Plant ash is not a universal pest treatment for potted plants. Identify a problem before adding material that changes the growing medium.
Identify the problem
Look at both sides of the leaves, stem joints and the growing medium. Record what is moving, where damage appears and whether nearby plants have the same signs. A flying insect near a pot is not enough information to select a treatment.
Leave household remedies out of the pot
Do not add mothballs, salt or burning mosquito coils to a plant container as a general pest-prevention routine. These materials do not replace a diagnosis or a product labeled for the identified pest and plant.
Choose a targeted response
Keep affected plants apart while checking the cause. Remove loose dead material and review watering conditions where appropriate. If a treatment product is needed, follow its label for the plant, pest and growing location instead of mixing household chemicals.
Related reading: Common Plant-Care Mistakes: Check Before You Change.