When fungi start to take over from vascular plants for a few weeks. A field meeting with the West Weald Fungi Group to Winkworth Arboretum (where I first went out with the group two years ago) was relatively quiet fungi-wise but there's always something of interest to see.
Chestnut Bolete - Gyroporous castaneus
Fluted Bird's-nest - Cyanthus striatus
And the trees were just starting to turn as well.