Hello Siouxzn!

About a month ago I purchased a bag of Cedar Grove compost as an addendum to homemade container mix for my patio garden. No plastic bits, just rich, black compost. I had the same concern. I read product reviews on Home Depot and Lowes websites'. From what I can tell, the more recent reviewers seem to report no plastic bits. Cedar Grove has likely improved their process over the years.

Hope this helps. Cheers!

You don't want just compost - far too much organic matter and no mineral soil contribution. Will shrink and compact excessively during the growing season and may very well retain too much water.

Both Pacific Topsoils and Cedar Grove blend planting mixes that combine compost with sandy loam and usually some sort of drainage enhancer. These are perfect for raised beds and sometimes go by the name of garden mix or 3-way mix.

And with that quantity of soil needed you want to buy in bulk for sure!! Bagged products will be 2-3 times the cost of bulk soils. And when you need multiple yards, that adds up fast.

5-6 cubic yards of 3- or 4-way mix can be had for under $200 at various places.

I calculate over 8 cubic yards for the dimensions you listed.
7.5 cubic yards is one "unit", likely the most inexpensive way to purchase.

Thank you for the input guys! I did get a quote from Pacific Soils for the special garden mix.
Larry, I have some fill that I am putting into the planter at the bottom, so I wouldn't need the full 8 yards. But it is just a guess at this point, I won't know until its done (I have the block showing up tomorrow).

It is going to be a busy weekend building this thing!