The alders in the Betulaceae are wonderful at this time of year as the pagoda structure of branches are festooned with catkins, as though responding to some imperceptible signal of srping.
Alnus incana 'Aurea' is one of the earliest to produce catkins, the bright pink new growth ending in orange-pink catkins that quickly elongate and disintegrate.
Moving east along the south walk, on your right you will come across three more mature alders all covered in distinctly different catkins. The first, Alnus hirsuta, is a haze of dusky pink and yellow catkins suspended from fine networks of branches. Then comes the lime green and yellow crumbling catkins of the Alnus subcordata. Finally there's the pinky blue catkins still tightly closed and iced in frost of Alnus glutinosa, the new male catkins and mature cones hanging side by side.