a russian hybrid plum that seems to root vigorously from softwood

a russian hybrid plum that seems to root vigorously from softwood, podorak st. petersburg. This one survived -40C last winter, which was a happy surprise, and was worthwhile testing its rooting potential because of its parentage. The cultivar isn't well known on the Canadian prairies, so it's a fun addition to our nursery - an important focus for me has been developing methods to produce own root plum trees, trialing different cultivars and just keeping notes about what's worked. Feels like a small discovery, maybe someone else is doing this but very little comes up in my own research. Will they grow into large healthy trees? depends on the follow up care this year, plums can suffer from too much vigour the first season they root, so I've been experimenting with water, fertilizer, medium and winter storage - early success with Toka has me encouraged. This set of initial plants with stay at the nusery, and if all goes well I'll offer some next year. I still need to sort out how well it fruits here, we regularly have a dozen nights that reach -35C and some that can drop to -42C so that's my filter for zone 3 hardiness everything fruiting here has to pass through.