There's two common methods you could comply with to soak your pots in fertilizer to age them. The first way is by sealing the drainage hole in the pot using a wine cork or wax, filling the flower pot with the fertilizer mix, and permitting it soak for 1 week. https://potsflowerpower44332.blogdon.net/aged-terracotta-pots-things-to-know-before-you-buy-44242618