i've found that with heavy soil it isn't too hard to make your own peat like materials if you can get any leaves, sawdust, twigs, small pieces of rotting wood, bark, etc to bury for a few years.
i originally did this sort of thing to use the organic materials as a filler to perch gardens higher to get above flash flood stage. it also gave some improved drainage. since there are so many gardens here i don't always get back to a spot i've buried things for several years.
in one garden i was renovating this past summer i found a seam of materials i had buried four or more years ago. it was down about a foot and a half to two feet. when i dug it up it looked exactly like peat moss except it smelled of methane and bog. if i'd have lit a match near it i'm sure it would have flamed.
i don't have access to coir for free (which is how i prefer to get organic materials to use as mulches or filler for perching). we do get some wood chips delivered by tree service people or we haul some ourselves if we can get access to a truck. with as many gardens as we have there's no shortage of work needing to be done so not every garden gets a fresh topping each season or sometime for several years.
by the time the woodchips have mostly decayed and start sprouting a lot of weeds that is the sign that they are ready to be used in a vegetable garden as a nice amendment of humus. some of this humus will be scraped up and used in my small scale worm farm:
i use these to regenerate garden soil and also to do our food/paper scraps composting. it's been a great hobby since 2010. we don't keep any other animals so they are the way to complete the cycle as much as i can with our limitations. a lot of fun studying decomposition and the soil community.
I think I need some more sawdust. Ideally to let rot awhile.
it is my most questionable material (other than leaves i've not raked up myself or uninspected municiple compost (which i won't use ever again)) and i won't take a lot of it at once. i had a friend bring me barrels of mixed sawdust, wood chunks, rotting wood and bark pieces and that all combined is very useful. i can use the larger pieces of bark as mulch or to cover edges of exposed soils on temporary raised beds and such. the rotting stuff i can leave along the north hedge to get picked apart by raccoons and other creatures who like to do that sort of thing. small pieces of everything and sawdust and leaves and general detritus all worked well for getting buried.
depending upon who's doing the sawing and how much or what kind of lubrication they are using on their blades... i'm sure the soil bacteria can cope with a few petrochemical residues here or there but i don't want to overload a garden with them.
i forgot to mention my most important reason for burying some organic materials down deeper is for making worm refuges so they can find a place in the summer heat or winter cold that has some oxygen and moisture. in our normal subsoil in a new garden i may not find much worm life at all, but once i get a chance to work on it a bit and to innoculate for a few years with the worm compost then i will start seeing a worm population return. the main reason for not finding much worm life is that most of the older perennial gardens were installed with weed barrier fabric which prevents worms from getting down into the subsoil. once i get that out of the way and start mixing in organic materials then the worms have a better chance of things. still i like to poke organic materials down a foot and a half at least to create such refuges.
I used coir to start seedlings when it was first available here around 2000. Got lots of mold and never used it indoors again. Only have used it since when I get free broken bags from local garden center. Then it's added to the compost tumbler.