Posted: 01/08/2016 at 16:39
Pokhim, they will expand quite quickly as JIMMY said So they will occupy an increasing amount of ground and neighbouring plants will be overcome.
if you have the space planting in 3's makes a real impact so, yes, 2 "clusters". Given their own bed, in the sun, they look impressive. They usually make multiple flower heads.
From a very large group in the garden I now have 4 clumps which are divided every few years. The large group simply took over....looked sensational in flower but for the rest of the year nothing else.