D is for...

Deciduous
I did think about doing this for 'F' for Frost but then I had a more obvious idea for F - look out for that one!
The leaves are from a cobnut tree which is covered in beautiful catkins at the moment. We planted the tree about 8 years ago and for the last 2 years we've enjoyed a bumper harvest of cobnuts. We often find the shells in the garden shed left behind by over-wintering mice - glad to see that some have survived hunting by our black tom cat!