human ashes also contain an extremely high amount of salt, which is toxic for most plants and can be leached into the soil.
Can plants grow in human ashes? Unfortunately, the answer is no, not very well, although some plants may be more tolerant than others. Human ashes are also bad for the environment because unlike plant matter, ashes don’t decompose.
Read more at Gardening Know How: Planting In Cremation Ashes