If you alredy have loam why would you want to spend money on something called "topsoil" that most likely is not nearly as good as the loam you have? Are there no leaves from deciduous trees that you could use in place of that valueless peat moss?
Bamboo seems to want to grow in soils with a pH in the 5.5 range so is adding wood ash really a good idea?
Before adding some kind of nutrient source hav e a good reliable soil test done to see if that is even needed.

If you are trying to make a raised bed that stays raised, you are in an unusual position for a composter.

Usually, we seek out materials that break down quickly, but in your case you need things that break down slowly, otherwise your raised area will quickly sink down to the normal soil level.

Your plan to use quite a bit of native soil and crushed rock sounds good. I would also include sand since it's cheap, won't break down, and makes it easier to dig when you're going after out of control rhizomes.

Peat moss and pine bark fines go into the category of things that don't break down quickly. You might want to include things that take even longer to break down like pine bark nuggets.

Also, good luck keeping running bamboo in check without putting in an underground bamboo barrier. It can be quite a struggle.

Growing bamboo in a raised bed will not make it easier to control.

I haven't grown bamboo but it sounds indestructible so I wouldn't think you would need really fabulous soil for that.
Assuming you still want a raised bed in light of rhizo's comment, it will stay raised with more soil and less organic matter as billums pointed out. So use lots of mineral soil and less organic matter in your mix.

Organic matter, 6 to 8 percent is optimal, is what plants get nutrients from so many people not cognizant of the role of organic matter in soil will tell you to put in materials that will not "break down" quickly when you realy want the soil bacteria to digest that material so the nutrients they have will become available to your plants.

Just so. poaky didn't say what the planned ratio of materials might be, so it is worth mentioning to use *some* compost but not too much here.

From what I've heard about bamboo, it could become invasive on the Moon if it could find a way to get there.

I really would love to plant the bamboo in a huge pot. Which was what a raised bed would be, but I would add rhizome barrier around the sides. My wanting to add lots of OM is because, I thought mostly native soil in a big container (raised bed) would be like putting native soil to pot up flowers etc in a patio pot. I thought it needs to be light and have some fluffiness to it. If I only need loose areated soil in enclosed pots and not raised beds I won't need to improve aeration in the raised bed. I should have mentioned the reason for adding the OM, was to replicate potting soil and adding it to a raised bed or giant pot. I can use the OM for pickier plants and veggies etc. If raised beds don't need soil that is like potting soil instead of native soil, I won't need bunches of OM, but can add some of course.

I will need to buy some topsoil to make the bed higher, I don't have any spare native soil to add to it.

If the raised bed is atop soil and the bottom is open, in other words not on a concrete slab, drainage will not be like a container. Now if you place a plastic barrier under the raised bed to contain the bamboo, it will act like a container.

One thing I learned here is how different pots are from the ground as far as growing plants. I still don't understand it completely, but the main point I got is, soil generally doesn't work in a pot, and you don't need potting mix in the ground. :-]

There are bamboos that don't spread.

Jonfrum, I have clumpers already, but wanted to grow Black Bamboo. Phyllostachys Nigra. I have a big yard but want to control the spread of the Black bamboo. My soil is loam with clay underneath, but there are MANY small sandstones in my soil. It makes digging very tough. So I am hoping for the least Labor-intensive method.

I am saorry if I left out important details. My mound would be unrestricted in depth, but RESTRICTED in width and Length.