June 2008 In the Garden
Saturday, May 31st, 2008
Gardening is a full contact sport – we all know that. We know not to expect glamorous fingernails. The ground-in dirt along our fingers from dead heading and weeding and squashing aphids – we don’t expect this to come off. We hold no shoes as sacred because it’s always when we walk past the garden in our dress shoes that we see the dead head or the weed and we tromp through the dirt and stones anyway. We expect scrapes, bruises, bug bites, aches and festering thorn tips in the pads of our thumbs. And most of the time we love our gardens and our work in them anyway. But here’s something I don’t love. Poison oak. I had my first round of the year in January. May brought my next round. The swollen, weeping, red rash spread across the left side of my face, my neck and both shoulders. I must have walked right through it. Photo above: Poison oak in bloom.
I can generally identify poison oak. But I clearly have more to learn. When a friend asked me what poison oak was and I responded with: some evil variety of oak. Another friend, Ray Barnett, corrected me by saying that it was not an oak at all.
Here’s where the more to learn comes in. Poison oak’s botanical name is Toxicodendrun diversilobum. Although it used to be considered a member of the Rhus genus, Toxicodendron is now its own genus and consists of woody trees, shrubs and vines in the Anacardiaceae or Sumac Family and that produce the skin-irritating oil urushiol, which causes the rash – also called contact dermatitis. Poison ivy and poison sumac are also members of this genus. Photo above: California Buckeye (Aesculus californica) in bloom.
One of the tricky things about poison oak, ivy and sumac is how variable they are. The leaves may have smooth, toothed or lobed edges, and all three types of leaf edge may be present in a single plant. The plants grow as vines, shrubs, or small trees. While stems of Poison ivy and poison oaks usually have three leaflets, sometimes there are five, even seven. The common name poison oak comes from the leaves’ resemblance to the leaves of the white oak (Quercus alba). Photo above: a blue oak in early summer. All parts of the plant contain the irritating oil – the leaves, dormant stems, even the roots and the dried leaves. Poison oak
is deciduous in the Northstate and one tell-tale identifier is the plant’s rusty-red new growth in early spring. Poison oak grows throughout the Northstate’s foothills and valleys, and while some people are less susceptible, most people will develop the rash if they come in direct contact with the oil. Some say that you can develop immunity, other’s say that you can lose resistance or immunity with repeated exposure. The native people of the Northstate are thought to have eaten the berries of the plant in order to build immunity. Photo above: June salad greens.
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