need further clarification.
It is natural for us humans to think of time in terms of our
own life spans, and it is certainly understandable that we see
organisms that live and die over longer intervals as having an air of
permanence. A Douglas fir that has lived 1,000 years is
incomprehensibly old to us, and to think, further, of the land itself
as having a life span is nearly impossible. In geological time, 1,000
years is roughly equivalent to 10 minutes in the life span of a
person. In this sort of relative time, it has been about two years
since the age of the dinosaurs and about two hours since the last
Wisconsin glaciers retreated north. If we could only view the earth
with some sort of super-time-lapse photography for a few minutes,
geological time would be understandable as the powerful dance of
continents, mountains, ice, and water, where forests ebb and flow
like waves on a beach and ancient trees are mere momentary bubbles in
the changing surf. With this sort of perspective it becomes clear
that what we see in the wilds at this particular moment in time is
but a split-second-long freeze frame in a much larger process, and to
draw too many conclusions about particular elements in this
composition without putting them into a geological context is a
dangerous proposition. This becomes particularly important when one
is discussing rarity and extinction or even the concept of what is a
native plant. In geological time, a plant is native somewhere only as
an airplane"s transient vapor trail is native to a particular place
in the atmosphere. Species are always in a state of flux, advancing
and receding, evolving and disappearing, their presence in any one
place only transitory. Even the land itself is constantly moving,
shifting, and recombining. How can we then say that anything is
native anywhere? It is equivalent to taking a photograph of a busy
street and from then on assuming that these people caught in mid step
have always resided on this bit of pavement and will always continue
to, unless some great catastrophe intervenes. To argue this point
would be an exercise in futility.
The important point, then, is not simply what it means to be
native, but what possible consequences displacing a particular
species from a particular place may have on the ecosystem as a whole.
This is the key argument for what ecologists call the preservation of
biodiversity. Individual species do not exist in a vacuum — the
actions of one species radiate outward like ripples on a pond,
affecting many others. For example, say the eggs of an insect that
feeds on hemlock trees are transported halfway around the globe by
some freak weather event (or with human assistance). The hemlocks in
the new region have never experienced this pest, have no defenses
against it, and begin to die out over much of their range. As the
range of the hemlock recedes, so too do the ranges of the fungi that
feed on its wood, the birds that feed on its seeds, the caterpillars
that consume its needles, and so on. The gap left in the forests by
the death of these trees allows the advance of other trees that could
not grow in the shade of the hemlock, and as this may well have been
the climax tree in the forest succession of the region, the whole
life cycle of the forest itself is altered. Should the diversity of
life be great enough, other organisms that depend on these advancing
species will move forward as well, and a few may eventually adapt to
feed on the hemlock pest itself, reversing the tide and restoring
some kind of balance. In a healthy ecosystem, such disturbances can
over time actually increase biodiversity, and the more species there
are in a particular region, the more flexible and proactive the whole
ecosystem will be. Just as it is easier to write poetry with a
vocabulary of 10,000 words as opposed to 200, so too will a large
number of species be more responsive to change and able to restore
balance after disturbance or insult. The elimination of biodiversity
dams this flow, so to speak — the water still trickles by, but the
salmon cannot swim and the bears cannot feast, the dragonfly nymphs
have less to feed on and it is hard to say whether even the quality
of the mud doesn"t change for the worse. More than any other species
on the planet, we humans have the ability to shape our environment. I
firmly believe that if we all decide to make an effort to restore
some of the local plants to our landscapes, we will in no small way
help make our own piece of the world a richer, more diverse, and by
consequence a healthier place. This is not politics; it is simple
truth.
How to Use This Book
Three years ago, when I decided to write The New England Wild Flower
Society Guide to Growing and Propagating Wildflowers of the United
States and Canada, I did so with the conviction that there was a
vital need for a comprehensive guide to the culture, personalities,
ecology, and propagation of these plants. But wildflowers are only
part of the story. What about trees, shrubs, and vines? There is
certainly more information available on native woody plants than on
their herbaceous companions, but it tends to be either regional in
focus or written in outline or table format. So I present to you here
the companion to my book on wildflowers: a comprehensive reference on
woody plants, which I hope will be useful for the novice and expert,
gardener and naturalist alike, with information presented in a style
that is approachable and easy to read but still informative and
accurate. The plants are arranged alphabetically by genus, each entry
beginning with an overview that includes anecdotes and relevant
information to serve as an introduction to the group. This is
followed by notes regarding basic cultural advice, garden uses, and,
if relevant, the plant"s importance for particular wildlife. Each
entry concludes with a list of representative species and their
particularities. General cultural information and detailed notes on
propagation are in a separate section at the end of the book.
I have sought to include woody plants from all of temperate
North America so that you can select species that are well suited to
your individual climate, light conditions, and soil. While I
encourage you to grow and appreciate the plants of your area, I also
know that we all as gardeners like to seek out the challenge of
something new and different, so whenever possible I have included
information to aid you in growing a particular plant successfully
outside its native range.
Latin Names: Family, Genus, and Species
I realize that Latin is no one"s first language, and it can be a bit
ponderous to use if you are not used to it. I have liberally used
Latin in the text, not to impress you with my erudition, but because
it really is valuable to know the Latin names and to become
comfortable using them, for two reasons. First, common names are
often wonderful and poetic, but many common names, like maple, are
generic, so it is difficult to know which plant someone is referring
to. Even more confusing are names like ironwood or sage, which get
applied to multiple genera. Second, the Latin binomial name can tell
you a great deal about a plant because it is part of a system of
classification based on a plant"s familial or evolutionary
relationships and individual characteristics. The plant kingdom has
been split into categories and subcategories on the basis of
characteristics of their vasculation, seeds, reproductive structures,
and other features, starting with the most global categories and
working down to the most specific. This classification system works
as follows:
There are two divisions in the plant kingdom. The first,
Pteridophyta, includes all the plants such as ferns and mosses, also
known as bryophytes. These are plants that reproduce without flowers
or seeds, relying instead on spores. The second division is the
Spermatophyta, or seed plants, which encompasses most of the plants
now on earth; they are more recently evolved than the Pteridophyta.
The Spermatophyta are divided next into gymnosperms and angiosperms.
Gymnosperm means "naked seed" —the ovules, or eggs, are not enclosed
in an ovary. In this group are all of the conifers and a few related
plants. Angiosperm means "covered seed," because these evolved
coverings or fruits for their ovules or seeds. This is the biggest
group of plants alive today. The angiosperms are next divided into
two classes: the monocots, plants with only one cotyledon (the first,
or embryonic, leaf), and dicots, which have two cotyledons. Among the
monocots are grasses, lilies, orchids, irises, palms, bromeliads,
sedges, and a few others, so it is clear that they are pretty
successful evolutionarily. The monocots are a personal interest of
mine. However, most of the plants we work with are dicots, a large
and highly successful group.
Both the monocots and dicots are subdivided into a series of
families. A family is a fairly manageable grouping of plants that
share certain recognizable characteristics. (All family names end
in "aceae." This is a nomenclatural convention that makes it easy to
tell a family name from a genus or species name.) The members of the
orchid family (Orchidaceae) are monocots in which the sexual parts
are united into a structure called a column; the composites
(Asteraceae), are dicots with flowers aggregated into distinct daisy-
type inflorescences. It is very helpful to know the family a certain
plant belongs too, as it gives many clues, especially regarding its
propagation and habits. Certain families, like the Ericaceae and
Rosaceae, have a disproportionate number of wonderful garden plants,
and knowing this will help you narrow your search for new
possibilities.
Families are further subdivided into genera (genus is the
singular form). A genus is a smaller grouping of plants with very
similar characteristics. Oaks are in the genus Quercus, honeysuckles
in the genus Lonicera, and firs in the genus Abies. Though beeches
and oaks are in the same family, they have been split into separate
genera because they differ anatomically and cannot interbreed.
Conveniently, plants within a genus share many of the same
characteristics, so I have used this as the organizing principle of
the book.
Genera are further divided into species. A species is a group
of genetically very similar plants or animals that are distinct from
other species in the genus. Humans are a species — Homo sapiens —
that is distinct from other (now extinct) species in the genus Homo,
such as Homo erectus. The Latin binomial (two-name) system consists
of the genus name, capitalized, and the species name, written lower
case. The genus name and species name are always italicized. The
binomial system is sort of like our system of phone numbers, with
area codes and exchanges, which allow for a great many possible
combinations. Thus Fraxinus velutina and Quercus velutina are two
very different plants with the same specific epithet. Knowing that
velutina means "velvety" tells you something about the plants too.
With plants, the separations between species are usually more blurred
than with animals. This means that you cannot assume that two plants
are of the same species if they produce fertile offspring. Though you
can tell from just looking that Ilex glabra is different from I.
opaca, a species is an artificial construct, and plants are always in
a state of flux and evolution. (Note that a repeated genus name is
often abbreviated, as in the preceding example — I. opaca rather than
Ilex opaca.)
When a plant occurs over a wide range or in geographically
isolated areas, often there are distinctive races, called subspecies
(abbreviated ssp.), which are judged to be too similar to be separate
species, but are distinct enough from each other to be recognizable.
Erigeron chrysopsidis ssp. brevifolius (meaning "short-leaved") is
slightly different from E. chrysopsidis ssp. austiniae (meaning from
Austin, Texas). More commonly, there are minor variations within a
species — like flower color, size, level of hairiness — that are not
extreme enough to be given a subspecies designation. These are noted
as varieties (abbreviated as v. or var.). Botanically speaking, a
variety represents some consistent, natural, and minor variation that
occurs within a given population of the species. In practice, the
term "variety" is often confused and applied to all sorts of things,
both horticultural and botanical. Juniperus virginiana var. glau"kame-
ee-SIP-ar-iss," people will understand, rules or no rules. With this
in mind, I have given suggested pronunciations, based on
horticultural convention, in parentheses for each genus, with the
accented syllable in capital letters.
The Genus Entries
Each genus entry has introductory text, followed by four sections:
Culture, Uses, Wildlife, and Propagation.
Culture: This section is intended to give a quick idea of how hard or
easy it is to grow the plants in the genus and specific requirements
(such as transplanting times and soil type), to help you decide if it
is appropriate for your conditions. If individual species are quite
different from the rest of the genus, I try to single them out here
or in the species descriptions. I have avoided pointing out every
possible pest or disease that might afflict the genus, mentioning
only those serious enough to threaten the health of well-sited,
otherwise vigorous individuals. See the chapter on propagation (page
261) for more comprehensive information.
Uses: Here I briefly list some of the possible situations and uses
the particular genus is suited for (for example, shade tree, hedge,
groundcover, soil stabilization), again to give you some ideas, but
not to limit your own imagination. See also "Native Trees, Shrubs,
and Vines for Various Sites and Uses" on pages 303–311.
Wildlife: One of the strongest reasons for using locally native
plants is their inestimable value to myriad nonhuman organisms that
have evolved with, and come to depend on, these plants for food and
shelter. There is not a great deal of information available about
plants" relationships with specific beetles, moths, fungi, or
bacteria, but there is more on their benefits to birds, mammals, and
butterflies, and so I have concentrated on the latter groups.
Butterflies in particular are fascinating not only because they are
beautiful and well studied and documented, as compared to moths or
fungi, but also because their larvae often depend on just a few
species or genera of native plants for food. Planting a pipevine and
watching the pipevine swallowtails show up in your yard where before
there were none fosters one of the most direct and powerful
connections between your own action — planting this native species
and not a nonnative vine — and the benefit to biodiversity of
allowing a species to reproduce in an area where it formerly could
not. I like to think of butterflies as the poster children for hands-
on efforts to increase the biodiversity in your own backyard, though
they represent just the tip of the iceberg as far as the total number
of native species that might benefit in some way when you plant a
pipe-vine, American beech, or California sycamore.
Propagation: I realize that not everyone is interested in
propagation — but you should be, you really should be! Accordingly,
I have organized the propagation information in a table that begins
on page 277. Under the genus description in the main body of the
text, I have briefly indicated the general ease or difficulty of
propagating from seed or cuttings for the genus as a whole. The four
categories are easy (can be propagated by a beginner with little
specialized equipment), moderately easy (some experience required,
but again, requiring little specialized equipment), moderately
difficult (requires experience, specialized equipment, or is slow to
propagate), and difficult (challenging even for an expert with
specialized equipment).
The Species Entries
Each species entry provides information in the following categories:
Zones, Soil, Native to, Size, and Color. This is followed by a
general description of the species.
Zones: I have based winter-hardiness on the revised USDA Plant
Hardiness Zone Map (pages 336–337). The map breaks down North America
into a series of zones, from 1 to 10, experiencing gradually colder
average minimum winter low temperatures. The coldest zone is Zone 1;
the warmest, Zone 10. A hardiness zone indicates the areas where the
average minimum winter temperatures in a given year fall between a
certain range. For example, Garden in the Woods, in Framingham,
Massachusetts, lies in USDA Zone 6, where average winter minimums
are –10 to 0° F, though in many years we have lows well above zero
and once in a great while there are years where they fall below –10°
F. For each of the featured species, I have included a hardiness
range that I have arrived at on the basis of personal experience,
references such as Dirr"s Manual of Woody Landscape Plants, and the
natural range of the plant. I include an upper and lower zone limit
for each plant, the lower limit (smaller number) being the coldest
zone in which it will grow and the upper being the warmest limit it
can tolerate. This warmer limit needs further explanation. When I
state a plant"s range as Zones 4–7, I mean to indicate not only its
cold tolerance, but also its unsuitability for gardeners in most of
Zones 8–10, where summers are too long and warm for the plant to
thrive. (An exception is the Pacific coast, which benefits from a
cool maritime climate where both winters and summers are mild.) In
some cases, I have included a zone in parentheses — for example,
Zones (4)5–7 — to indicate that a particular species may be more cold
(or heat) tolerant if sited carefully.
I have found hardiness ratings to be a useful general guide
when selecting plants to try, but please keep this information in
perspective. There is much more to determining a plant"s hardiness in
a particular situation than simply its tolerance of cold. Other
climatic factors include the amount of annual solar radiation, the
altitude, the average relative humidity, patterns and amounts of
rainfall and snowfall, reliability of snow cover, average summer high
and low temperatures, and length and severity of extreme hot and cold
temperatures. Prolonged temperatures below 20° F or above 90° F are
much harder for many plants to endure than a brief chill or heat
wave. Furthermore, factors like the windiness of the site, the freeze-
and-thaw patterns and depth of soil frost, and seasonal day length at
a particular latitude all play a part in determining a plant"s
hardiness. So even though Sable Island, Nova Scotia; Cape Cod,
Massachusetts; Raleigh, North Carolina; Albuquerque, New Mexico; and
Juneau, Alaska, are all within USDA Zone 7, they have vastly
different climates and it is rare to find a plant that will thrive in
all of them. Plant hardiness is a subject on which I could easily
write a book, but rather than developing more sophisticated hardiness
ratings, I think it is simply far less complicated to grow the plants
native to your area whenever possible and, further, to seek out
genotypes that originate nearby if you can. An Acer rubrum from
Florida will likely grow better in Georgia than one originating in
Maine. If you want to grow plants from farther afield, look first for
species with ranges that are close to yours in latitude or longitude.
A plant from southern New Mexico will have a better chance in Georgia
than Wisconsin, and a gardener in Alberta will be more likely to
overwinter plants from Saskatchewan than New Brunswick. Pay close
attention to soil recommendations and remember that a healthy,
established plant has the best chance of survival.
After the hardiness zone in the species entry is the
preferred sun exposure. "Sun" means full sun, or at least six hours
of direct sun daily in midsummer; essarily mean that the plant could
not thrive in a garden in Nova Scotia or New Mexico or, conversely,
that it occurs within every state within the range.
I compiled habitat and range information from a number of the
sources listed in the bibliography, especially Gleason and Cronquist,
Manual of the Vascular Plants of the Northeastern United States and
Adjacent Canada; Hitchcock and Cronquist, Flora of the Pacific
Northwest; Radford, Ahles, and Bell, Manual of the Vascular Flora of
the Carolinas; Morin et al., Flora of North America, vols. 1 and 2;
Cronquist et al., Intermountain Flora; Steyermark, Flora of Missouri;
Martin and Hutchins, A Flora of New Mexico; Munz, A California Flora;
Hortus Third; and the Great Plains Flora Association, Flora of the
Great Plains.
Size: The height given is the average height under cultivation. A
wide height range — say 20–60 feet — usually indicates that the plant
height varies depending on conditions. Some species (Abies grandis,
for example) can attain a great height in the wild; in such cases I
include that height in parentheses just as a matter of interest, not
as a realistic reflection of what to expect in cultivation. The
figure given for width is the plant"s expected width within 5 to 25
years in the garden, depending on the plant"s rate of growth and
whether it is a long-lived tree or shrub. This figure should give an
idea of necessary spacing. Again, I have occasionally included a
third number in parentheses to indicate potential size of very large
wild individuals. Most vines vary greatly in both height and width,
depending on how they are supported.
Color: I have tried to be as detailed as possible about flower color.
Many entries list a range, say from violet to purple or white, that
you might find within the species as a whole. For conifers, whose
flowers are enclosed in cones, not petals, I give the cone color at
the time of flowering. Similarly, for plants that produce catkins
(birches, for example), I give the color of the catkins. As for
flowering season, I list the time of year rather than specific
months, since the weather month by month varies greatly from region
to region. If your spring lasts from early March until late May
(aren"t you lucky!) then a flowering time of late spring would be mid
to late May.
The New England Wild Flower Society originated in response to
unrestrained plant collecting that was devastating populations of
certain vulnerable ferns, club mosses, and woodland wildflowers.
Although collection of plants by individuals can damage local
populations, the commercial collection of wild plants for the nursery
trade poses much more of a threat. Short of direct monitoring, there
is never any assurance that wild collection is not depleting local
populations beyond their capacity to regenerate. The New England Wild
Flower Society strongly recommends purchasing propagated plants and
strongly recommends against purchasing any wild-collected plants.
Just as a rise in the demand for fish has nearly exterminated
all the commercial fish species of the North Atlantic, so too the
increasing popularity of native plant gardening threatens the health
and stability of wild populations everywhere. The vast majority of
plants sold today are nursery-propagated (grown from seed or
cuttings/divisions of nursery stock), but the slow-growing woodland
and bulbous species are especially vulnerable and are still harvested
in unconscionably high numbers. These include many of the lilies and
lily relatives such as trilliums, mariposa lilies, and trout lilies,
bloodroot, bluebells, hepaticas, lady-slippers, and gingers, to name
a few. Some shrubs, like rosebay rhododendron, are routinely cut
back, dug, and sold as "cut-offs" for a fraction of the price charged
for nursery-raised plants.
Forestry practices that put maximum profit above the health
and persistence of ecosystems are equally disturbing. The mindless
cutting of our last stands of old-growth timber and the replacement
of species-diverse wild forests with genetically engineered,
industrial forest monocultures makes about as much sense to me as
cutting off your foot when you can"t get your boots untied. The only
way to stop this depredation is to eliminate the demand. When buying
woodland plants, balled and burlaped shrubs or trees, or even lumber,
ask your supplier about their source. If the supplier is unsure or if
the price seems too good to be true, look somewhere else. Be
skeptical of supposedly "rescued" plants (plants dug from areas about
to be developed or paved over). I know from personal experience of
unscrupulous collectors who market supposedly rescued plants actually
dug from safe, healthy populations. While I hate to see plants being
destroyed under a bulldozer, the term "rescued plants" is too open to
interpretation and abuse at this point to be anything more than a
loophole for disreputable collectors.
Copyright © 2002 by The New England Wild Flower Society. Reprinted by
permission of Houghton Mifflin Company.
Library of Congress subject headings for this publication: Ornamental woody plants United States, Ornamental woody plants Canada, Native plants for cultivation United States, Native plants for cultivation Canada, Woody plants Propagation United States, Woody plants Propagation Canada