it can make your plant mold.Why,idk lol thats jus wat i heard but ive seen alot of cardboard grows
and they all look fine jus dont burn ur house down lol but how big are they?
idk if this will work outdoors but boil sum choped up garlic,onions nd red peppers then strain nd let cool nd put in spray bottle
works great for my indoor plants i had spiders nd nats havent seen one since..