Would I be able to use lavender essential oil instead of the buds?

Hi Camden, to second Marie, essential oil is significantly more potent than lavender buds so you can use it but I'd use it in much smaller quantities. Something else to consider - you'll be adding oil to a buttercream recipe that wasn't written with that in mind. To make sure your buttercream comes together you may want to modify the recipe slightly - you could compare to a recipe that uses oils like this one: http://blog.gygi.com/blog/2012/08/07/faq-can-i-use-lorann-oils-to-flavor-butter-cream/

Hope that helps!

That stuff is highly concentrated, so I think it may throw off the flavor of the cake. If the lavender oil is labeled as edible, that would be okay.