Speaking of that, what IS your city?

There's not thing one wrong with old mushroom compost. Price, maybe (I'm sorta cheap). Could you explain how you came up with the one cubic foot figure? You said you need to fill the beds and if one foot will do it then they must be shoebox sized. As an example, if you have two beds, each four foot by four foot by ten inches deep, then it would take one cubic yard to fill them. What's in the bed now? All sorts of questions!

This post was edited by grubby_me on Fri, Jan 30, 15 at 21:24

1 cubic foot is not much, a 1 foot by 1 foot by 1 foot cube. A cubic yard would be someth8ing on the order of 3 feet by 3 feet by 3 feet.
Spent Mushroom Compost can be a good addition to any gardens soil, a soil amendment. It is not meant to be the soil, however. You would want a soil that is about 45 percent sand, 25 percent clay, 25 percent silt, and 5 percent organic matter,
Where in the United States are you?
USDA Plant Hardiness Zone 9a means little except which plants could survive a normal winter in your area.

Check craiglist in your area if you can find free compost

You do want some soil in there because pure compost (although plants may grow fine in it) will continue to decompose and shrink, and you'll have to refill. Sometimes pure compost can act weird too, such as getting crusty and not absorbing water in hot weather, or being too porous and draining too fast.

You could mix about 50-50 topsoil and compost, then just amend with a bit of compost each year.

If you need as much as a cubic yard, you might consider buying in bulk. If you have access to a truck, get it by the scoop at a local soil place or nursery. They often have a 'garden mix' which is topsoil and compost blend. Some may even deliver. Check the phone book, Craigslist etc. for places that sell in bulk. The money you save compared to bagged products might pay for the delivery, too.

I wanted a series of 12" deep raised beds. After realizing how much it cost to fill one bed with bagged compost, I filled subsequent beds with leaves, grass clippings, kitchen waste any kind of paper I could get my hands on, waste from the first bed. I was surprised how quickly the material accumulated. I topped it of with a layer of compost and was good to go. The garden did well. My family ate well. So did the worms.

Very few places that sell something called "topsoil" or "garden soil" will have a mix that is 50 percent organic matter and 50 percent mineral. If you are lucky you might find someplace that has a mix that has 5 percent OM.
Keep in mind that bringing soil in from outside may include soil borne disease pathogens. The same issue of Fine Gardening magazine that has the very good article about mulches has a good article about soil borne diseases.
Keep in mind that compost is partially digested organic matter, vegetative waste. Compost is part of the organic matter that all soils need, but the amount of organic matter in soils should not exceed 10 percent.

thanks grubby_me, it's definitely hot and dry here for most of the year but gets down to mid-20's in January. I'm planning to set up a drip system on a timer.

Obviously, I made a typo and it's a cubic yard and not a cubic foot. I don't have access to a truck (unless I rent one?). I definitely need to buy in bulk and hopefully from somewhere that has delivery. i guess my question is what is my best option for getting bulk soil/compost whatever? And what mix that's readily available and not expensive should I look out for?

I think I answered that in my previous post - including what is usually offered and where to find vendors who deliver. Can't help you much more than that as we still don't know if you are even located in the United States.

Grubby, I learned that soils should not include more than 10 percent organic matter from the soil scientists at Michigan State University and from over 50 years of growing plants.
A good garden soil mix around here, a mix of about 45 percent sand, 45 percent clay, and 10 percent organic matter, costs $16.00 per cubic yard plus a $25.00 delivery charge.

"...soils should not include more than 10 percent organic matter ..."

"Organic Matter" is what you have left when composting is completely finished (i.e. it's humus.) It is NOT the same thing as organic material which is what we use to make compost or in fact compost itself.

"Organic Matter should be 10% of soil" is by WEIGHT not volume. In general minerals are very heavy and OM is very light. By volume 10% is a boat load of organic matter. Think feathers and lead (OK, maybe not that extreme.)

Consider that as much as 90% of organic material "disappears" in the composting process--you need a boat load of compost/material to create just a little stabilized OM.

My very non-scientific conclusion here is this: Add boat loads of compost and hope that someday you might approach a good % level of OM. I agree with whoever said we are making this more complicated than it needs to be.

I agree it would be very easy for a layperson asking questions about soil amendments to be confused about soil organic matter lab results vs. volume of compost mixed with topsoil to make a garden bed. They may tend to equate them when they are not the same.

I have posted before (so the regulars can tune out here) that most compost is about 50% by weight water, to start. Of the half that is solid material, only a portion is organic matter (humus). Some (a lot) of that decays away after mixing into the soil. Only a tiny fraction of the original compost becomes Soil Organic Matter. So mixing 50/50 compost and topsoil does not give you 50% OM in a soil test the following year.

I'm not convinced that soil OM levels over 10% are so bad as kimmsr suggests, but there's generally no need to try to achieve that level either. It is a good benchmark to bracket the desirable range (5-10%) when deciding how to amend your soil.

""Organic Matter" is what you have left when composting is completely finished (i.e. it's humus.) It is NOT the same thing as organic material which is what we use to make compost or in fact compost itself." Not quite.
Organic matter is the vegetative material that is put in to compost or is added to soil to become the humus which is the residual organic matter left in soil when the soil bacteria are mostly done digesting that organic matter.

Too much organic matter in soils can cause too much moisture retention, ie. a soil that is too wet. To get an idea of what Ma Nature considers the optimal level of organic matter in soil go out into the forests and sample the soil and measure how much OM is in that soil. Most all soil scientists will tell you that optimal levels of OM in soils is 5 percent.

"Organic Matter" is what you have left when composting is completely finished (i.e. it's humus.)"

"Organic matter is the vegetative material that is put in to compost"

With all due respect this post is confusing and self-contradictory. I know the differences but people coming here to ask questions will be further confused.

As far as matching forest soil in our gardens, it may work fine, but we're growing vegetables, not trees. Not only that but forests and their soils vary considerably across the globe. Plenty of folks have posted here over the years that their raised beds of essentially 100% organic matter (container mix, compost etc.) grow spectacular crops. I don't advocate that (quite the contrary) but I also don't dismiss all those reports at once by saying it can't possibly work because forest soils are only 8% OM.

"Not quite. "

OF COURSE it isn't "quite" right--but that has more to do with you being you than me being wrong.

If you are going to use the words "organic matter" to mean any compost, any vegetative material that can still be broken down then you are completely misleading people when you start talking about Organic Matter (OM) as a percentage of you final soil composition without clarifying the difference.

I visited this forum quietly for over year thinking you preachers of 10% organic matter in soil were bat poop crazy. If I only mixed compost--what's generally being referred to as organic matter around here--into my soil so it was 10% of the finish deal I'd still be using a pick ax to break up my clay soil every year! Obviously, I have since figured out what you're trying to communicate, but I'm so glad I just ignored that part of the advice.

It doesn't matter if you are technically right, if you aren't communicating clearly.

subk3, if you think my explanation confusing try a dictionary. Perhaps the link might help some.

Here is a link that might be useful: organic matter

YIKES!!!!!!!! Nancy

So no response to my post pointing out the inconsistency in your definition kimmsr?

Can you clarify that you recommend when making a mix for a raised bed that only 10% compost should be used? Am I correct on this? If so I think you are alone on that. % Compost mixed into soil does not = % Soil Organic Matter in a lab test.

How do you report SPAM nowadays??

Oh, I got it, there's a little flag at the right. I reported both of you lowlifes. :-]