I imagine that those brought up to think that a poem must always mean something beyond itself may find this little piece, together with why I find it so satisfying, somewhat puzzling. ‘Yes, but what do the nettles represent?’, they may ask. Nothing, so far as I know: they are just nettles in their own right, a humble and easily overlooked part of the creation, but this time they have been seen, and the poetry is in the seeing. It is as Thomas himself observed of his hero Richard Jefferies: ‘To see… as clearly as he saw the sun-painted yellowhammer in Stewart’s Mash is an office of the imagination’. And when it results in observation as affectionately meticulous as that in the last three lines of this poem, it is no mean office either.
Tall Nettles
Tall nettles cover up, as they have done
These many springs, the rusty harrow, the plough
Long worn out, and the roller made of stone:
Only the elm butt tops the nettles now.
This corner of the farmyard I like most:
As well as any bloom upon a flower
I like the dust on the nettles, never lost
Except to prove the sweetness of a shower.
Edward Thomas
David Sutton 
“the poetry is in the seeing.” – hard to state the obvious poetically – so often we veer into the high-falutin and lose the beauty of what Thomas gave us here
I suppose you could say, it’s not the nettles so such as the avoidance of the dead weight of the last century, that he writes about and that they capture of him. To find somewhere off the main road, somewhere forgotten, somewhere allowing solace, after the bruising political, imperialist, socially broken and culturally autocratic Victorian death throes all around him at that time.
Bit of a mouthful, but I think you get the gist.
Also, is there here an echo from his Welsh heritage, of those old Welsh poems of Taliesin and his contemporaries Llywarch Hen, about the ruined great houses? The settings are similar.
Not Taliesin, I think, who is more battles and praise poems and mythological stuff, but the Heledd cycle of Llywarch Hen possibly and there is also the Old English poem ‘The Ruin’ that he may have known. But that sort of connection would work better with a poem like Housman’s: ‘It peoples towns, and towers/About the courts of Kings/And touch it and it stings’. The spirit of Thomas’s poem is not at all like that, nothing to do with ruin and desolation – he likes nettles!
I remember having nettle tea in a shop in Bangor, North Wales. So, nettles are indeed liked.
My son down in Pembrokeshire, who is much into food for free – I blame Richard Mabey – cooks and eats the things. I remember my two year old grandson patiently explaining to a hesitant granddad that when cooked ‘they don’t ’ting you’.