I brought a grow bag from netto's this year, and it was rubbish. If it is the mostly yellow bag, leave well alone. I didn't have a problem with them last year but this year it was cheap and nasty, full of bits of wood, that looked as if it was creosoted, some wire, and also shredded plastic. I use this stuff as potting compost because it's cheap, and has worked well in the past. Don't get me wrong, this may have been a one off, and at 99p you certainly get what you pay for.