The earbuds we use are unfertilized. If you want to grow an ear, you'll need to take your earbud and use it first to get your pollen (called wax) on it. Then you need to wait for some variety of Earwig - the natural pollinator of the ear - to approach and enter your ear cavity to deposit the pollen of a solo ear, like those found in the Forests of Flesh or the ones in the Caverns of Fragmented Kin.
Once the earbud had been fertilized by both sets of pollen, you can plant it in any planter made with a mixture of high quality soil, Onan's Sin, and Abomination Tears (if you can't make your own Onan's Sin, store bought is fine. It is recommended you gaze into the Hungering Sun to produce your own Abomination Tears naturally, store bought ones are rarely ethically sourced and overpriced when they are. Just don't stare so long your eyes become mouths, ha ha!)
When the ears sprout, make sure to play the appropriate melodies to provide them enrichment. The screams of the damned may be too much for young ears - try instead singing them from the Nth Psalm of She-Who-Craves-Agony. If you still have baby teeth around, you can grow a mouth using a similar process to serve as a companion for your ear! If you need the teeth, check any Fleshwoods market for locally sourced baby teeth. Don't forget to tip the Night Merchant!
tipping will only protect you from the Night Merchant if it's done in a spirit of community and friendship. if it's done out of fear or greed, or simply because you think you're supposed to, the consequences are unspeakable. that is to say that any text or speech giving detail on those consequences is retroactively removed from reality, and the hole it leaves behind is dangerous and easy to fall in to.
remember, entities from the dark have feelings too, whether or not they are people in the narrow way that humans tend to mean it.