This is fasciation and to be honest I don't know why it happens!

Thanks MG. I have heard of that, but it is usually with flower stems isn't it.

Yes it is - we see it with some of our bulbs in pots... will happen one year - the next they are fine!

Take a look at http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=525 on the RHS website. Oh and don't try to put a plant on the show bench with fasciation!

I wouldnt dream of doing that. Thanks will look that up.