I assume that most people are breeding with this rose for reblooming climbers for northern climates. I am taking a slightly different route but still using Rosa multiflora for height.
I decided to first use Ames#5 crossed on Hansa (the tallest rebloomer I have often 2m) I did about 100 crosses. Got two hips with one seed each. Both germinated but were weak so they were much neglected. But once I got them in the ground I was glad I kept them. Both 30 cm of growth and snug to the ground. I know that I will need further cross to get rebloom but hope is there. Ames#5 is a multiflora/blanda cross and it gives me much hope.
My big mistake was killing off a cross on a hybrid that is prone to black spot ((Rosa rugosa alba x R woodsii)X Martin Frobisher). I did a lot of flowers with R. multiflora. I has at least 100 seeds but threw them out because of the BS. If only I was accepting of a fault I could have had a few seedlings that were resistant. I plan to repeat that cross. The female is a rebloomer.
It will be 10 more yrs with crosses to recover the rebloom but hey most things take time…
Ames 5 was a wonderful species hybrid developed, a combination of cold hardiness and floriferousness. It was developed 84 years ago (1932) and unfortunately (if I recall correctly) no progress was made with it to develop newer types of shrub roses. Perhaps a cold hardier type of Hybrid Musk could have been developed, which certainly would have been very attractive in the landscape.
I have thought it might be productive to make this cross again but using a cold hardier Rosa blanda (woodsii). However, as one avenue to pursue to develop cold hardy (Zone 3) Climbers, I now lean to developing a Rosa maximowicziana x Rosa woodsii species hybrid. Rosa maximowicziana has a prostrate growth habit but is cold hardier (it’s cold hardy to Zone 4 but can also survive quite nicely in Zone 3) than Rosa multiflora. But I wouldn’t stop there. I think it’s necessary to inject disease resistance, and the best potential for that is likely from Rosa wichurana. So a Rosa wichurana x R. woodsii hybrid would have to be developed to maintain relatively good cold hardiness and then combined with the Rosa maximowicziana x R. woodsii hybrid. Rosa wichurana, of course, also has a prostrate growth habit. Note: All three of these species are diploids.
A long term project for sure, but I think it’s an interesting one to pursue, which I’m doing. I made a few Rosa wichurana x R. woodsii crosses last year.
I got R. maximowicziana from Rosenposten, Denmark a few years ago. It really seems to be much hardier that the bulk rootstock multiflora or any multiflora hybrid I have tried. Those normally freeze to snowline here. R. maxi has very bristly and pliable stems. Last summe had first decent bloom and I was able to pollinate a few dozen flowers. I got a fair amount of seeds from the cross R. maxi x Applejack. I’m not after repeat bloom but any true rambler that would be cane hardy here. Currently Polstjarnan is the only one.
‘Postjarnen’ was orginated by Jarl Wasastjerna (1896-19720), a University of Helsinki physics professor and industrialist.
I’ll bet it’s a good chance he collected seed of Rosa beggeriana from this university’s botanical garden. However if this is true, we don’t know if the shrub was labelled correctly. Interestingly, It has been reported there are double flowered (likely semi-double) forms of this species.
If records exist, it would be interesting to find out what rose species and cultivars were growing in this botanical garden in the 1930’s (‘Postjarnan’ was introduced in 1937). If a list exists, and if the flower of this Rosa beggeriana that produced this seedling was pollinated by another species or cultivar, we might be able to determine what the other parent was. Or determine that the flower was likely self-pollinated.
The mystery is how did the combination of the shrub’s superb cold hardiness (Zone3) and its lanky canes that can be trained to be a Climber come about. It is the world’s most unusual rose in this respect.
There you go Jukka, some detective work for you to do. And we will expect a full report from your findings!
From encouragement from a friend I mass pollinated Postjarnan with polyantha pollen this past spring. I have basically given up on using Polstjarnan. It’s pollen didn’t look very fertile under the microscope and there has been almost no op hips from all the blooms it produced over the years. THe couple hips it produced had just one seed in each and they didn’t germinate. I dabbed polyantha pollen on lots of open blooms one day last spring. Come August there were 30 small hips and 77 seeds!!! So far there are 33 seedlings that have germinated!!! Out of the very first ones, there are some that died I think due to genetic abnormalities, but others are growing normally. It’ll be fun in a few weeks to see if some set flower buds to see if maybe Polstjarnan may be heterozygous for the major repeat bloom gene and get a clue if its male parent was likely a repeat flowering cultivar in that botanical garden. I absolutely LOVE Polstjarnan for its hardiness and vigor here in the Twin Cities and can’t think of a more reliably hardy rambler for us either. It’ll be fun to get some more ramblers or repeat blooming bush roses with a nice dose of winter hardiness from Polstjarnan.
With this very encouraging result, I think I would try some new crosses next summer with ‘Polstjärnan’. Because I already have obtained 10 seeds from 4 flowers pollinated with pollen of ‘Prairie Peace’ in 2014 but without germination. And in 2015, I have tried again with pollen of ‘Ames Climber’ on 15 flowers with poor result also, only 6 fruits with 26 seeds and no germination. And nothing was made in 2016. But maybe this year I will be lucky!? As Margit, I am waiting for to hearing if you get any juvenile bloomers.
I have found a «possible father» for ‘Polstjärnan’ on Finnish web site Simolanrosario.com (link below); ‘Gruss an Zabern’, a R. multiflora hybrid (or Lambertiana) obtained by Peter Lambert in 1904. I am just an amateur hybridizer but when I see the photos and with the description on Helmefind (link below) I see a family resemblance. What do you think about this possibility that ‘Polstjärnan’ is a cross between Rosa beggeriana and ‘Gruss an Zabern’?
I don’t know if this helped the seeds germinate, but I treated them like I do polyantha seed. I stratified them a little bit warmer at 10C instead of 4C. I like to stratify in peat. When some started germinating I brought the bag home and potted those up and then checked the bag periodically and pot up more that germinate. At home the temp in the basement is about 60F.
The Polstjarnan x polyantha seedlings seem to all be one time bloomers. Likely the other parent of Polstjarnan was a one time blooming rose versus a repeating rose. Some of the seedlings seem to have thornless stems!! I have thornless stems in some of my polys and it seems to be a simple recessive. I wonder if the other parent of Polstjarnan was some multiflora rambler hybrid that was thornless or a carrier for thornlessness (thornless stems but not underneath the leaves). Many of the seedlings are kind of weak, but thankfully about a third seem vigorous enough to survive. In the same flats with polyantha x polyantha crosses those are much more uniform and vigorous compared to the quite variable Polstjarnan seedlings. Hopefully some of these vigorous Polstjarnan seedlings will have pretty good fertility and produce nice seedlings.
Thank you Margit for asking. I’m excited for them to bloom next year. I was hoping there’d be a little blooming this past spring, but they must have been too small. They overwintered perfectly for our relatively harsh winter, which was promising. Most all of them had a lot of leaf spot or black spot or something and lost quite a bit of foliage. Hopefully crossing them to with some of the healthier polys again would help. Polstjarnan seems pretty healthy to me, so I was sad to see the seedlings being more disease prone than the parents. There is a huge Above and Beyond next to the Polstjarnan plant used and one of the seedlings sure looks like a hybrid with it with how robust and large the foliage is and aspects of foliage shape and prickles. It’ll be fun to see what the flowers will be like. That one is as tall as me now with some canes (~6’). The ones with poly dads are much more lax and arching over and across the ground a bit more.
Good luck as making a slightly more garden worthy cold zone clmber or rambler (Z2 3) that hits 12 feet plus is something that will be ground breaking … for now the small white blooms will have to suffice in my garden … as well as R. Paulii
Well I had some success with one of my cross of (HansaxAmes#5). The strong seedling is covered with flowers that are med-pink and single, they also carry the scent of multiflora. By fall I was collecting 20 seeds per hip. I saved the best 150 and will germinate those. I can only hope that I can recover the repeat blooms, scent, and height. I like using bridge species. Johannes [attachment=0]image.jpg[/attachment]
Would there be any merit to working with some of your setigera seedlings in lieu of polyanthas, David? Or do they create more health concerns? I don’t know if HMF’s hardiness ratings are accurate, but setigera is purported rated as good to zn 3b, as well as having a little color to it, and multiflora is 4b per that site. I also wonder if resistance to RRD might be better going that route?
I don’t have experience with seedlings yet, but have made a couple crosses on R. set. serena in the past, and am hopeful that the plant will have some merit. (I also like what you explained to me about the panicle arrangements of setigera descendants.) I have generally avoided multiflora, in part due to concerns about our alkaline soil.