i have what i call a snowball plant i think its verburnum opulus sterile. it has white snowballs on it flowering now.its been there about 10 years. however this year i have no bobbles on the lower half but big ones all over the top half. i prune it into shape every year when the flowers finish. can anyone tell me why i have no lower bobbles this year? its usualy evenly covered.

I've checked my RHS pruning book and it says that you should not really be pruning a mature viburnum, except to remove dead, damaged or diseased growth. 

It also says that for this type of shrub that they, "do not regularly produce vigorous replacement growths from the base or lower branches of the plant.  Their extension growth is produced on the perimeter of a permanent framework of older branches.  The growth habit, therefore, may be likened to the crown of an oak tree without its trunk."  So I guess what you are seeing is actually somewhat natural for a mature specimen.

My former gardeners used to prune everything to shape - but just the "outside" of shrubs - I swear they have killed at least three mature shrubs doing so.  Usually there is a year where they look horrible and sad ... and then the next year they are all but gone.   And I am keeping my fingers crossed that my hydrangea which they pruned so hard the year before last that it did not flower last summer will flower this year.  

So, IMO, I would replace the shrub.  (And I've replaced my gardeners, with ME.)

thanks for the info. i dont excactly prune but mostly cut off the dead flower heads and hub does the top which i cant reach but the non flowery bit was hardly cut at all except for flower heads. it could just be that it is mature then as the bobbles are certainly bigger than before but i coudnt replace it! its been my baby for at least 10 years! its the only thing that has grown in my garden as i have non green fingers!