Sempervivum and Jovibarba forum: What causes semps to flower?

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Name: Mark McDonough
Massachusetts (Zone 5a)
Region: Massachusetts Enjoys or suffers cold winters Garden Procrastinator Native Plants and Wildflowers Garden Photography Foliage Fan
Birds Seed Starter Hybridizer Sempervivums
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AntMan01
Jan 11, 2018 7:29 PM CST
I don't fertilize my semps, and I grow them in lean sandy soil. Some years they don't flower at all, while in other years they might bloom profusely. I'm not really interested in the flower per se, other than for hybridization. What encourages semps to flower, fertilizer, more abundant watering? Is it just age/maturity of rosettes?

S. heuffelii 'Gold Bug' in mid July 2013, nearly 50% of rosettes wereflowering. The next time it flowered was this past summer 2017, with 2 rosettes blooming. Most years no flowers.

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In most years my mature clump of 'Nouveau Pastel' does not flower, if it does flower there might be just 1 - 2 rosettes that flower. One year (2014) there were lots of flower stems. I'm very interested hybridizing with this one, unfortunately that year I was still working crazy hours and I missed the opportunity. View of a single flower stem with heuffelii 'Torrid Zone' and ciliosum ssp. ciliosum (sy. var. borisii) in the background.

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S. heuffelii 'Torrid Zone', a Bill Nixon hot one, in 2017 had one rosette that flowered. I hand pollinated nearly every flower on this stem (flowers were emasculated) with pollen from 'Gold Bug'. Mid July 2017, with bright red rosettes in view, and the tawny tan rosettes of 'Nouveau Pastel' in the background.

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S. ciliosum ssp. cilosum (got it many years ago under current synonym of var. borisii), it almost never flowers. This photo of a rare flowering moment in June 2001, nearly 17 years ago. I wish this one would flower more, as the flowers are very attractive, bright yellow, stems not too tall, and I would use it for hybridization. This particular planter had aged and was breaking up, so I moved it to a new dish-style planter, where it always looks great but has never flowered since. Three views: in flower June 2001. Same plant mid November 2001 when frozen. Plant in dish-style planter in May 2010 taking on a red flush of color.

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Final image, close-up of S. ciliosum ssp. cilosum (syn. var borisii) in mid June 2016, catching glimpse of red heuffelii 'Torrid Zone' and dark tan 'Nouveau Pastel' above.

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Avatar: Jovibarba x nixonii 'Jowan'
Allium 'Millenium' - 2018 Perennial Plant of the Year:
http://www.perennialplant.org/...
https://www.waltersgardens.com...
Name: Kevin Vaughn
Salem OR (Zone 8a)
JungleShadows
Jan 12, 2018 9:55 AM CST
Mark,

Combo of genotype and environment seem to be involved. Some species like the calcareums and atlanticum don't flower very often. Warm weather seems to increase the % of blooming rosettes. The very warm summer of '17 made virtually every cultivar have a bloomstalk. It was a goldmine for me in crossing all kinds of things together, with 236 different crosses.

Stress also plays a part. I had my first shipment from Fernwood stay in customs for a month. The plants were etiolated and several in that group went right into bloom. Luckily I only lost one cultivar because the smaller rosettes included didn't bloom. I was able to do some crosses with these stressed blooming plants although the seed set was low, at least I had the genes from that cultivar into my seedlings.

Kevin

Name: Mark McDonough
Massachusetts (Zone 5a)
Region: Massachusetts Enjoys or suffers cold winters Garden Procrastinator Native Plants and Wildflowers Garden Photography Foliage Fan
Birds Seed Starter Hybridizer Sempervivums
Image
AntMan01
Jan 12, 2018 5:36 PM CST
Thanks Kevin, the first two things make sense; that some don't flower as often as others, and warm weather can help induce flowering.

I hadn't thought about stress as being something to induce flowering. It leaves me wondering if one could create a stressed situation, such as keeping potted semps under a roof to keep them dry in spring, where they want to start growing but withhold watering until they become very dry and visibly stressed, then eventually resume watering where they will spring into strong hydration and catch-up growth. Might be worth an experiment.

Perhaps fertilizing in spring could induce more flowering too.
Avatar: Jovibarba x nixonii 'Jowan'
Allium 'Millenium' - 2018 Perennial Plant of the Year:
http://www.perennialplant.org/...
https://www.waltersgardens.com...
[Last edited by AntMan01 - Jan 12, 2018 5:36 PM (+)]
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