Found it!! (Couch grass and marigolds)

[fosteri]

Found out about the marigolds on the compost heap!! Apparently if you chuck Tagetes Minuta (Marigolds) seeds on the heap that contains couch grass  their roots contain a  natural herbicide and not only do they kill the couch, but are also good at killing other bugs and pests too.....

Louisa xx

http://www.edirectory.co.uk/chilternseeds/pages/moreinfo.asp?Table=Product&RecordID=BFBCJGF 

Try this link....

[fosteri]