Hydrangea paniculata (panicled hydrangea) trial results 2021–2025
Objectives and purpose of the trial
Sweeps of hydrangeas lining the RHS Bridgewater beds in 2025
Rosy-tipped ‘Jane’ panicles packing colour into the trial beds
What is an RHS Recommended: Award of Garden Merit?
The RHS Recommended: Award of Garden Merit helps gardeners choose plants that are reliable and perform well in real gardens. Plants that receive the RHS Recommended: AGM have been thoroughly tested and shown to be:
- Easy to grow and reliable in normal garden conditions
- Readily available to buy in garden centres or online
- Healthy, robust plants with strong growth and appearance
- True to type, maintaining consistent shape, colour and form
- Reasonably resistant to common pests and diseases
Judging criteria
The following factors were all taken into consideration as part of the judging of the trial:
- Vigour
- Health
- Flower size, shape and colour
- Stem colour
- Habit
- Distinctiveness
Hydrangea paniculata – RHS Recommended: AGM winners
Hydrangea paniculata Living Little Passion ('Lc No13') (Living Creations Series)
Hydrangea paniculata Pinky-Winky ('Dvppinky'PBR)
panicled hydrangea [Pinky-Winky]
- 1–1.5 metres
- 1.5–2.5 metres
Hydrangea paniculata Living Colourful Cocktail ('Lc No15'PBR) (Living Creations Series)
panicled hydrangea [Living Colourful Cocktail]
- 0.5–1 metres
- 0.5–1 metres
Hydrangea paniculata Living Little Passion ('Lc No13') (Living Creations Series)
Hydrangea paniculata Pinky-Winky ('Dvppinky'PBR)
panicled hydrangea [Pinky-Winky]
- 1–1.5 metres
- 1.5–2.5 metres
Hydrangea paniculata Living Colourful Cocktail ('Lc No15'PBR) (Living Creations Series)
panicled hydrangea [Living Colourful Cocktail]
- 0.5–1 metres
- 0.5–1 metres
The longevity of the trial demonstrated what an excellent garden plant Hydrangea paniculata is. I was genuinely surprised at how long a flowering period you can achieve with this group of plants – from June right to the end of November.
Why the RHS Recommended: AGM was awarded
PINKACHU panicles blushing from white to rose
RHS Bridgewater hydrangeas at full summer peak in 2023
RHS Recommended: AGMs rescinded
Plants and location
What was planted?
Throughout the trial, the RHS Trials team recorded observations at regular intervals, maintaining consistent records to capture plant performance across the season. Data collected included photographic records, flower colour grading and intensity, flowerhead size, leaf and foliage size, taxonomy and plant habit, as well as the ratio of flowers to foliage. Flowering dates and duration, autumn colour and the appearance of flowers at early stages of development were also assessed to build a comprehensive picture of each cultivar’s ornamental value.
Where was it planted?
The young hydrangeas were planted directly into the open ground in the trial beds within The Old Frameyard at RHS Bridgewater, creating a structured display where differences in habit, flowering and garden performance could be easily appreciated. Here are some considerations for planting Hydrangea paniculata:
- Plant hydrangeas in spring or autumn, ideally in light shade. However, plant in a sunnier spot if the soil is not too dry in summer
- For Hydrangea paniculata, it doesn’t matter whether your soil is acidic or alkaline, as long as the ground is moist but well-drained
- Hydrangeas are hardy and flower on the current year’s growth
- Regular pruning is not essential, but annual pruning of last year’s growth in early spring encourages more prolific and larger flowers
Cultivation
Planting process
Preparation of the trial beds began in September 2020, when they were filled with loamy topsoil to provide a uniform growing environment across the site. Most entries were represented by three plants, allowing for side-by-side comparison, although a small number of entries included fewer plants.
Planting took place in mid-May 2021, with Beds 1 to 3 planted on 14 May and Beds 4 to 6 completed the following week. Each plant was positioned with care, spaced 1.2m apart, with 1.4m between entries along the length of the beds. This generous spacing allowed each plant to develop fully and ensured that differences in habit and performance could be clearly observed over time.
Following planting, a layer of strulch (straw-based mulch) was applied to help suppress weed growth and retain soil moisture. Around each plant, a small collar of bare soil was left to prevent the mulch from resting against the stems. Where planting gaps occurred, short bamboo canes were used to mark positions and maintain the structure of the trial layout.
Watering was carried out as required using a hose and lance with water from a borehole, allowing the approach to respond to changing conditions throughout the growing season. As the planting matured, a dripline irrigation system was installed during winter 2022 to 2023, providing a more consistent and efficient method of watering.
Pruning formed a key part of the cultivation approach. All plants were cut back hard in March 2022 to around 7.5cm above ground level, encouraging vigorous new growth and the production of multiple flowering stems. This approach was repeated in March 2023, once snow had cleared, cutting just above the previous year’s growth.
In 2024 and 2025, a more varied pruning regime was introduced to explore how different techniques influenced growth and flowering. Within each group of three plants, the front plant was pruned hard, the middle plant received a lighter reduction, and the rear plant was only lightly trimmed to remove old flower heads. This allowed different pruning approaches to be compared directly within the trial.
We got a tight, dense structure on plants pruned hard. They were cut back to two buds from the previous year, which created long extension growth and bigger but fewer flowers – it’s a good technique to keep plants small if space is limited.
How plant health was managed
Weather
Weather conditions had a strong influence on plant health throughout the five-year trial. Soon after planting in 2021, temperatures exceeded 35°C during a prolonged dry spell, placing early stress on newly established plants. This was followed by a mild, wet autumn and a gradual move into winter frosts.
In 2022, plants experienced intense summer heat approaching 40°C, followed by an unusually mild and wet late autumn. Temperatures then dropped abruptly to -8.5°C in December, without a period of gradual cooling, exposing plants to sudden cold stress.
Conditions in early 2023 remained unsettled, with further cold spells, snow and a brief cold snap before a milder spring. The growing season itself was mixed, with alternating rain and sunshine, followed by unseasonably warm weather in early autumn.
The pattern shifted again in 2024, which was dominated by storms, heavy rainfall and high winds, leading to some physical stem damage.
In 2025, prolonged rainfall early in the year caused waterlogging, before conditions turned markedly dry from mid-February onwards. Drought was declared in north-west England in late May, and a series of heatwaves through June and July added further stress despite intermittent storms.
Across the trial period, the combination of wet winters, dry summers and rapid shifts between extremes is likely to have placed the plants under sustained environmental stress.
Soil
Soil conditions were monitored annually from March 2021 onwards. The pH remained stable throughout the trial, ranging between 6.4 and 6.7, which was suitable for the plants grown.
From the outset, analysis showed consistently high levels of copper, zinc and iron, reflecting the origin of the site soil. These levels could not be readily altered and were considered a constant background factor across the trial.
Nutrient management evolved in response to annual results. In 2022, potassium deficiency was identified and corrected with an application of organic fertiliser. In 2023, a magnesium-rich fertiliser was introduced alongside additional organic feed. From 2024 to 2025, applications of organic and nitrogen fertilisers were continued and adjusted as the planting matured.
Despite this, some plants showed symptoms consistent with magnesium deficiency, particularly in the earlier years of assessment. As soil levels were considered adequate, this pointed to limitations in nutrient uptake rather than supply. Periods of winter waterlogging, combined with high levels of other elements, are likely to have contributed to this.
Challenges
Disease became a more significant factor in the later years of the trial. In autumn 2023, a wider outbreak of Phytophthora ramorum was recorded at RHS Bridgewater. Following this, three plants that died over the winter of 2023 to 2024 tested positive for the pathogen.
Further losses occurred over winter 2024 to 2025, with four additional plants affected. Initial testing again indicated Phytophthora ramorum, but subsequent analysis identified Phytopythium litorale, a closely related organism that can produce similar results despite being biologically distinct.
This introduced some uncertainty over the precise cause of earlier plant failure, as original material was no longer available for re-testing. However, it is likely that pathogen presence, combined with challenging growing conditions, contributed to plant losses during this period.
How to grow hygrangeas
Explore all the information you need to know to grow and care for hydrangeas in your garden
Discoveries
Hydrangea trail | 2025–onwards
The trial proved highly popular with visitors, leading staff to establish a dedicated route through the garden featuring 68 cultivars. Each cultivar, including the 12 awarded the RHS Recommended: Award of Garden Merit, is now available to view throughout the garden, creating a lasting legacy of the trial (map coming soon).
Plant movements | October–November 2025
Following the judges’ final meeting, plants were lifted in October and November 2025. One or two specimens from 10 cultivars were transferred to the National Collection of Hydrangea paniculata at Darley Park, Derby. Most of the remaining plants were replanted throughout RHS Bridgewater, although a small number were destroyed in accordance with the breeder’s instructions.
People’s Choice | July–September 2025
For the first time at RHS Bridgewater, visitors were invited to vote for their favourite entry. Voting took place between 30 July and 30 September 2025. While some operational challenges were identified and will inform improvements for future trials, the initiative was well received. Two entries tied for first place: Hydrangea paniculata ‘Phantom’ and Hydrangea paniculata LIVING LITTLE PASSION (‘Lc No18’) from the Living Creations Series. Third place went to Hydrangea paniculata LIVING COLOURFUL COCKTAIL (‘Lc No15’), also from the Living Creations Series.
Shadowing the judges | 2025
During the 2025 judging meetings, Dr Yan Wang, multi-award-winning artist and photographer and RHS Bridgewater Artist in Residence (2024 to 2026), shadowed the panel. She observed deliberations, conducted individual discussions with judges and photographed selected flowerheads. Her resulting exhibition, The Perfect Flower, will be on display in The Potting Sheds at RHS Garden Bridgewater from 24 April 2026 to 28 February 2027.
National Collection visit | August 2024 and 2025
The judging panel visited the National Collection of Hydrangea paniculata at Darley Park, Derby, in August 2024 and 2025 to assess more mature specimens of the trial entries. The drought conditions in 2025 resulted in generally more advanced flowering compared to 2024. The 2025 visit also included a tour of Bluebell Arboretum to view additional cultivated examples.
Early observations and plant health | July 2023
At the early stages of the trial, judges noted concerns about foliage condition in some entries. This was thought to indicate magnesium deficiency rather than heat stress, as symptoms were not uniform across all plants. Soil analysis suggested adequate magnesium levels, but uptake may have been affected by prolonged periods of waterlogging following very wet winters. Elevated levels of heavy metals in the soil may also have contributed to reduced nutrient absorption.
Who was involved?
Judges of the trial
The Hydrangea paniculata judges included Chris Sanders (Chair and RHS Woody Expert Group Member), Michael Hickson (RHS Woody Expert Group Member), Peter Jones (Director of Horticulture, Eden Project), John Massey (Nurseryman, Ashwood Nurseries), Kevin Pratt (Horticulturist and garden speaker), Joanne Ryan (Living Collections Team, National Trust), Peter Smith (National Collection Custodian, Darley Park), Rachel Vernon (Bluebell Arboretum & Nursery), Robert Vernon (Snr) (Bluebell Arboretum & Nursery) and David Wheeler (Editor, Hortus).
Suppliers to the trial
List of plants in the trial
Peter Jones’ must-see stops on the hydrangea trail
Hydrangea paniculata Pinkachu ('Smhppinka'PBR)
panicled hydrangea [Pinkachu]
- 0.5–1 metres
- 1–1.5 metres
Hydrangea paniculata Living Colourful Cocktail ('Lc No15'PBR) (Living Creations Series)
panicled hydrangea [Living Colourful Cocktail]
- 0.5–1 metres
- 0.5–1 metres
Hydrangea paniculata 'Jane'PBR
panicled hydrangea 'Jane'
- 1–1.5 metres
- 1–1.5 metres
Hydrangea paniculata Pinkachu ('Smhppinka'PBR)
panicled hydrangea [Pinkachu]
- 0.5–1 metres
- 1–1.5 metres
Hydrangea paniculata Living Colourful Cocktail ('Lc No15'PBR) (Living Creations Series)
panicled hydrangea [Living Colourful Cocktail]
- 0.5–1 metres
- 0.5–1 metres
Hydrangea paniculata 'Jane'PBR
panicled hydrangea 'Jane'
- 1–1.5 metres
- 1–1.5 metres
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