Many plants have natural substances in their roots, flowers, leaves etc. that can alternately repel (anti-feedants) and/or attract insects depending on your needs. In some situations they can also hel READ MORE http://www.ghorganics.com/page2.html
Companion planting is based around the idea that certain plants can benefit others when planted next to, or close to one another.
Companion planting exists to benefit certain plants by giving them READ MORE http://www.companionplanting.net/