Packed dirt will eventually be overgrown by nearby grass or [[tree]]s, but not as fast as [[dirt]] would be so, in effect, packing the tile will slow the growth.
You are not able to pack dirt that is submerged in water, however it appears that packing dirt with one edge submerged is easier on South-East facing tiles, requiring the submerged edge to be completely raised out of water on NW facing tiles to work.
With Body strength higher than 21, you are able to pave a tile, then dig it into water to completely submerge it. This technique appears to be commonly used for Ship docks/Harbours to ease the exiting of the vessel onto dry land.
[[Mycelium]], [[moss]] and [[enchanted grass]] tiles can be changed to packed dirt with a shovel.