On Monday, 12 August 2013 11:52:46 UTC+2, Windmill wrote:
Does anyone know how long glyphosate takes to kill various weeds?

E.g. elderberry bushes, dockins, brambles, bracken, grass?



Don't want to waste money by spraying again if it's premature to do so.

Seems to vary enormously. About 10 years ago, I would use Roundup against broad leaf weeds on a hot day and see them visibly start to wilt within 2hrs at most and they'd be flat out dead in a couple of days. Try using today's Roundup formulation, however, and you'll be lucky to achieve any knockdown at all.
I have give up with Roundup and Weedol. I buy some cheap stuff from Wilko in sachets that is supposed to be watered down, but I apply it neat. Still takes about 2 weeks to kill the weeds off, though.