a great website i use for essential oils is essentialoilsdirect.co.uk they are very reasonable. I have a great book on aromatherapy in the garden i will look at it at the weekend and share with you all on monday!
i used thyme and hyssop oil to deter slugs and flies in the greenhouse, it worked for a bit but then i got a bit lax and stopped doing it. i put drops of lavender and hyssop and thyme on newspaper and hung them from the greenhouse ceiling to stop flies, that was ok.
Jem