John koler from growing your green uses only compost in some of his foot deep beds and seems to do well

What is your underlying soil? I am over at least a foot of sand, so I get away with almost pure compost, but if you are on a clay soil, i would try to work in some vermiculite, even if not the full amount

@ray_scheel: It's clay and rocks.

Vermiculite is just painfully expensive (around $11 per cubic foot) and even if I went light with it, I'd end up spending over $500 for our size garden.

My dad, in Montana, just uses compost... no vermiculite or peat and his garden does well. He waters about every 3rd day when it is hot/dry.

In my raised beds I have the first 6 inches of 1/2 compost, 1/2 peat and 1/2 vermiculite. I will fill the rest with compost as my compost piles produce it.

Vermiculite and peat add no nutrient value to the soil. fwiw - I never added any to my beds.

I grew zucchini, chives, bell peppers, basil fine last year with manure and soil.

I originally did the recommended mix and regret the $$ I spent. I now go with compost added every year along with some garden soil, and wish I'd gone with a compost/soil mix from the get-go.

I think the vermiculite is really to help retain moisture, especially in raised beds ( more exposure to wind drying ) which are on hard bases ( no water available to draw up ).

I'd try it out for a season and see how you go - if you're heaping beds on top of existing soil I reckon the above advise will see you right. I've never had a problem with just compost.

Best of luck.

D