For some reports from zone 3 / 4 Canada. Not ONLY Euro plums but you can ignore the ones that don’t interest you.
http://forums.gardenweb.com/discussions/1888864/lets-talk-about-plum?n=716
It has gotten huge with tons of posts and photos so I summarized it as of march 7, 2017.
Opal
Hail damage made them not ripen properly I think but for what I tasted, concluded that I think Mt. Royal is still a better plum.
Here is a Opal info: Opal European Plum Midsummer. Wisconsin plum breeder Brian Smith noted that Opal is the hardiest European plum available. Bob Purvis reported it to be hardy to about –33°. Some years ago we sent 25 trees up to Alaska. Kevin Irvin, then vice president of the Alaska Pioneer Fruit Growers Association, arranged the order. He wrote to me, “This plum is hardy in Anchorage, AK, and ripens dependably every year.” One of the first Europeans to fruit in the season. Good quality, reddish-purple, medium-sized, round, semi-freestone. Firm yellow flesh. Medium-sized vigorous tree. Excellent cropper. Prunus domestica ZOullins x Early Favorite. Alnarp, Sweden, 1948. 3. ME Grown. (3-6’ bare-root trees). August? (Konrad – z3/4)
Here in Fairbanks that made last winter (which was really a non-winter by our standards), so we’ll see how it goes. (squarepegman z2/3)
Patterson’s Pride
great for pies & processing, [better storing too] not like most others like Pembina/Supreme too soft watery/runny! proves to be the best as cold hardy plum, I believe it’s a zone 2, with minus 7 degree this spring after flowering it still has hanging fruits, one of the best processing plums, firm, not soggy and semi freestone, the only drawback…a late ripening plum, some years it doesn’t quite make it, a unique weeping plum and tree keeps very low to the ground. champ of a plum when it comes to processing as a Asian Hybrid, totally freestone, not mushy. . ese are the only one’s I know of in the Asian hybrids which get better the longer they stay on, still firm and skin not very bitter, can eat them whole. Early to mid September. (Konrad – z3/4)
Pembina
(or Supreme) is still most reliable. Mount Royalis a better tasting plum. prone to split (Konrad – z3/4)
is similar to Supreme but cracks easy I found…got rid of my Pembina, flesh is sweet juicy (Konrad – z3/4)
Petite Sour de la Mont Royal
I am very happy with my Petite Sour de la Mont Royal also. It has been through 4 winters now with no dieback at all, even being in a less than ideal location with some north wind exposure and in a low place. It does have good prevailing west wind protection though. I agree with Konrad that it may be the hardiest European type plum. (katie77q)
Is a offspring of Mt. Royal from Hardy nursery in Quebec…and yes, possible hardier then Mt. Royal. tasted very similar to Mt. Royal. Late august early September. (Konrad – z3/4)
Pipestone
aphid magnets (Mattpf – z4)
just horrible in pollination, you’ll get the odd fruits at times but never loaded in my experience. (Konrad – z3/4)
Prunus Nigra B
B I added on because it was taken by Bernie near Winnipeg along the river growing wild and probably not diluted with other species. Best pollinator. (Konrad – z3/4)
Ptitsin #5
they fall down easily, pick most of them when they do and ripen in the house for about 3- 4 days…they don’t get soggy like most Asian plum/hybrid get, nice firm aromatic and free stone, a must have for tough growing condition! they seem to taste better after a couple of days in the house…the flavor! They don’t spoil easy like most other plums. Ptitsin is a good pollinator…the #5 which I have is one of the better ones, fragrant plum, free stone and stays firm many day’s. The only problem is, they fall off very easily, then I usually pick most and after about 2 or 3 days in the house they’re nice to eat. (Konrad – z3/4)
Ripeing early august 2016 (Mattpf – z4)
Sapalta cherry plum seedling 07-01
set some fruit even at around minus 7C at the orchard. This one is really sweet and I love the marbled flesh, anybody wants it I can give out bud wood but comes with a warning from the breeder…doesn’t pollinate easily and short shelf life, eat right off the tree it is very nice with 15 brix, Thean had 17 brix this year in the City. One huge plus…it’s’ free stone! I can eat the whole plum with skin when this sweet. Early august. I let a couple of Sapalta 07-01 ripen longer and just picked…was reading a whooping 19 brix! Early-mid august. prone to split (Konrad – z3/4)
Sinikka
http://suomalainentaimi.fi/luumu-sinikka-fine
prunus domestica from Finland seems to be hardier then Mt. Royal…will have allot more plums to pick then Mt. Royal in town, smaller but good. is similar to the blue Damson. a little smaller then Mt. Royal but hardier it seems and spring frost resistant, had no Mt. Royal on a separate tree right beside, good alternative to Mt. Royal I think for tougher growing condition…not as sweet but not bad either. Also Good for pies…semi freestone, 14 brix, about 2 weeks earlier then Mt. Royal. Mid august. (Konrad – z3/4)
Skiba
starting to drop, not bad…about a average plum…showed 12 brix, cling stone. Early-mid august. (Konrad – z3/4)
Sprouts sunshine plum
Clingstone. You have to keep them a while for them to get softer, then they are fairly good and more juicy! 14brix . Early-mid august. (Konrad – z3/4)
Startovaya
Russian. put on more than six feet of growth. They have terminal buds now; maybe they’ll survive. (Konrad – z3/4)
Supreme
(or Pembina) is still most reliable. year it does split also…I really don’t like it too much, [by the time you pick it and bring to the house she’s runny/soggy!!] This Supreme picked today and given away to neighbors …wife was saying, graft ALL Asian plums over to European prune plum…actually, one branch I put on already this spring, this branch will be cut off next spring. Mid August. (Konrad – z3/4)
Toka
what I tasted was very High quality. trust me you want waneta over toka. aphid magnets. probably are the best tasting I have. pretty good tasting plum it’s semi freestone and crunch makes it something I’m not really used to. they lasted about a week on the counter . Toka is the best tasting plum out of all I have here the taste is extreme flavour . I did my last pick of toka yesterday. Fruit are like big cherries and can be picked before they are soft and get better a few days sitting out. I’ve heard some people saying bad things about this plum on this forum . It’s one of the best tasting fruits .size and productivity might be an issue. Seems to be a super fast growing tree and a super long bloomer . One problem I had with them is they fall very premature and Calgary winds knocked off a lot so might be worth setting up something to catch fruit and prevent damage from hitting ground.
Mid august to early September. (Mattpf – z4)
Has intense nice flavour but I was disappointed with the small fruit, guess we don’t mind so much when compensated by taste. got a nice crunch to it, very solid, for some reason this year with taste, I wasn’t dancing up and down lol. I think too much rain made them different, last year it was better. Early to mid September. (Konrad – z3/4)
Waneta
is very hardy mine did so well I planted a second last year and grafted tons to everything because it’s so productive and a tad bit later than the rest. It’s rated one of the best will produce year after planting. It’s amazing. trust me you want waneta over toka. it amazes me. It grows more fruit than it does new branches only one year after planting and the tree it self is beautiful the fruit are big high quality fast yielding trees. Here in Calgary they grow like a charm. aphid magnets . clingstone good for fresh eating Mid august to mid september. (Mattpf – z4)
so far it’s a terrible aphid magnet. I pulled out all my Underwood, Lacresant, and Wanetas this fall as they were taking up space I could use for better fruit (Konrad – z3/4)
Underwood
I pulled out all my Underwood, Lacresant, and Wanetas this fall as they were taking up space I could use for better fruit average or below, cling stone …didn’t do a reading but was pretty spicy, not enough sugar, need a couple more years before I make a decision if I’ll be swinging the ax lol. Mid August. (Konrad – z3/4)
Valton
seems Asian hybrid, originated in Quebec, cling stone, fair tasting but this could be the wet season. [no splitting!] Early September. (Konrad – z3/4)
Bug Control
i used copper spray in winter and fall I probably will spray again in spring as we had a very wet last summer. It helps with black not and bacterial issues caused by moisture. I do use horticulture oils for aphids but realized water from the hose If properly done is just as effective or more because it doesn’t kill the good bugs. I will definitely use a dormant oil this spring after I spray copper. We had an aphid epidemic here last year this will help I hope . Besides that nothing special. Biggest challenge in southern Alberta is winds. You put a lot of effort into babying the trees onlybto come home to all your plums bruised on the ground. I used seven last year with horrific results. One week later the yard was covered in dead earthworms. I sprayed trees and rain washed it off few days later . After that the aphids got even worse about a month later. (Mattpf – z4)
So far I didn’t have to spray anything except last year for aphid problems on some young trees with rapid growth spurt… have used sevin, little soap and horticultural oil. (Konrad – z3/4)