Looked on the web and found this one which I hope is the one you mean. It's by Mary Webb of Shropshire.
'The birds will sing'
The birds will sing when I am gone
To stranger-folk with stranger-ways.
Without a break they'll whistle on
In close and flowery orchard deeps,
Where once I loved them, nights and days,
And never reck of one that weeps.
The bud that slept within the bark
When I was there, will break her bars--
A small green flame from out the dark--
And round into a world, and spread
Beneath the silver dews and stars,
Nor miss my bent, attentive head.