I don't mind at all going to bed with ashes on my forehead. This morning most of it was still there. I took a piece of moistened tissue and rubbed it off and threw the piece in the front yard where it will disintegrate into the dirt - after the snow has melted (yes, snow; those arctic winds sometimes like to come down and play games when the crocuses come up).
The reason I did that is because of a question that occurred to me: since we are not to dispose of holy water or any other blessed object in the garbage or down ordinary drains that lead to a sewer (such as showers), but are to either burn, bury in the ground or dirt of household plants, or wash down a sacrarium (special sink that leads directly to the ground for the washing of sacred vessels or contaminated holy water), wouldn't it be the same for holy ashes? They've been blessed.
Or maybe everyone has been doing this; disposing them in the ground. I know I haven't been.