September onwards, so long as the plants are big enough. Keep watered during dry spells this month and next though.

Pardon, "dry spells", what are they Bamboo. I would love to see one but doubt that I will again this year.
Yes, Derek, plant out now as long as they are a reasonable size, say a nice fit into a 3" pot or larger.

Hee hee, sorry to laugh Bulbaholic - I know you've had it rough for some weeks up there. Its been pretty foul here till this week, and is still very cool, anyone'd think its the end of September, not the beginning.
I only mention dry spells because I often get caught out in late September early October - one tends to assume the plants will be fine, but if it doesn't actually rain for 2 weeks, then they can keel over, specially if the weather's sunny during the day. Down here anyway...