Q: Can I use fireplace ashes as a source of potassium for my roses?

A: Ashes do provide a slight amount of potassium for plants. They also counteract the natural acidity of soil, so they are a substitute for garden lime. Because ashes are so very alkaline, only a small amount can be applied at a time. Twenty pounds of ashes per 1000 square feet would be plenty to use at one time on a lawn. If you are preparing a new rose bed, two pounds of ashes per 100 square feet would probably be fine. I think I would be more worried that the potential harm from the alkaline ashes would be more than the benefit from their potassium. Sure, you could use a few tablespoonfuls per plant but you likely have more ashes than that.