My answer (compiled from different places that I responded:)
That depends on who you ask. Robert Tisserand suggests refrigerating all of them. We do not refrigerate the Roses because it causes them to crystalize. (ditto aniseed.) this can happen at cool room temperature, as well. If it does, just sit the bottle in a cup of WARM water (think baby bath) for a few minutes to re-liquify. We don't like the idea of repeatedly heating an oil if we can avoid it, so we do not refrigerate those two.
The "base note" oils, the long lasting woods, roots, and Patchouli all improve with age, so why would you want to prevent that? I would never refrigerate those. Again, cool room temperature and shielded from light and direct heat.
|A friend shared her EO storage refrigerator. Now, THIS is a serious user. Most folks use an under counter/dorm sized box.|
What SHOULD be refrigerated are the citrus rind oils, orange, mandarine, etc., and the conifers... the "needle oils"... pines, firs, spruces, etc. They are the two shortest lived categories so definitely benefit from refrigeration. As for all the oil in between... that is preference. If you are going to be using your oils within a reasonable time, then, you could refrigerate, but it's not necessary. If you know you have enough.. let's say Lavender, to last you for 10 years, yes, refrigerate it, and store it under nitrogen. But if you buy what you need and replace it with the next harvest, then it is truly personal choice.
Something else, Lynette asked if any oils could be harmed by refrigeration. Thinking of how thick and "sticky" myrhh and vetiver can be... and if they were refrigerated...they would be.. think 'cold molasses." The shorter lived ones, and the Blue oils benefit by it though.
OH.. another thought. the distiller of our beautiful Frankincense sacra suggested that I NOT refrigerate her. She says that WINTER for those trees is, perhaps 68 degrees Farenheit and the cold would shock the oil. the resins do not have a terribly long shelf life, so, again, perhaps best to buy what you will use in a year or two, and then repurchase.
Regarding the Frankincense comment above. Robert Tisserand was kind enough to join the discussion, and said that while Patchouli, for example, does not need refrigeration, "I find the idea that Frankincense oil would be "shocked" by refrigeration a delightful one, but oils are not people. Any frankincense oil high in a-pinene or a-thujene needs cool temps to reduce oxidation." (We are storing our bulk Sacra (and other Frankincense oils) under a layer of nitrogen to protect from oxidation. You might want to consider both sides of this discussion in deciding how to store yours.)
Another thought. You can further protect the oils by NOT storing them in half full/half empty bottles. Decant those 15 ml bottles down to 5 or 2 mls as you use them up. that helps protect them against oxidation, which is their worst enemy.
Another participant in the discussion reminded us to keep child safety in mind. If you are storing your oils in your kitchen refrigerator, *please* store them in a locked safety box. Children are used to food and beverages being in the refrigerator. If you are able to get an under-counter or dorm sized fridge for your fragile oils, please consider padlocking it shut. Your child or a visiting child's safety is worth the inconvenience.
I love the questions we are asked!