The Promise and Perils of Growing Poisonous Plants

Caladiums contain calcium oxalate crystals, causing severe mouth irritation to any creature that might take a nibble.

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Would you knowingly plant a poisonous plant in your garden?  Many of us would respond with an immediate and emphatic, ‘No!’ especially if they also tend small children and pets.  And for good reason.  No one wants to put their children, pets, or livestock in harm’s way.

And yet many of us are already growing highly poisonous plants unawares.  They are a part of our landscape, or they crop up as ‘weeds.’  Many are otherwise highly valued native plants.  And we never experience a problem because they aren’t the sort of thing that children or pets would choose for a snack.

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All parts of the Red Buckeye tree, Aesculus pavia, are poisonous. Mine has never been bothered by deer, though pollinators love it.

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The Virginia Cooperative Extension Service published a new digital booklet, The Socrates Project, as a cooperative venture between Virginia Master Naturalists and the Blue Ridge Poison Center at University of Virginia Health, and the University of Virginia School of Medicine’s Division of Medical Toxicology – Department of Emergency Medicine. The document details the toxic nature of nearly 50 plants native or naturalized in Virginia.  The Second edition of this free publication was released last month.  Its name is a reference to Socrates’s death from drinking Hemlock.  Hemlock grows wild in Virginia.

 

The booklet clearly shows whether a plant is only poisonous If ingested, or whether it is also poisonous to the touch.  It describes the common symptoms of the poisoning, wildlife benefits of the plant, where it is commonly found, and traditional uses by our first nations.  It is a fascinating booklet, expertly produced with good photography, and I highly recommend it.  Although it is written for Virginia, many of the plants grow over a much wider range.

With firm acknowledgement that poisonous plants can be dangerous if misused, I still choose to plant many poisonous plants in our garden because they are the most likely to survive the wild grazers, like rabbits and deer, who frequent our garden.  If fact if a fellow gardener were to ask me for advice on what to plant, if they had the same trouble with grazers, the plants I recommended would likely also be poisonous ones.

Even so, these ‘poisonous’ plants, like the beautiful Virginia Creeper vine and Rhododendron shrubs may still sometimes suffer grazing, especially on tender new growth.  In talking with other gardeners, a lot depends on the wildlife that frequent one’s own neighborhood, and how desperately hungry they get at certain times of year as to what they may or may not eat.

There are certain plants that a sane gardener simply would never intentionally plant.  Poison Ivy, Hemlock and Hogweed come to mind.  They aren’t that attractive, there are better alternatives for the niche they might fill, and they are highly dangerous. 

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Mistletoe berries are poisonous to humans, but they provide vital winter food to many birds and other small animals.

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There are other plants that while highly lethal if ingested, are beautiful and have their uses.  Oleanders make wonderful blooming street shrubs in coastal Virginia cities.  Castor bean plants are dramatic and beautiful at the back of a bed, but their species name say it all:  Ricinus.  The Castor bean, and its oil, have many traditional uses.  But a single seed can be lethal, if eaten.  A number of ‘poisonous’ plants have long been used medicinally, when properly prepared and carefully dosed, to sustain life.  Digitalis, our beautiful Foxglove flower, comes to mind.

This is a subject worthy of study by any serious gardener.  It helps in choosing plants that will persist without becoming lunch for a hungry rabbit or deer.  But it also helps us to manage our gardens so that no harm comes to ourselves, our pets, and visiting children. 

Many common and popular plants might seem attractive, or might look edible, when in fact they aren’t.  Before foraging for wild food, positive identification and deep knowledge of edible plants could save a life.  The Socrates Project points out plants that may appear edible, or be confused with other edible plants, when in fact they are poisonous.  Some, like the potato, might have edible tubers but poisonous leaves.

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Most of a Passiflora vine is poisonous. Though ripe fruit may be edible, never eat the skin or seeds.

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Most experienced gardeners learn to wear gloves along the way.  They protect our hands from little nicks and scrapes, thorns and prickles.  But they also protect us from urushiol, the active ingredient in poison oak, poison ivy, poison sumac and some other plants. One never knows, when reaching into a mass of plants to pull a weed or snip a stem, whether a bit of poison ivy might be hiding in the mix.

The sap of hogweed and a few other plants is toxic enough to cause blisters on contact.  Gloves also offer a layer of protection when handling other less toxic plants, but whose poisonous compounds can be absorbed through the skin, like Hellebores.  These toxins have a greater effect if the skin is already broken.

As with so much in life and in the garden, we proceed with common sense and as much knowledge as we can gather.    With all of this in mind, allow me to share some of my favorite poisonous plants, and how I use them:

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Narcissus with Vinca minor and Hellebores, all poisonous, protect nearby shrubs from vole damage.

Narcissus

A daffodil by any other name is still a welcome sign in spring.  Not only do they lift our spirits after a long winter and fill our empty planting spaces early in the season, but their flowers and bulbs don’t fall prey to hungry critters.  Plant tulips and watch the squirrels dig them up for a snack.  Plant daffodils, and watch them increase year to year, because no animal will eat them.  Even better, their roots are also poisonous, stopping voles in their underground travels.  I use daffodils to disrupt vole pathways and to protect the roots of newly planted trees and shrubs with a ‘curtain’ of poisonous Narcissus roots.

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Hellebores

Evergreen, winter blooming in intensely poisonous.  Hellebores will be ignored by grazers, but their roots will also protect the roots of other nearby plants and will disrupt the progress of moles and voles.  Hellebores bloom and provide forage for pollinators when little else is available and may be cut for the vase.

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Columbine

Columbine flowers bloom in mid-spring over a month or more and their leaves often persist through our winters.  They self-seed, spreading themselves around, and have charming flowers in a variety of bright colors.  I love them planted around our Iris.  I love everything about Columbine and they are very easy to grow in a variety of soils and light levels.

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Vinca minor surrounds this pot of Viola and fern.

Vinca minor

Vinca came with the property.  I didn’t plant it and, and it is a European plant that has escaped cultivation to naturalize in our area.  It is considered invasive and is very hard to eradicate once it roots into place.  That said, it makes a dense, durable ground cover to protect the soil, remains green year round, and covers itself in tiny pastel flowers each spring.  And, it is poisonous, containing many different alkaloids.  Deer and rabbits leave it alone, and so will I. 

Ivy, Hedera species, fits this profile, too.  Deer occasionally nibble a leaf, but the vine endures.

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Any Aroid

Aroids, of which there are hundreds of species, all contain calcium oxalate crystals in their tissue, which causes burning, stinging and swelling of the mouth and gastric irritation when eaten.  While irritating, these generally aren’t lethal and there is no danger in handling any part of the plant.  Aroids are particularly ornamental and include:

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Caladiums

 

Colocasia ‘Tea Cups’ towers over this bed at the Williamsburg Botanical Garden

Colocasia

 

 

Alocasia

 

Italian Arum bloom in May and then their leaves die back as the weather warms in early June.

Italian Arum

 

Zantedeschia

 

Native Jack in the Pulpit leaves grow among ferns at the Williamsburg Botanical Garden

Jack in the Pulpit

 

Tall Voodoo Lily leaves tower over a bed of ferns

Voodoo Lily, Sauromatum venosum

 

Mayapples, Podophyllum species

Ephemeral, appearing in mid-spring and gone by mid-summer, Mayapples slowly spread in dappled shade.  They form a low ground cover of interesting leaves but their flower and fruit grow inconspicuously under the leaf.  They grow through a carpet of ground cover vines in our garden, below a hedge of Azaleas.

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Mountain Laurel, Kalmia latifolia is so poisonous that honey made from its nectar shouldn’t be eaten.

 

Mountain Laurel, Kalmia latifolia

An evergreen shrub, Mountain Laurel blooms in late spring, usually around Mother’s Day, in dappled shade under established trees.  It can grow in full sun and often colonizes steeply sloping land on riverbanks and in the mountains.  Its beautifully twisted branches have attractive uses in floral arrangements.  Honey made by bees foraging on Mountain Laurel may also be toxic.

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Rhododendron

Although the Socrates Project lists Rhododendrons, including native Azaleas as toxic, I frequently find ours grazed by deer.  These shrubs are beautiful and useful but may still need protection, especially when young.  Honey made from their nectar may be toxic.

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This is a short list of favorites, and you might have your own favorite poisonous plants to add.   I hope it both gives hope to those who endure frequent grazing in their gardens, and also helps reassure gardeners that just because a plant is poisonous, that it will cause them or their family harm.  Most all of us already have some poisonous plants. 

The art of growing poisonous plants is in selecting them wisely, managing them carefully, and learning enough to feel confident in growing them.

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