This is a downloadable PDF image showing plant compatibility. 350Kb
You will probably need to zoom in to read some of the labels.
http://permaculture.org.au/2010/07/30/companion-planting-guide/ Some plants grow better around other plants and some are NOT compatible with each other.
The chart shows a "smileyface" for compatible and "x" for antagonistic relationships.
Recall the native American nmenonic: "The three sisters, Corn, Beans and Squash" which are
planted together because they all grow better in company.
Include on the right side is a list of pest-control related plants and plant extracts.