Aeonium (tree houseleek) trial results 2022–2024
Objectives and purpose of the trial
Sculptural aeoniums steal the show at RHS Wisley in August 2024
Aeoniums thrive by the sea at The Minack Theatre in June 2025
What is an RHS Award of Garden Merit?
The AGM is intended to help gardeners choose plants that are likely to perform in their gardens, and is only awarded to plants that are:
- Excellent for ordinary use in appropriate conditions
- Available
- Good constitution
- Essentially stable in form and colour
- Reasonably resistant to pests and diseases
Judging criteria
The following factors were all taken into consideration as part of the judging of the trial:
- Habit
- Foliage quality, form and colour range
- Overall appearance and impact
- Pest and weather resistance
- Flower – where relevant
Aeonium AGM winners
Aeonium arboreum 'Variegatum' (v)
houseleek tree 'Variegatum'
- 0.5–1 metres
- 0.5–1 metres
Aeonium arboreum 'Variegatum' (v)
houseleek tree 'Variegatum'
- 0.5–1 metres
- 0.5–1 metres
I’ve enjoyed seeing how much the aeoniums have grown on from getting them in 9cm pots in 2022, to the fabulous specimens they are in 2024. It goes to show that these plants really perform when they are happy.
Why the AGM was awarded
Judges check in on aeoniums at RHS Wisley October 2023
Judges among aeoniums at The Minack Theatre in October 2023
AGM Rescinded
Plants and location
What was planted?
Where was it planted?
The young, rooted Aeonium plants were grown in containers in the Trials Garden at RHS Wisley, while concurrently at The Minack Theatre, entries were landscaped directly into the ground (borders). Each location presented its own set of growing conditions. Here are some key considerations for planting out aeoniums:
- As long as you bring them in before the first frosts, Aeonium can be grown in outdoor pots with well-draining soil
- Many Aeonoum species become semi-dormant during very hot summers, but their foliage will not wither if plants are grown outside in light shade
- Avoid overwatering in hot summers when the plant may be dormant
- Don’t be put off if the mother plant dies after flowering. Look closely and you will see she has produced several new plants first
Cultivation
Planting process
Cultivation at RHS Wisley
Aeonium entries arrived at RHS Wisley in March 2022 as 9cm rooted plants from Surreal Succulents Nursery in Cornwall (additional entries were received from Ottershaw Cacti and Penberth Plants). They were grown on in the Propagation facility for 15 months and gradually potted up into 3L containers.
In June 2023, the plants were placed outdoors in the Trials Garden. Each 3L pot was plunged into gravel within 30cm terracotta containers. To reflect typical home gardening conditions, no shade was provided, and plants were watered moderately through summer as needed. Those that entered dormancy received no watering.
On 6 October 2023, the plants were returned to the Propagation facility for overwintering. At this stage, they were removed from the gravel plunge and potted directly into the terracotta pots using a 1:5 grit-to-compost mix, finished with a gravel top-dress.
On 3 June 2024, after the risk of frost had passed, the aeoniums were moved back outside to the Trials Garden to continue assessment – this time in 5L terracotta pots.
Cultivation at The Minack Theatre
In April 2023, Aeonium trial entries were planted directly into a prepared bed/border at The Minack Theatre, situated at the side of the theatre, overlooking the sea. Most were planted from 1L containers, though the plants varied in their stage of development at the time.
Throughout summer 2023, nearly all entries showed vigorous growth – clearly benefitting from being planted straight into the ground. While there was some variation in size at planting, growth appeared more consistent across the different entries by the 2024 season.
The first full-forum meeting for the Aeonium trial at The Minack took place in mid-October 2023, following an earlier local forum meeting held in May. A further assessment by the local forum was carried out in May 2024 to evaluate how well the plants had overwintered.
How plant health was managed
Challenges and weather at RHS Wisley
All Aeonium entries at RHS Wisley were treated preventatively to guard against aphid activity. During periods of autumn growth, plants were watered twice weekly and given a liquid feed every six weeks at a rate of 15ml (1 cap) per litre, using the standard houseplant dilution.
Most plants were overwintered at a stable 6°C. However, a small number of more cold-sensitive entries were kept slightly warmer, at 10°C, to avoid cold stress. Plants that entered dormancy during the summer were not watered to reduce the risk of rot.
Challenges and weather at The Minack Theatre
Aeonium health was closely monitored during seasonal assessments, with particular focus on how well the plants tolerated environmental stress. A key focus was on how the plants coped through the exceptionally wet and windy winter and spring of 2024, which included torrential rain and multiple storms between January and March 2024.
These ongoing evaluations highlighted differences in plant resilience and helped inform future recommendations for preventative care and variety selection.
How to grow succulents
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Discoveries
2023 | Hardiest of them all
The hardiest cultivar featured in the trial was the multi-branched Aeonium spathulatum, which originates from the colder, mountainous island of La Gomera and the chillier regions of La Palma. This Aeonium is typically hardy down to -7°C and could potentially have overwintered outdoors in the UK. However, it was ultimately decided to bring all RHS Wisley entries indoors.
Who was involved?
Judges of the trial
The 2022–2024 Aeonium judges included: Claire Batten (Owner, Penberth Plants and RHS Tender Ornamental Expert Group member), David Ford (Vice-Chair, RHS Tender Ornamental Expert Group), Anne Clifford (Plant Heritage National Collection Coordinator), David Creese (RHS Tender Ornamental Expert Group member), Daniel Jackson (Owner, Ottershaw Cacti and RHS Tender Ornamental Expert Group member), Mellie Lewis (Author and National Collection Holder of Aeonium), Dean Lockwood (Former Head Gardener, Leeds Parks and Countryside), Daniel Michael (Owner, Surreal Succulents), and Jeff Rowe (Owner, Penberth Plants).
Photography: Plant and judges portraits provided by Nicola Stocken.
Suppliers to the trial
List of plants in the trial
Handy tools and information
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Get in touch
For more information on our RHS Plant Trials or to access older trial reports, please get in touch with our team via email at [email protected].
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