I've used old wine bottles turned upside down and tapped into the soil. Pic
at : http://www.ljconline.nl/garden/gardenfront.htm
They have been in place now for 11 years and nor a single breakage!
it takes a while to drink enough wine though..............hic ....... "~)
Jenny

Now there's an idea...liked the pic too....people will talk but
hey...many thanks for that )
LW