I'm not an expert, so don't think that my word is any authority. I'll just tell you how I would probably do mine.

If you have clay soil under the bed, the amount of peatmoss should be good. If the soil underneath is OK, I would suggest using a little less peat and a little less mushroom compost and adding some fresh compost or manure into that mix. My reasons for that would be that mushroom compost is already "spent", meaning that a lot of nutrients have already been used up.

I don't know about the sand. I've never amended with sand myself because I've always found peat moss to be more than sufficient to loosen up soil.

What is your base soil that you need to add sand to it?
Why peat moss, a non renewable resource that the Royal Horticultural Society is recommending its members stop using?
The mushroom compost is all you need.

Wow Kimmsr.
Has anyone ever done anything that you approve of? I mean....ever? I bet you'd give Santa a hard time if you ever met him.
Santa: I give presents to all the world's children
kimmsr: Why? When children get presents instead of working for their toys, they get lazy. When they get lazy, they get out of shape, have heart attacks, die, fall to the ground, and become part of the Soil Food Web.
Santa: But, But, it's what me and my reindeer do.
kimmsr: Your reindeer? Why do you have reindeer? They produce more methane than a third world electric plant.
Santa: But at least I compost their poop for my candy cane trees.
kimmsr: How do you know you need reindeer poop? What's wrong with soil at the north pole? Did you do a Jar Test?
Santa: Well no, but I...
kimmsr: Stop using synthetic fertilizer!
Santa: I never said I used fertilizer, I was talking about.....
kimmsr: You're killing the planet!!! (head explodes)

Hamilton...are you a member of the RHS? If not, feel free to use peat. Canada does a good job of regulating this resource, and it is in no danger.

That said, and while I usually use peat in containers, I don't feel it does much to enhance garden soil. In your raised beds, I'd replace it with some other organic material which will break down faster, like shredded leaves, or some other type of compost.

Sand is something else. it adds a little bulk, and can improve drainage if well mixed, but raised beds generally drain pretty well anyway.

How about some plain old soil in the mix? Blend in at least 50% of a variety of composts, including the mushroom compost, and you should be all set.

Sorry, Hamilton, that was aimed at Patti.

Donn, I figured so.

I wonder when kimmsr is going to start boycotting mushroom compost? I mean, given that mushroom compost has peat moss in it.

Hamilton what is your source that mushroom compost has "peat moss", I'm assuming you mean sphagnum.

BTW, if one ignores everyone except kimmsr you will be well served.

esther opal,

Google it and check out a bunch of different sources. I did just that and found that with the exception of one, they all mentioned that peat moss was used, either as a primary medium, or mixed with sawdust, hay, etc. Add limestone and voila...mushroom growing medium.

The sphagnum is on the order of about 1% and horse manure straw compost (don't know why The American Mushroom Institute fails to mention the influence of horse manure) is about 95% or more. The sphagnum insignificant.

esther,

That depends on the grower.

Check the mushroom growers out. I'm sure there are some that will grow only on straw and manure, but for most growers the peat is cheap, efficient, and readily available. Most will go the easy route and use peat moss heavily.

I suppose you could always look for some sort of "sphagnum moss friendly" mushroom grower to supply the mushroom compost, I'm sure there are some out there if there is a market for it.

The truth is that mushroom buyers and mushroom compost buyers probably don't ask questions about where their growing medium comes from.