I'm no expert, but remember growing up with many plum trees on our acreage in Zone 3. They were delicious and sweet, smaller in size, red skinned, and about 1-1.5" in diameter. Some years we had lots of fruit, while others not so much. I too would love to see photos and hear about personal experiences, they are inspiring. It is impressive growing fruit in colder climates.

I planted a Brookgold plum last year (Spring 2016) that I bought from Calgary's Sunnyside Garden. I didn't see this forum, especially 'Let's talk about plum' post, after I bought the Brookgold. I read that people are having a tough time with brookgold setting fruits. I will see what happen these few years. I planted a Nanking Cherry 6 feet away for pollination.

Here is a photo of my ptitsen 5 pure Japanese plums beside two small yellow Japanese plums from okanagan and some small Manchuria apricots.As you can see these ptitsen 5 plums are tiny like the size of cherries

The ptitsen 5 plums were the first plums ready in my orchard they started to drop off the tree end of July early August. Need to let them ripen a bit on the counter before eating . This tree was very receptive to its neighbor 4feet away they both produced a lot of plums and both are pure Japanese plums.

Here is a photo of my red Japanese plum . They hang on the tree till mid August as a golden plum than within the last week before they fall off the tree they turn red. I would love help to id this plum it definitely is not a hybrid plum . I'm thinking it maybe one of the red plums from the ptitsen series these plums are excellent eating fresh and are medium size. They smell amazing flesh is juicy and not grainy or mushy skin is thin and not sour . This plum is excellent for eating would not do good for much else . Here is a photo of them about a week before ripening and turning fully red.

Here is my pure bred Japanese plum collection :)

now id love to see and hear everybody else's.

Paying attention to the blooming sequence can reveal an awful lot concerning if your red plum is Japanese (ie. prunus salicina) (old books, wild p. trifolia). If the plum likes to bloom a little later than ptitsen then you should suspect some ingression of the north american types. More information regarding prunus trifolia are through U of Sask, from Art
Coutts of Unity Saskatchewan , or those involved in the importation of this culture. The Coutts collection seem to scatter fruit on the ground the moment they are ripe.

I can see what your getting at but it's the green plum that falls all over the ground not the red. This green plum is ptitsen 5 from bylands. The other red was brookgold from bylands but they have seemingly used the wrong wood to propagate or nobody on this forum has ever fully ripened brookgold till its starting to turn red.

Pay attention in the flowering..if the red one flowers later then Ptitsin then it has more of the hybrid strain...think thats what alcan means. Normally Ptitsin flower very early...love the large fragrant flowers on the Ptisin!

The red one could be the Ptitsin #10...I grafted some, no fruit yet but I know they're on the red side. Looks like yours is the same as this Ptitsin shown here.

Check this out...

Ptitsin

Brook gold stays gold when ripe

I had grown the Ptitsin #5 for years but grafted over most of the tree... I used to say the Ptitsin #5 is the pits because I simply didn't know it's full potential for many years...plums would fall off and not quiet ripe....it took a long time to find out how to go about...pick most plums when they start to drop, take to the house and in 3 or 4 day's they would be really nice to eat, still firm flesh, free stone...not watery/soggy like you get in a day or two on most other hybrid plums like Pembina and Supreme. Supposedly these Salicina's are good pollinators for other hybrid plums.

I pay extremely close attention to these trees. Enough to notice the difference between Japanese and hybrid plum buds leafs and fruit from its visual features and fruit texture

The ptitsen bloomed at the exact same time as this plum did maybe a few days after but very similar bloom time hence the heavy loads of fruit the two produced as they are only 4ft away from each other. I assume it's a ptitsen 9 as it came from bylands and summer land budwood orchard near by sells ptitsen 9 I'm certain bylands buys bud wood from them

i do agree with you Konrad they look very similar to the ptitsen 10.