[Colonel Flagg]

Use mineral oil - water is too light, and the petals would fall too quickly. Oil is more viscous and will allow the petals to lazily swirl and fall about the trunks. Mineral oil is also food-grade, so it would be safer than the topical variety. :rugrats

Also, I agree with ^^^ - don't soak it in water first, unless you dry the materials completely prior to filling and sealing. I think it would spoil the effect.

EDIT: Thanks Dex! I was looking for something like this.