There are a lot of natural herbal ways to keep plant predators out of your garden. Through the natural processes of evolution, plants have mastered the art of symbiosis and pharmacology. They have found ingenious methods for creating phytochemicals which act as natural defense mechanisms. Wormwood for example, actually got it's name due to the fact that worms will NOT eat it, nor can they stand the scent of it. Other natural pharmacological gems such as Menthol from Mint, can also keep critters away from your garden.
I also like to add Echinacea, and Yucca root tea to my spray bottle because it seems to prevent any type of uncommon yet undesired fungus, etc. To prevent ants from invading your garden space you can conjure up a mixture of molasses and orange oil, or lemon oil. It will literally kill them. I hate to sound so cruel, but who likes fire ants? If they're minding their own business, cool.. but as a child I was bitten all over by the little $*%^! and I can tell you, it wasn't fun. You can buy a pesticide sprayer and add the tea to it just make sure you filter out any plant material or you'll clog up the spraying mechanism. After it rains, you'll need to reapply it. These plants can also repel chiggers, which is a plus. If you have your greenhouse or crop out in the woods somewhere, then you'll run into them and it's not fun at all.
I have to keep my blogs kind of laid back.. because if I say too much about phytochemistry, certain individuals don't like it and they find ways to affect my life over it.