In recent Plant Man columns, we’ve looked at plants that you might
want to avoid because they can become invasive and take over your
landscape to the detriment of other plants.

But are there plants that can actually kill? Perhaps alter the course
of history? Unlikely as that might seem, a recent book takes a
fascinating, if gruesome, look at what the author calls wicked plants.
I’ll give a brief review of that book later in this column.

But, thank goodness, most plants are far from evil! Even in a
relatively small space, carefully selected plants can increase privacy
without giving you a sense of claustrophobia. The trick is layering
and including columnar-growing trees that fit the scale of your
landscape, as I explain to this reader:

QUESTION: “When I bought my house, it had what I believe are oak trees
in one corner of the smallish back yard (total yard size is 0.3 acres,
less than half that in the back yard). They have grown very tall, yet
thin. I don’t really like them. I’m looking to do the other corner of
my yard with a faster growing tree that I can cluster in the corner –
like Crape Myrtles (I heard the Dynamite are great). My fence is the
standard 4 feet, natural wood.

My questions include:
What types of trees will be a good fit for the corner? And how far
apart should I plant them? I’m looking for a pretty thick coverage.
I heard layering is a good practice. What are some nice medium sized
trees or shrubs to combine with the bigger trees?
What can I do to improve the existing oak trees? Can I prune to make
them thicker, broader?
I also have a river birch in my front yard that we planted about two
years ago. It doesn’t seem to be growing very fast. Anything I can do
to help it out?” – Thomas G. Burgess
ANSWER: The oak trees you are describing sound old and scrubby. If
that is the case, then there really isn’t anything you can do to
thicken them up. Since you have a small area to work with, you should
consider trees that are more columnar (narrow) growing such as emerald
green arborvitaes and other smaller sized shrubs and trees.
The Dynamite crape myrtle is also a smaller growing tree and would
work within that sizing. However, if it would receive any shading from
the fence, house or oak trees, it will not bloom properly. Crape
myrtles need full sun for consistent blooming.

Layering is an attractive way to build privacy from the outside.
Layering can be achieved by the strategic placing of taller growing
plants such as emerald greens at the back ( they can be spaced
approximately 5 to 6 feet apart), coming forward with contrasting
colored shrubs such as barberry Sunjoy Gold Pillar, weigela Wine and
Roses, Beauty Bush Dream Catcher, or taller growing ornamental
grasses. Using colorful perennials on the most inside areas add one
last punch of color.

Birches aren’t all that fast growing especially in clay soil. It may
take it several years, but it will grow.

And now to those “naughty” plants…

If it was a tabloid-style TV show, it might be called “When Good
Plants Go Bad.” However, the new book by Amy Stewart is titled “Wicked
Plants” and is a compendium of plants that can kill, injure, torment
and cause all kinds of trouble to humans, animals and other plants.

On one level, “Wicked Plants” is simply an entertaining read with
plenty of botanical trivia and gruesome stories of plants behaving
badly, as you might guess from the book’s sub-title: “The Weed that
Killed Lincoln's Mother & Other Botanical Atrocities.”

But there is more than just grisly fun to be found here. On a more
practical level, “Wicked Plants” can be a warning about what NOT to
plant, or at least what will happen if you do.

As author Amy Stewart says, “These are plants you do not want to meet
in a dark alley.”

The Plant Man is here to help. Send your questions about trees, shrubs
and landscaping to and for resources and
additional information, including archived columns, visit www.landsteward.org