Growing Soil or Importing Soil?

Hello!

I am in a situation where we have about one foot of topsoil, and then we hit bedrock. I've looked into buying soil, but it seems to be very expensive! Any tips on places to find cheap soil, or cheap compost ingredients?

My other thought was to grow my own soil by sowing plants that produce large amounts of biomass, and then using them to create gigantic amounts of compost. I may have to add nutrients to go this path, but it seems to me like it would still be less expensive; however, it would of course be a lengthy and sweat intensive process. Any suggestions on which plants to grow?

The land is relatively flat, so I could mow it fairly frequently and collect the clippings.

Thank you in advance for your ideas!

If you can get free horse manure you can make a decent compost easily. Often you can find stable bedding which works fairly well. It is a mixture of straw, sawdust or whatever the stable owners use as bedding plus manure (and urine). Try contacting people with horses/stables. Some municipalities have piles of the stuff that people dump. Often you can get this for free and it often it has been piled for a while and has started composting already.

Growing biomass to increase the soil volume will take a long time. The biomass breaks down fairly quickly - generally you can grow slightly more than is consumed if you try. So the net gain is small year to year. It is worth doing, but you shouldn't expect big gains.

I'd make a "WANTED" post on FREECYCLE.ORG It's a great site revolving around free stuff. Love it.

Why do you need more soil?

Is it to store water, if you mulch you can slow down the evaporation rate thus you would have more water.
Also a lot of tree can grow with very little water (drought tolerant) so choose your species/cultivar wisely.

Do you want more soil to hold more nutrients?
Nitrogen in produce by living organism just make sure that 25%-40% of your garden in covered by Nitrogen fixers eg legumes.
Your bedrock is really just a huge store filled with mineral,
So as long as your plant's roots(including symbiotic fungi) can make it down to it, they will get the minerals.
Fungus/mushrooms do a great job at using acids to dissolve the bedrock for mineral in exchange for sugar from the plant roots.

biomass does not really stick around in the soil for long esp new growth like what you are talking about.
You best bet would be biochar. After creating the biochar maybe you can then mix it in in a 1 to 1 ratio.
But I am pretty sure that would negatively affect the plant.
Healthy soil is 25% water + 25% air +5% organic matter +45% minerals.
So the best way to increase the soil is to make it more porous so that it can hold more water and air.
Daikon radishes sound like a job plant for the job.