Posted: 26/07/2012 at 16:00
Yes, Viburnums are sometime grafted, but not onto Silver birch. Viburnums are grafted onto Viburnums, often V tinus. Birch is in a genus of its own, Betulaceae and Viburnums are in Caprifoliaceae, along with things like Honeysuckles, Abelia and Diervilla. They are just not compatible in any way. The Silver birch which grew from your can only have been a seedling.