Thank you all, lordkiwi, Graftman & alan for your input!
The votes are all for Shiro, so I will get a Shiro online then.
I am planning to get it from Rolling River, because they carry Gold Nugget loquat too. I can get both from the same nursery to justify the shipping cost $32.60. 
Perhaps a bit late to chime in here, but in our area I would not grow Santa Rosa, it is too unreliable for fruit set. Weeping Santa Rosa is good though. Shiro is somewhat prone to black knot but it is not as bad as Methley.
I like yellow plums but I heard this one is not that good. I would probably get Toka as it is a universal pollinator. Said to pollinate Japanese and even American plums. Itās called the pollinator plum. It thrives on neglect, a strong grower and heavy producer. And the plums are excellent. Superior is another. These are plums for more colder zones, so not sure how they will do?
Here is a blurb from the University of Maine
āAsian plums are susceptible to two difficult problems that are managed by selecting good varieties. When rain occurs as fruit ripen, the skin of some varieties will split open and cause fruit decay. Shiro, Methley, Elephant Heart and Superior are prone to rain-induced skin cracking. Toka, Vanier and Obilinaja are less prone. The second problem is susceptibility to the disease black knot. The disease black knot can infect many varieties, but Obilinaja, Superior and Toka resist infection to a greater extent than other Asian plums.ā
Youāre going mail order. Universal pollinator, resists black knot, it can be just a rootstock, but in areas where people get low plum production, Toka will produce, known for this.
Toka is Prunus salicina x Prunus americana
They list Shiro first for cracking. Toka as less prone.
The only āissueā for Toka is how it tastes. Some people can taste its ābubble gumā taste, others donāt.
I did taste a hint of bubble gum on my Toka. Thatās why another name for Toka is a Bubble Gum plum.
Some people are turned off by the taste. Others like it.
Probably true for Shiro too. Not a lot of high praises for it.
Speaking of multi-grafted trees I have this unknown pluot seedling, I had 8 of them, one was purple leaved! Mites got into them, and this is all that survived. It was stunted and barely grew last year. Itās going into a 30 gallon root pouch in a few days. Iām going to use this for a multi-grafted tree. I harvested a small piece of Spring Satin. I love this plumcot. Iām going to make a micro-graft unto this wee little tree. Iāll try again next year if it fails. Iāll add more down the road. Dead leaves are from last year.
I have other mature multi-grafted plum trees. If youāre looking for scion, I usually have something Iām pruning!
Shiro can be very good in the right condition i.e. dry spell during ripening time and people let them hang to fully ripe. They turn yellow for several weeks. If you pick them too early, they donāt taste very good.
I have Shiro for many years. Dry years, they are very good. Wet years or a lot of rain near ripening time, not that great. But that happen to most fruit any way.
True! i went with Vermont for a yellow and Flavor Queen. Which is a huge fruit! FQ is often dogged too, but I find the no tart skin and coconut like flavor fantastic myself. Oh I also have Inca. Introduced by Luther Burbank in 1919.
But Scott is right about black knot. I just took a chunk of Bknot out last week.
Still, it is not bad as Methley of my firendās which was covered with BK. That tree was gone.
I noticed that Toka was mentioned as a universal pollinator and I have read it elsewhere. My Toka is the last to blossom with the exception of E plums. In the picture the left branches are Toka. It is a multigraft tree with some done, some blooming and Toka about to open. It might be universal in some places but not for me.
Iāve noticed that in a colder zone like mine, fruit trees of same kinds i.e. all J plums including hybrids and pluots) have overlapping bloom time (I have 10+ varieties).
Euro plums bloom about a week behind J plums. All of my Euro plums have overlapping bloom time ( I have 10+ varieties grafted).
Same goes with pears. Euro vs Asian.
I also have read here that in warner zones, bloom time does not always overlap.
@Graftmanās warning for @NoVA is worth taking into consideration.
I have never had that happen it blooms with the restā¦ Iām in zone 5b so things are different here.
If you were picking the tree for bloom time maybe you should pass on Toka, but if for black knot then not picking it would be a mistake. Sorry I edited my original post because it made little sense! Good info for sure. Itās nice to see the collective experience of all.
Drew, I lost the blossoms two years in a row so I have never have tasted it but it has the right characteristics, fast growing and big sharp spurs. I know the person who gave me the scions and have eaten the fruit at his place. There is a chance he got the scions mixed up but I think it is the real thing. Iāll know for sure this summer.
I rethought what I said, and in warmer zones I have heard of problems like this so I removed that statement. Their is no reason also to think it is not Toka. Even if it is wrong it still shows in zone 7 times can vary. Do you have Superior? That is another decent plum worth growing on itās own that has black knot resistance too. That could be a better choice but may be late to bloom too there?
And no matter what one chooses as rootstock (for the most part) you can make it work Shiro, Toka, whatever. I have a tree well many trees with multiple grafts. Satsuma worked well for me. I have Toka, Superior, and Vermont on it. I have Laroda, Lavina, Spring Satin, and Howard Miracle on Nadia.
I have pembina, superior, and black ice that havenāt opened yet. Emerald beauty was first, my pluots second, J plums in general third. It seems like the J plum American crosses bloom last with the exception of E plums, they are much later. I have never noticed but it may be true that bloom times are closer together in northern latitudes.
I have 8 pulots and all are going to be in full bloom within the next few days. My shiro, satsuma, santa rosa and Burbank are all noticeably behind but I suspect no more then 1 week given the temps.
I believe it has to do with chill hours, and not latitude. I am in W. WA, and my plums are not opening together.
P. americana flowered a week before Black Ice. Black Ice flowered with Krymsk-1, and two days before Shiro. Superior looks a couple days ahead of Alderman, but neither looks like they will bloom tomorrow, or the day after. My LaCrescent graft woke up, but no blooms yet. My Shiro is a day or two ahead of my neighborās Methley. Both are are in full sun, and near the sidewalk.
Thanks, Scott!
I will pass Santa Rosa. I think (and I hope) Shiro will be doing well here. My beauty plum is in ground for 3 years now, and I have not seen black knots. Not sure if it is black knot resistant.
I do see fungal problems on other fruit trees in my yards, such as figs, crabapples and asian pears, but I havenāt seen black knots.
Thank you mamuang!
In my yard, these plums bloom at quite different time. My beauty plum is in full bloom now.
Are your pluots at the same stage as my Beauty? Beauty is a very early bloomer.
