Lol who knew carpet could be a touchy topic, Now I see both points but I think it boils down to like Gyro said, if you try it and it works then do it. if it dont work for you then try something new, I personaly wouldnt lay old carpet down for a number of reasons. The main one for me is
Yes this is true but I don't water my carpets everyday, the new stuff is made to be safer then old stuff but their also intended to keep dry and clean indoors, not moist and in dirt outdoors. If you get a major flood in your house and all you carpets are soaked, well guess what you can try to dry em out or you'll be getting a lot more carpet for the garden (if thats what you use).
This being said I have seen people using outdoor carpeting like astro turf or that fake green stuff which is for outdoor use it looks like it works great. I think anything that will breath and block out the sun so that only the plants you want to live you let poke through will work.
Sorry guys had to throw in my 2, again lol Friendly debate and it's bringing up many good points which in the end we might find some totally out of left field solution no one ever thought of.
"im spraying all mine down today with neem as i have aphids in the GH. need to get them ready to sell" Damn that sucks Mcpurps, have you ever tried unleashing a lady bug army or two in your GH? I got 1500 for my mothers last year when she had problems, the damn things are on a never ending mission for pests and water drops. Whenever they got them all they would just eventually leave, or die which ever came first. The trick is to keep em in your freezer and only take out what you think you'll need for the amount of pests you have. Or just let em all go at once they're only 3 bucks for 300, I also want to try raising praying mantises eventually dont seem that dificult you just need to find a non canibal species. A lot of people keep these as pets they're pretty neat and something I'm going to do when my sons are old enough to understand the growing process, some can even live in mason jar size container.
http://www.amazon.com/s/ref=nb_sb_ss_i_6_9/182-4883786-4381623?url=search-alias%3Daps&field-keywords=lady+bugs+live&sprefix=lady+bugs%2Caps%2C258