I deadheaded the hogweed that grows in one of the borders in the back garden today. I felt slightly regretful as I did, because the large, flat flower heads have a fine, architectural silhouette as they turn to seed, and add height without casting much shade. The average height of common hogweed according to Wikipedia is between 50 and 120 centimetres, with a maximum of two metres. Mine must have enjoyed life in a flower bed that was dosed last winter with spent mushroom compost and blood, fish and bone, since it shot up towards not far off the two metre mark. But the architectural heads don't hold on to their seeds for long before scattering them generously, and the large, flat brown seeds germinate readily, each turning into a little parsnip rooted miniature hogweed that requires winkling out with the point of a trowel. I spent a great hunk of time last winter teasing tiny hogweeds out of the beds in the back garden, and don't want it to become an annual ritual.
On my visit to Corpusty Mill I saw giant hogweed in the flesh, with the garden owner present to vouch that that was indeed what it was. He had two stands of it, and was slightly defensive when we asked if it was really giant hogweed, stressing that the seeds could not escape into the wider countryside from the places in his garden where he had it, and yes, he did let it set some seed in order to keep it going in the garden. That might be a wise precaution if you want to grow it, since fewer outlets sell it now than formerly. The plant centre stocked it the first couple of years I worked there, but dropped it at much the same time as they stopped selling the species of Rhus with particularly noxious sap.
The sap of giant hogweed can produce very nasty blisters indeed by the particularly unpleasant mechanism of making the skin sensitive to light, so that even after the victim's initial injuries have healed they have to protect the affected area from further sun exposure. They are likely to be scarred, and in the worst case blinded if the sap gets in their eyes. It is really not a nice plant. And yet it is very handsome, quite apart from the illicit thrill of harbouring something so dangerous. I wouldn't grow it myself, not least because I wouldn't enjoy the feeling that I was taking my sight in my hands each year when I deadheaded it, and while I could tell human visitors not to touch it I would worry about the cats.
Now I've seen the common and giant hogweeds in full flower I wouldn't confuse the two. Giant hogweed is not just taller, it is more giant in all its parts. The leaves are bigger and shinier and more divided than those of poor old cow mumble. The flower heads are enormous and multi branched, each individual umbel a gigantic saucer with saucer upon saucer heaped up to make the whole. The stem is a brighter green. I have witnessed well grown examples of the common hogweed produce the odd nervous squeak from people worried they might have the giant one on their hands, but really the two are quite different.
Tomorrow I might cut down the angelica stems in the rose bed. Strange that when giant hogweed is so toxic, and even common hogweed sap is to be avoided, angelica stems can be candied and put on cakes (even if they have gone completely out of fashion). The angelica seed heads are big orbs atop stems fully six feet tall, and again they are fine architectural features, but weeding out angelica seedlings is about as tedious as dealing with baby hogweeds. And I must definitely hoik the flowered parsley stems out of the dahlia bed before they can leave me with a thousand million little parsley plants all over the gravel outside the blue shed.
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