If I remember correctly, it is around Summer - September.

Best to double check with other GoYers.

September's a great time, germinates fast, grows quick, settles in over winter, but you can do it from March onwards. Takes longer to germinate earlier in the year, that's all.

We sowed a patch at the end of October (having had to wait for some work to be done); quite surprised to see it growing well. Sorry if you've missed the boat this time, but the soil really is too cold now. Good luck for next Spring!