filling a large raised bed on a budget
I am building a large raised bed across the length of my back fence (about 70' long, 4' wide, and 2' deep). Because I'm not a millionaire, I'm looking for thrifty ways to fill it. I found a farm that will give me their horse manure, but I'll only have a couple of weeks for it to age before I need to mix it into the bed.
I have come up with mixed opinions online of people saying that horse manure would burn or isn't a problem fresh. If I mix it down to 50% or less with other stuff when I put it in, and wait a week or two before planting seedlings, what do you think?
I also have a message in to what I think is a local mushroom plant... but i don't know if they grow the mushrooms here or just process, and so I don't know yet if they will have compost...
I'm thinking about filling the bottom with the cheapest gravel I can find, and throwing in some wood that was around the yard starting to rot. I also have lots of leaves and pine needles that I might bury... but none of it is decomposed yet, so I don't know if it would be problematic to have it decomposing underground while plants are growing or helpful?
My only gardening experience previously was in Hawaii, where anything grows any time of year anywhere you put it... So I'm a little nervous about trying to make a successful vegetable garden in Nevada. At least I have lots of trees, so it won't be the dry heat that it would be otherwise.
Does anyone have any other recommendations? Are my ideas all terrible and I should chuck them out and go with something else? Any help or advice will be greatly appreciated!