Do you have 'Noella Nabonnand'? Because her color is similar to this, and she blooms early.

As for your question, I don't know. My general impression is that deciduous roses, one that regularly shed their leaves in fall (not just as the result of a freeze) stick to a schedule regardless of weather. Repeat-flowering roses that want to be evergreen bloom when conditions allow. I've seen wide swings in the dates of first blooms of my Teas and Chinas. Even if your variety responds to manipulation, I think it would be hard to do, but you may be more ingenious than I.

In my garden mid-May to mid-June is roughly the season of bloom of my European-origin once-flowering roses: Gallicas, Albas, etc. Centifolias are lateish, and some of the ramblers come in later June, and possibly into July. May is the big season for Teas and Chinas (Noisettes are variable, possibly influenced by their musk ancestry), but they can bloom earlier and later than that if conditions are favorable.

I'm not sure you can really force an early bloom. It's so dependent on weather conditions in the spring and some roses just like it warmer for a longer period before they start. Around here main bloom is the beginning of June and I had a Snowfire that NEVER bloomed until mid July. It liked it HOT before it would even think about putting on blooms.

Thanks, both ladies. First, I'll address Melissa's comment. RZ is not an old rose; it's quite modern. It's parentage is not posted on HMF https://www.helpmefind.com/gardening/l.php?l=2.63462.1&tab=36&qn=1&qc=0 In my garden it is much more genuinely purple than is Noella,so, though Noella seems great (mine is very young), it is just not the same colour class; RZ is much closer to the Purple Eden colour, and pinks-out much less in heat than does Purple Skyliner does. I have a general impression that most of my roses don't necessarily shed their leaves in fall-I will pay more attention to this factor this year, thanks to your comment. I have the impression that 2 teas of mine.(supposedly Souv d'un Ami and Archiduc Josef,but they look axactly alike to me),growing in a very sheltered spot) begin blooming very early, though not as a "flush" ,and don't lose their leaves.Clbg.Old Blush, though a darling to my heart, keeps it's leavers all winter, blooms early, then looks wretched for a while, dropping all it's leaves from powdery mildew/bs as the flush ends, and then they grow back,and it re-flowers...( I hope to figure out a way to get around this rose's period of ghastlyness; I love it too much to discard it) So the bottom line is that i might try to understand better the effects of dormancy on roses, and how it might condition bloom period.

Seil,thank you for your comment- our climates are so different, but there is much to be learned from people who are coming from different places.Yeah..."just like it warmer before they start"...maybe winter protection really would be worth a try. For example, wrapping up one of my RZ's in that white synthetic winter-protection cloth that people around here use on their border-line-hardy plants...it wouldn't cost that much, trying it on one rose...

Here's a link to an article fron Fine Gardening,I think by Paul Zimmerman. It doesn't deal exactly with the issue that interests me, but ...

O, those crazy Romans,lol! It sounds like it really might be interesting to try winter-protecting one of my RZs,say, with that white porus synthetic cloth ("tessuto non-tessuto it's called here) that people use during winter to protect their tender out-door plants. Maybe remove the leaves, too, by hand,to induce some degree of dormancy. I really do have to pay more attention to when different varieties "doze off a bit" during winter-I don't think any of my roses go truly dormant. The general impression is that they hold onto their leaves usually until more or less the end of December or even january,and by february are starting up again. Clbg Old Blush only very, very rarely loses it's leaves during winter-i think it's "dormancy" occurs after blooming-it gets all powdery-mildewed and bspotty,drops all it's leaves...and then starts re-growing. I love it too much to get rid of it: plan to grow a clematis montana into it, to cover for it during it's ghastly phase.

At the famous Chelsea Flower Show, where the big rose companies have massive displays, all of the roses you see are flowering a good month ahead of their natural schedule. They accomplish that by growing them in pots and putting them in a warm greenhouse. So anything you could do to increase temperature should hasten your bloom. Of course that could be a challenge in an open garden. But might you consider moving it to, say, a sunny south-facing wall, or some other such microclimate that is inherently warmer in spring than the rest of your garden?

In my garden the warm climate evergreen roses hold their leaves through the winter, then in March they lose them and grow a new set. In that month they look tatty. Once the new leaves are on they make new growth and set buds. This schedule may vary according to the weather: I'm not sure.

This thing about "when in rose season does a given variety start to bloom" is a big deal for me. As I've mentioned before, I don't much care for roses that open very late,because of the bad summer weather. Another reason is that, with so many roses, I don't really dead-head,so after the main flush is over, the whole garden tends to have a pretty tatty,messy appearence, so the late blooms can make me feel guilty that I don't give them a nice setting. But then there's this other thing about orchestrating garden areas to obtain certain colour harmonies. Right now, I have this kind of luscious little bouquet of Burgundy Iceberg, Mme. Ligier, and Azubis : burgundy, violet-pink, and lavender-I just LOVE it. So I'd love it if I could get this one particular plant of Rosengarten Z, in this one particular spot, to bloom earlier, because it is that special,rare dark purple,maintaining the colour in heat pretty well. Also, being a climber,it's vigorous enough to be pretty easy in my tough conditions-I just recently have started with floribundas, for example,and am finding that many of them are harder to get going,and don't really accept being watered only in their first year.

It's funny, because if you look on the Lens Roses site http://www.lens-roses.be/en_US/shop/page/13?ecom_main_cat=4&ecom_cat=25&ppg=12 ,you'll see that they offer both Rosengarten Z and Roville,but they say that RZ blooms from June-October,whereas Roville blooms July-Oct.Instead, in my garden, Roville starts early, in main rose season..(.and,I might add is still going strong and looking great now in mid-July!!! What a rose! This is the first year it's done this; previously I never thought that much of it) Instead, Super Dorothy starts late as they say it does on the site, as does Super Excelsa, though this latter is a little earlier than SD.

I wonder if removing the leaves would force an earlier dormancy and then the next flush could be timed. I have no idea, just a thought. I know some folks in CA do this, but I don't know if it's and aesthetic choice or practical one.

vaporvac, removing leaves does cause a kind of dormancy. We had a guest speaker talk about removing leaves from roses at one of our rose society meetings. Here in Florida we do have a REAL dormancy... so when we cut back in Feb. we were told to pull leaves off the bush.

Yes, in fact I was thinking of doing that, too. Another idea of mine-I think I'm going to start de-budding it now (it's still in bloom),and keep on removing any eventual buds. Then, maybe defoliate it in October/november,and wintwer-protect it when i start seeing people doing so with their tender "balcony2-type, potted plants It's worth a try...

What will the disbudding do?

O, just an idea, Vaporvac,part of the whole "thing" about sort of confusing the plant. RZ is still in bloom now, and does produce one or two flowers VERY early in the season-I wonder if, in a climate like Jackie's, it would behave as she describes her Emera? Just part of the experiment...

Gotcha. :-)