This current grow, I have one plant that was showing signs of potassium deficiency in flowering so I’ve been adding small amounts of potash. If there isn’t a deficiency don’t add it… it can affect the plant’s ability to uptake nitrogen (which in flowering isn’t a big deal).
Depends on the reasoning I would say. Potash isn’t the only source of potassium either. You could easily raise potassium availability through top dress and/or teas.
If it’s straight up pot ash from a fire place
A hand full will shoot your ph through the roof.