I had to buy about three different citrus with these funny codes before I came up with this sort of theory about what they mean. If I’m right then these are:
Improved Meyer Lemon on Carrizo
Oroblanco Grapefruit on Volkamer Lemon
Frost Owari Satsuma on Sour Orange
The Volkamer Lemon has a little rootstock sucker so I think I’ll grow that out and airlayer it off or root it as a cutting to propagate another variety on.
Dan
You nailed it. My mistake, the Clementine has the CLN and the Owari has FOW.
More detail: The first Owari I got had no tag. I went back and bought 4 trees - a Clementine for me (had a tag laying in the pot), as well as a Clementine and an Owari (with tags) and a dwarf cara cara (no tag) to put at my rental house. Kind of hit and miss.
Be careful putting anything on Carrizo in the ground here in Phoenix. Can’t take the salty water.
I wish Costco ordered from Sunset this year rather than buy trees out of California on lousy rootstocks.
It’s a tough call here in my locale. I spoke to a nurseryman recently about their stocking 500 (and above) chill hour trees for sale, and he mentioned that people drive from colder climates to purchase DWN trees. Makes sense if there’s staff on hand to ask where customers live, but otherwise it’s a recipe for failure.
Trees and pets are poor impulse purchases.
Our soil in the Phoenix valley is of a high pH (8.3), is calcareous and sodic (highly saline). I cant speak specifically to why sour orange is the rootstock that works here other than im sure that its more adapted to those conditions. And all the commercial groves and propagators in our area will tell you that they wont put anything in the ground here that isnt on sour orange.
Im sure a little poking around will net you the specifics on a maricopa country extension document online if your really interested.
Perseverance pays off. After about 10 visits to different Costco’s over the last 3 weeks, I found a Gold Nugget mandarin. It’s on Flying Dragon rootstock, so that’s perfect for growing in a container. 
Is this a national thing? Anyone know if Costcos in the Midwest do this bare root tree thing? Even with the big boxes it always seems there is some variability. In my experience there was always a difference between Iowa and Chicagoland for the same brand.
The Costco in Anchorage and Phoenix both carry trees in the spring time for their area. There are several threads in the Gardenweb forum with postings from quite a few cities about the Costco trees, so it seems to be standard practice. Citrus are always in pots, stone fruits and apples are bare root.
It varies. The two I have frequented , Waltham and Dedham, do not carries any bare root trees. The fruit trees they offer are potted blueberries, a few apples abd peaches, nothing exciting regarding varieties.
But again, Home Depot at different locations in the same state do not carries the same fruit trees, either.
In another thread, I was discussing that I had asked my landscaper to plant a Tangelo, but I got an orange of some kind and not a good one- at least the first major crop (4th year). Well, I was in Costco yesterday and found a Tangelo on Flying Dragon. So, it and a pot jumped into my cart. Now if I can just find a Tango… My wife thinks I’m going overboard. She’s right.
