On Jun 14, 5:32*pm, scrapmum
wrote:
Hi folks
I have just joined and I have a question for you that I hope you can
help me with. *
I have some stunning pom pom primulas which are getting very clumpy (is
that a real word)? *How and when do I thin them out because I have never
done this before?

--
scrapmum

I presume you mean Primula Denticula by pop pom primula.
When to divide is dependant on where you are growing them, if they are
somewhere damp and shaded then you can divide after flowering, in less
favourable conditions I'd leave it till the end of Sept.