Succulent Hybridising and The Origin of x Semponiums
How and why Surreal Succulents bred x Semponiums
Since founding Surreal Succulents, Daniel Michael has created several Aeonium hybrids that are grown around the world, such as Aeonium 'Phoenix Flame', Aeonium 'Emerald Flame', Aeonium 'Blood', Aeonium 'Cornish Rose' and Aeonium 'Pomegranate'.
Daniel already had many years of hybridising experience, and he had often talked to RHS botanists about the theoretical chances of crossing other members of the Crassulaceae family.
Some of these, such as 'Phoenix Flame', have survived frost in testing, but most Aeoniums are tender and need protection over winter in the UK. So we started looking at how we could create plants with the architectural structure of Aeoniums and some of the hardiness of other succulents, such as Sempervivums.
What are x Semponiums?
x Semponium is an inter-generic hybrid between Sempervivum and Aeonium. The cross is possible because the two are genetically similar, both being members of the Crassulaceae family.
Sempervivums are generally small, compact plants. They are extremely hardy and can withstand temperatures as low as -20°C.
Aeoniums tend to be much larger and are mostly frost tender. Only a few species and hybrids can take frost.
Sempervivum
'Green Ice'
X
Aeonium
'Ice Warrior'
=
x Semponium
'Sienna'
x Semponium
'Destiny'
x Semponium
'Diamond'
x Semponium
'Mrs Frosty'
x Semponium
'Halo'
x Semponium
'Vortex'
How was this possible?
Sempervivum 'Green Ice' flower
We used two plants to create these inter-generic hybrids, which sounds simple enough. The difficulty is timing. Aeoniums bloom in early spring and Sempervivums in mid-summer, so the two almost never flower at the same time.
Aeonium 'Ice Warrior' flower
At the nursery we had a late-flowering Aeonium 'Ice Warrior', which we moved to a cool, shaded spot to slow its flowering and keep it going for what could be a once-in-a-generation cross. We chose Sempervivum 'Green Ice' because it is a strong Sempervivum cultivar.
The breeding process
In our breeding, we have found that using hybrid parents, rather than two species, gives a larger gene pool and many more possible outcomes.
Think of it like a family tree: seedlings from two hybrids have four or more original species parents behind them, rather than just two.
Crossing two hybrids widened the genetic mix and the potential for random traits, which gave us the best chance of an x Semponium showing up.
Ripe Sempervivum 'Green Ice' seeds fertilised with Aeonium 'Ice Warrior' pollen
The cross was by no means easy to pull off. We had to isolate the chosen plants to stop other pollinators contaminating them. We covered the flowers with fleece bags, cut off all other Aeonium and Sempervivum flowers, and moved the two plants into quarantine to keep the risk as low as possible.
Because the goal was hardiness, we decided the Sempervivum would be the seed-bearing plant. Our theory was that this would pass on as much of the Sempervivum's hardiness as possible, and that it would let us clearly identify whether we had hybrid seed.
Aeonium 'Ice Warrior' had plenty of strong, healthy pollen, and it has a very long flowering period, sometimes up to ten weeks.
Sempervivum 'Green Ice' produces a short flower spike with up to twenty flowers, which last only three to four weeks.
5-day-old x Semponiums
In the summer, Daniel took fresh pollen from the Aeonium 'Ice Warrior' and carefully transferred it to the newly opened flowers of Sempervivum 'Green Ice' with a soft paintbrush and tweezers.
He then left the flower to ripen in a dry, sunny spot for eight weeks, before collecting the flower heads and leaving them to dry out completely in a brown paper bag in a cool, dry place for a further two weeks.
Next we separated the fine, dust-like seed from the chaff, packed it into a cellophane envelope, labelled it clearly and stored it in the fridge for two more weeks until sowing.
In late autumn, a total of fourteen weeks later, Daniel spread the fine seed evenly over the surface of a tray of sterilised seed compost. He covered it with fine sand and carefully soaked the tray in a bath of sterilised water, then laid a thin piece of glass over the top to trap in humidity and help germination. The tray went into a bright spot, and we waited.
Daniel eagerly checked the seed every week, hoping to see signs of germination.
By week three we could see that the seed had germinated, but it was still too early to tell whether the cross had worked.
Two to three months later, to our excitement, the seedlings began to vary. Some were red, some tall and Aeonium-like, and at that point we knew we had done it: these were the world's first official x Semponiums.
Once the seedlings were big enough, we potted on every single one and gave each one star treatment, because we didn't want to miss any promising plants.
Over the growing season we picked out interesting forms and colours to grow on. This was hard, as there were so many good-looking variations.
We ended up choosing six varieties. Each one stood out for its form, colour or vigour, and no two looked alike.
Growing x Semponiums
x Semponiums grow very quickly, with strong hybrid vigour. Their leaves look fresh and clean all year round, and they seem to have a shorter dormancy than their Aeonium parents.
Hardiness was the main trait we wanted in these new hybrids: we were after a garden-proof, Aeonium-like plant for every region of the UK. Unfortunately, the hardiness of the Sempervivum mother did not carry over. x Semponiums are as tender as Aeonium 'Ice Warrior', which is known to only just survive -4°C. We were very disappointed, because it would have been a real breakthrough in hybridising.
Daniel and the rest of the Surreal Succulents team are still trying to breed hardiness into Aeonium, one hybrid at a time. Our goal is a range of winter-hardy plants that everyone can enjoy without worrying about losing them.
RHS awards
The x Semponiums had attracted a lot of interest, and we decided to show them for the first time at the RHS Chelsea Flower Show 2020. That show was cancelled because of the pandemic, so we kept them out of the public eye until it returned in September 2021.
x Semponium 'Sienna' was part of our 2021 show garden, which won a Gold Medal. We entered 'Sienna' into the Plant of the Year competition, and it came third in the RHS Chelsea Flower Show Plant of the Year 2021.
At the next Chelsea Flower Show, in 2022, we revealed x Semponiums 'Diamond' and 'Destiny'. We entered both into Plant of the Year as well, and to our surprise, 'Destiny' won 1st place!
We could not believe it! It was truly a Surreal experience.
The future for x Semponiums
Now that we know how it is done, we are always trying new crosses for x Semponiums.
The next addition to our x Semponium range was x Semponium 'Darwin', released in April 2025. It comes from a completely different cross to the original 6 plants, which were Sempervivum 'Green Ice' x Aeonium 'Ice Warrior'. 'Darwin' is Sempervivum 'Pink Puff' x Aeonium nobile.
'Darwin' has deep red colouring and huge, chunky leaves, a combination of its two parent plants.
This seed batch was less successful than the first x Semponium series. 'Darwin' was the only seedling that stood out, and the others showed no resemblance to the Aeonium parent.
We look forward to creating more x Semponiums, and we are carrying on with our aim of breeding extreme hardiness into the Aeonium gene pool.
Thank you for reading!
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