People sometimes choose to scatter the ashes of the deceased in natural areas. What is the effect of these cremains on the local ecology? Is there any nutrient value for the plants and trees on which they are scattered (such that one may rightly feel that the deceased has become part of the trees), or are the ashes just inert ballast that helps hold roots in place?
I’d imagine that actually scattering them wouldn’t be a big deal, they’ll probably mostly wash away the first time it rains. Leaving them in one clump (ie burying them) will render that area unusable. That ashes contain a lot of salt and a very high pH.
I could be wrong, but it always seemed that the most natural (as in eco-friendly) way to dispose of a corpse would be to bury it, just it, not coffin, no vault, no chemicals, just put the body in the dirt and let it decompose.
Well, the Feds think that there’s an impact. Under the Clean Water Act, cremains can only be scattered in a body of water at least three miles from land. Plus, you’re supposed to notify the EPA within 30 days after scattering them. (Note that this is only applicable to scattering cremains in a river, lake, or the sea.)
The most eco-friendly way is to leave it in the open, let it be recycled as scavengers and insects.
Here are the chemical constituents of cremains
It has around 50% phosphates which is a plant nutrient (N-P-K). I put phosphate fertilizers for most flower plants, so it is likely that a portion of the cremains will turn into flowers.
Not directly on point, but I read earlier this year about Washington possibly making it legal to compost the dead.
And I’ve looked into places that practice “green” burials.
My wife is not thrilled with my first choice of hanging out at the body farm!
My wife is convinced that I just want to ensure that I remain a pain in the ass even after I’m dead.
I joke about her having to go into the yard and manually crank the composter as my carcass clunks around inside! 
You could add a motor and add a belt drive. It would be like a rock tumbler. So the question is, would she rather go out and manually crank it, or listen to the constant drone of it all day and night?
I was not terribly concerned with the eco-friendliness of scattering cremains; it was mostly a philosophical question, i.e. whether bereaved folks can console themselves with the idea that their departed loved one eventually becomes part of the trees.
See sky burial, which is a tradition in Tibet and neighboring regions.
Or, she could just add some manure and turn me w/ a fork! 
Cremains contain bone fragments. If they’re not ground up sufficiently, they can contain obvious bone fragments; bits of skull, jaw, long bones that look a whole lot like a bone fragment. One ash scatterer described the cremains as “6 pounds of coarse sand and sharp bone fragments”.
These things don’t dissolve in the environment quickly or even readily; they won’t be washed away by a rain, it’d take a flood to move some of them along. And it’s prohibited to scatter them in certain areas.
Here’s a link to the do’s and don’ts of scattering ashes: https://www.perfectmemorials.com/guides/7-things-you-need-to-know-before-scattering-ashes/
When my dog died a few years ago, I looked into different options for his cremains. I wanted to plant a flower bush over them, but they are very very alkaline as mentioned above. I ended up just burying them in the yard. As QtM says, the “ashes” actually more like fish tank gravel and would not quickly disperse with the wind and rain.
Over the past year, the neighbors behind us buried a cat and a medium-sized dog in the back corner of their suburban yard right behind our fence. It is an area where water tends to gather, so I wondered if we’d see their corpses bob up thru the muck. As of late, there is a large varmint hole right in the same area. I’m guessing skunk. Wonder if Pepe Le Pew is down there nibbling away on Zuzu and Lulu?
To judge by my local crems and their gardens, I’d guess the ashes are good for roses, and there are a fair few other garden flowers that like alkaline conditions. I think my mum and dad would love it if they were pushing up roses and lilacs.
My mother was a keen gardener and at her particular request, we scattered her ashes in a woodland cemetery; it is a beautiful place and very well maintained. There was some paperwork: we had to produce a certificate from the crematorium to certify that the ashes had been properly dealt with, and, unsurprisingly, there was a fee to pay. We were not allowed to do the scattering ourselves either - they sent someone out with us to do it, but we chose the spot.
As an aside, our local crem uses their surplus heat to warm a nearby swimming pool.
That’s quite possible.
The first time we buried a guinea pig in the backyard, we looked out a couple weeks later and saw a hole where the pig had been buried. We’d heard of skunks and other small varmints digging up buried animals. Either that or the piggie is now a zom-pig. We did NOT mention this to the kids.
The next 2 times, we bought a bit of flat stone to put over where we buried the animal.
I just want to be buried in a plain wooden coffin. That way if they need to dig me up in around a year to do dna testing or such, no problem. But beyond that the moisture and worms should take care of the rest pretty fast. I’ve read where they have dug up old graves and all that remains is the metal coffin handles.
Nice going, so now you get a zombie pet with a headache.
Hmm, my father’s ashes, which were given to use in a cardboard box lined with a sturdy plastic bag, were ground to the point of just looking like coarse sand with a bit of gravel. We decided that it was better to avoid being caught than to ask permission, and scattered them as a family in a place we had legal access to, but might not have gotten permission to use in that way. We spread them around in several places, and you couldn’t see that we’d done anything when we left – there was no visible pile of ashes or anything, and the ashes looked pretty similar to the dirt and gravel that was there when we arrived.
I didn’t realize they contained so much phosphorus. I doubt it was enough material to do any harm, though, we weren’t at a place that attracts hundreds of people wanting to spread ashes.
When our pets have died we’ve just dug a hole and buried them. We’ve buried animals from the size of small parakeets to large cats. I think something dug up the parakeet, but the other graves all appeared undisturbed. I placed a piece granite that I dug up when making the hole at the head for each cat, by way of a headstone. I think of them when I mow over those stones.
Teeth, being covered with enamel, the hardest bits your body produces, can also be a feature.
Modern medicine being what it is, you can also get surgical screws, titanium parts, etc. When my late spouse was sent off to the crematorium I mentioned that he had a titanium rod in place of his right tibia and fibia. The funeral director sort of poo-poo’ed my concern. Then I got a phone call: “Holy cow, that thing is 18 inches long!” Actually, only 14, but he said it was the biggest surgical addition he’d ever pulled out of cremains. Clearly, THAT sort of thing isn’t going to decompose in anything less than geological time spans.
The funeral director also asked if I was planning to keep the ashes or scatter them. If you say “scatter” they’ll run them through the grinder a second time to make them finer and less recognizable as ground up bones.