Most of my dahlias are safely out of the ground and tucked up in pots in their shed for the winter. Those that I’ve left in the ground have been given a deep covering of cow manure to protect them from the frost. All, that is, except for the tree dahlias, which are impervious to the early frosts and will carry on flowering until well into the new year. The first few weeks of winter this year has been pretty horrid, with a series of sharp frosts and some hefty storms, but that hasn’t deterred the tree dahlias, which have continued to thrive. The best performer has been the D. Excelsa, pictured here on Christmas Day. This particular plant is one of half a dozen cuttings taken in May this year. All are strong and healthy, and will outperform the more popular D. Imperialis, which, although much taller, has not got enough strength to flower outdoors this year. The last time it achieved that feat in my garden was after the long hot summer in 2006, when it came into flower on December 6th.