I just found a local supplier of vermiculite, a garden supply, and they have it in medium in 4 cuft bags and course in 2 cuft bags marked "square foot garden".

I know coarse is recommended but the thing is the 2 cuft bag of coarse is 17 bucks and the 4 cuft bag of medium is 19 bucks. 2 more dollars for twice the amount except it is medium.

Is the medium acceptable? I see where some people use it.
I have a hard time justifying the coarse when I can get twice as much in medium grade for only 2 dollars more.

Thanks for your consideration.

I am just going to experiment right now with a few containers of the mix and see how it works this year before I decide to go for it with a full blown raised bed.

The mix is intriguing with no fertilizer needed etc. as well as not a lot of depth required.

Really need to pick up Mel's book.

The only differences between the various grades are going to be in the aeration, compaction, and water retention.

I found this on a manufacturer's website discussing vermiculite sizes:

Much like perlite, vermiculite grades will provide more aeration and drainage if they are larger, and more water retention if they are smaller. Because smaller or medium grades of vermiculite will compact and hold so much water, they are ideal for seed trays and some propagation mixes. Glitter grade is used most often in peat mixes and potting soils, and larger grades are used in special mixes where more drainage and aeration are desired. Because of its excellent cation exchange capacity, vermiculite often is used to enhance the performance of fertilizers and other additives. For outdoor use generally perlite is better, but still many people do use a variety of grades for outdoor applications.

I don't think that the medium grade vermiculite will do any harm--in fact, I think that was the size I ended up with when I built my beds ten years ago and I got NO COMPLAINTS from the plants. If your summers tend to be hot and dry, the medium grade might even be better, especially in raised beds.

If you are worried at all about sufficient air spaces in your mix, then I might look into adding some coarse perlite, but I've never found that to be an issue.

I used coarse for those containers. Like I said, just experimenting right now to see how they will turn out.
I have been growing in the 511 container mix and was interested in the Mels as it seems to be more like regular soil and not a bark mix.

If they do well I could see making a raised bed and since that would take a lot more vermiculite Id sure want to be as economical as I could be as long as the mix would do well.

I appreciate the replies.

In containers, I think the goal of water retention outweighs drainage.