In some areas, coarse is not available, and people substitute medium. It seems to be acceptable. You could always mix the two to compromise.

Here is a link that might be useful: What's Growing On?

Thanks for the reply. I had considered that.

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.

Where is your garden located?

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.

Here is a link that might be useful: Vermiculite/perlite descriptions

I have mixed two 5 gallon containers just as an experiment and will plant two bush goliath tomatoes each in those, although I am considering going to a larger container, maybe 10 gallon just to have more room. I usually plant in 18 gallon but those have plans already.

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.

The depth of soil for a Square Foot Garden may not sound like much, but this lettuce was grown in a SFG on top of asphalt.

Here is a link that might be useful: What's Growing On?

Jay, especially if it gets hot where you live, I would have steered towards the smaller vermiculite in those smaller 5-gallon containers.

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