I'm not sure, but if you're in California, maybe you can call your local extension office and see if they have more information about it, since they're directly connected to the UC system.

Check this out. I dunno if this is "the" UC mix, but there's a variety, so I guess you could trial and error it until you figure it out.

Here is a link that might be useful: UC soil recipes

It's actually called "CU Structural Soil" and it was developed at Cornell University. Here's the full story on what it is and how it works.

Lots of people are coming up with their own version to get around the fact that Cornell holds a patent. People try to modify the material just enough to get around the liscencing, but still make it similar enough to the original material that is works the same way. I've seen some work okay and I've seen some real crap that absolutely bombs under real world conditions. They won't tell you that though. They'll tell you it's different because it's "better". With a little digging, you'll find that the "researchers" are linked to someone selling the material under a different name. Often, it's the same company or person.

According to my resources, the 'standard' UC mix (developed in 1986) is as follows:

80% pine and bark fir
20% sand

Added per cubic yard of mix:
2 lb single superphosphate
3 lb Dolomite lime
3 lb calcium carbonate lime
1 1/2 lb iron sulfate
1 lb calcium nitrate
1 tsp copper sulfate
1 tsp zinc sulfate

But I also located references to various other UC sponsored formulations so I'd suspect the mixes have changed over the years and are customized to specific growing situations. If this is a mix you want to use, then I'd also suggest confirming with your local UC extension office for their current recommendations.

CU structural soil is not UC mix. Homer's link is what we used in Greenhouse Culture at UCD, according to the plant needs.

Dan

Well, that's not true at all :) There are multiple formulations for UC soil mix. And all involve more than just peat and sand.

Reference herein

UC put out a publication of all their tests. UC mix Is 1/2 peat, 1/2 coarse sand by volume. There are variations, but UC mix is a pretty standard Hort term and refers to the sand peat mix. Fell out of favor due to weight and shipping costs.

Research in the intervening years has disproved many of the assumed benefits of a peat/sand combo for potting soils and the original UC mix was discontinued more than 20 years ago. So it is not at all "standard" to those in the know in the container gardening industry.

One can do much better than a 1:1 ratio (or ANY RATIO, for that matter) of sphagnum peat and sand. The key to understanding why lies in the fact that sand as we normally think of sand is simply too fine to serve as half of any medium used for conventional container plantings. Water retention is driven primarily by particle size. Combine 2 fine ingredients in large proportions and the air porosity will be very low, as extremely low. Even if plants grow in it, they wouldn't exhibit as much vitality or growth (all other cultural influences conditions assumed favorable) as plants in a medium with greater air porosity at container capacity (like 'field capacity but for containers).

Al

Here is UC web site and YEs, the traditional sand peat is still a "thing". We use it here in the southeast with incredible success.