[SpudtheBinx]

I have a patch behind my shed that is useless really so I was thinking of growing some epimedium on there to smother any weeds after I have cleared it. This is I have no idea how fast it will grow and hence have no idea how many plants to buy. Would it double in size in a year? Quadruple?

[Trillium]

Here's a good reference that should answer all your questions about horny goat's weed, aka, epimedium

http://www.bbc.co.uk/gardening/plants/plantprofile_epimedium.shtml