If there are years of ash build up the soil beneath may be too alkaline? Best to get a soil test before going forward, A pH of 6.5 is good for most plants.

We don't have free soil tests here anymore and it is such a small area that it wouldn't be worth it to send one out, so I'm just going to plant it and hope for the best.

The previous owners may have built the fire pit for looks as they did with the raised garden bed (which they filled with construction rubble and I had to have emptied and re-filled with decent soil)

Can you show a photo of the "fire pit" you're talking about and guess what might have been burned in it? If it was built 'for looks' then it's probably not a spot to burn yard waste, as I'd imagined. lol!

If you dig out the fire pit to a depth of 18-inches or so, and refill with decent soil, I can't imagine you having any problems, if it was really just used as a decorative wood fire pit. There is nothing in those walls that is going to hurt anything. Any residual alkalinity in the soil will leach downward, rather than upward.

Dan, thanks.

Party, no, I don't have GW on my phone, so can't do photos. lso it wasn't for yard waste. Probably wood.