That's an important question, and I'm glad you asked before taking action. To be direct: no, it is absolutely not safe to put hot ashes in an outdoor trash can. This is one of the most common causes of accidental fires, even when you think the ashes are completely cool.
Here’s the best and safest way to handle them:
First, never transfer ashes directly from your fire pit, grill, or fireplace to any combustible container. Instead, use a dedicated, metal ash bucket with a tight-fitting metal lid. Stir the ashes thoroughly to expose any hidden embers. Then, slowly sprinkle water over them while stirring, ensuring everything is fully saturated and no steam is produced. Let the ashes sit in this sealed metal container for at least several days, but a full week is ideal, placed on a non-flammable surface like dirt or concrete, away from your house.
Only after this extended cooling period, when you can confidently place your hand on the ashes, should you consider disposal. You can then transfer the cold ashes to a heavy-duty bag and place them in your regular trash.
The key takeaway is patience. Rushing this process risks igniting your trash can, your home, or even causing a wildfire. Always treat ashes as if they are hot, because they can hold intense heat for far longer than you might expect.