Home & Garden Columns

Green Neighbors: Silk Oaks Are Itchy, But Oh Those Blooms!

By Ron Sullivan
Tuesday May 08, 2007

There aren’t lots of them around, but many are in bloom now so it’s a bit easier to spot them: silk oak, Grevillea robusta. Their leaves have a distinctive profile, a bit like an exaggerated oak-leaf shape, verging on the fernish; I suppose that might account for the name, but the Aussies have a habit of calling any old thing some kind of “oak”—casaurina is “she-oak” for example, and that genus has foliage that looks like pine needles.  

Look for a tree with gray bark, floppy ferny leaves about as long as your hand, and orange flowers, probably up high in the tree. If you have the flower in hand, you’ll see it’s actually scarlet and yellow, an odd long brush of curled flowerets like a row of inquisitive cartoon ants.  

The Grevillea genus stems from a clan with a habit of producing weird flowers. It’s a protea, if you don’t mind—one of that family that includes those strange silvery South African plants with big blossoms like the offspring of an artichoke and a cactus. I find myself groping for similes to describe this stuff, because it’s practically extraplanetary to look at.  

The family’s actually a respectable old Terran one, though from when the Earth wasn’t Earth as we know it, quite. It’s one of those Gondwanaland groups, like araucarias—monkey puzzle and bunya-bunya trees and such—and the particular distribution of those groups over the world is one of those mind-boggling signatures of continental drift.  

No, really. Imagine discovering that the reason you were born where you were born was that your ancestors had traveled there without taking a step, but by riding the ground they stood on while it surfed the Earth’s mantle for eons. The idea that life forms are older than the ground they stand on or the acre next door messes with the usual pictures of planetary history we tend to have in our heads. You can meet similar temporal disjunctions on the east slope of the Sierra, looking from recent volcanic-glass mountains and underwater instant-hot-tub vents toward the ancient bristlecone pines in the White Mountains just to the south.  

Or, what the heck, go to the Big Island of Hawai’i where islands of vegetation stand among barren lava flows. Take Joe and me along, please. We can all look for silk oaks there; the species is in use for landscaping, shade (as in India, Sri Lanka, and Brazil, for tea and/or coffee plantations), and sometimes timber. It’s getting a bit invasive there, though; uh-oh. 

Other grevilleas are more shrubs than trees. You’ll find some of them here and there around us in garden settings; they tend to be drought- and heat-tolerant, shearable for hedges, and decent looking.  

I myself dislike those shrubs strongly, but it’s a personal grudge. When I was a practicing pro gardener with a few accounts over the hills in Contra Costa County, those were about the meanest, prickliest, itchiest buggers I had to mess with, and lots of them were on slopes where I could barely keep on my feet without grabbing something. Not much to grab but a fanged bush. Ow.  

No, gloves didn’t help much. Somehow the thin needly leaves found the seams and that gap at the cuff. As I said: mean.  

If you get close to one of those, though, look—carefully—at the flowers: maybe stranger even than silk oaks’. Art deco snails with periscopes.  

grows fast—not an unmixed blessing—and sheds lots of leaves and twigs; it’s the sort of pet a large drooly dog might be. Ideally it lives in a spot where the dropped leaves can be left to compost where they land, as mulch. It flowers more reliably in warmer places like Hawai’i and south Florida.  

It also has the distinctive root system that typify its family: proteoid lateral roots, short, dense, and good at using scarce nutrients in poor soils by extracting those nutrients from their mineral matrix.  

So if you have a warm rocky spot at the back of a sizeable garden, this might be the tree for you. Frankly, you and your garden’s animal commensals would be better off with a native, but I couldn’t blame anyone who got a good look at a silk oak’s flowers for falling in love with them. 



Photograph by Ron Sullivan: At the top of this silk oak in downtown Berkeley, you can  

see its flowers. If you're preternaturally sighted, you can see a lesser goldfinch too. 



Ron Sullivan is a former professional gardener and arborist. Her “Green Neighbors” column appears every other Tuesday in the Berkeley Daily Planet, alternating with Joe Eaton’s “Wild Neighbors” column. Her  

“Garden Variety” column appears every Friday in the Daily Planet’s  

East Bay Home & Real Estate section.