Shrubby Veronica trial results 2021–2023
Objectives and purpose of the trial
Shrubby Veronica trial in the Trials Garden at RHS Wisley
Trial bed at RHS Harlow Carr planted with shrubby Veronica
What is an RHS Award of Garden Merit?
The RHS Award of Garden Merit (AGM) is intended to help gardeners choose plants that are likely to perform well, and is only awarded to plants that are:
- Excellent for ordinary use in appropriate conditions
- Available
- Of 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:
- Plant habit and vigour
- Foliage colour in winter and other seasons
- Flower colour and coverage
- Flowering period and length
- Impact of pest and disease
- Plant consistency year to year and south to north
Shrubby Veronica (formerly Hebe) AGM winners
Veronica salicifolia 'Adel White'
- 0.5–1 metres
- 0.5–1 metres
Veronica salicifolia 'Adel White'
- 0.5–1 metres
- 0.5–1 metres
Overall I was struck by the continued diversity of leaf and flower of the Veronica genus. The number of varieties that had foliage that changed significantly in colour through the season was more apparent when they were all together.
Why the AGM was awarded
Forum assessment of shrubby Veronica trial at RHS Wisley
Shrubby Veronica trial assessment at RHS Harlow Carr
AGMs rescinded
Plants and location
What was planted?
Where it was planted?
This was a dual site trial, planted at RHS Wisley in the Trials Garden and at RHS Harlow Carr in the Sun Border. The trial was planted out in March 2021. Here are some considerations for planting out the shrubby veronicas:
- Shrubby veronicas need lots of sun and well-drained soil. They won’t survive well in shady, damp or extremely cold conditions
- The hardiness and size of hebes varies a lot, check plant labels or descriptions to find a plant that suits your location
- Most shrubby veronicas produce masses of pollinator-attracting flowers in the summer
- Many compact shrubby veronicas also grow well in containers in peat-free compost that drains well. Move containers to a sheltered spot over winter, so they aren’t exposed to really harsh weather
- Clipping plants after flowering can help to keep plants tidy
Cultivation
Planting process
At RHS Wisley, soil analysis indicated good levels of nutrients in Trials Garden beds. The beds were mulched with medium bark chip and drip irrigation lines were laid for watering in dry spells.
At RHS Harlow Carr the Sun Border was being newly created at the time the trial was planted. The soil was heavily mixed with 6mm sharp gravel to make it free draining. The three plants of each entry were kept together and spaced according to the same distances, but the entries were arranged aesthetically in a mixed border with other species.
How plant health was managed
Diseases
Stemphylium leaf spot was found when the plants arrived for propagation. This disease is common in container-grown plants.
During autumn and spring, the fungus downy mildew appeared, causing discolouration to the upper surface of leaves and forming grey mould underneath. Infected leaves and shoot tips were pruned, and diseased material was removed, but the spread was difficult to control. Susceptible and resistant plants were noted.
Plant Health found Phytophthora root rot and waterlogging in two entries showing dieback.
Weather
April 2021 was the UK’s coldest April since 1922, leading to plant damage at RHS Wisley.Winter 2021/22 brought strong winds and additional bark chips were added to the least hardy shrubby Veronica for protection, while summer 2022 was dry, with a record high temperature of 38.6°C. In December 2022, the temperature dropped suddenly to -8.1°C following a mild autumn, causing frost damage. Clear skies overnight led to intense radiation frost, which caused most of the damage across RHS Wisley.
The trial at RHS Wisley was devastated. Only Veronica odora ‘New Zealand Gold’ and two Veronica pimeleoides ‘Quicksilver’ plants survived. The trial was removed in April 2023.
RHS Harlow Carr had fewer losses, with a more gradual temperature drop to -5.3°C. Gritty soil and surrounding plants likely offered protection. Plant assessments continued into 2023 at this garden, with final recommendations made in November.
How to grow shrubby veronicas
Explore all the information you need to know to grow and care for shrubby veronicas in your garden.
Discoveries from the trial
June 2023
Growing the same trial at two locations gave us the perfect opportunity to study how hebes perform in Yorkshire vs Surrey. Flowering times at RHS Harlow Carr were found to be on average a month later than RHS Wisley. Winter foliage colour was also noted to be stronger at RHS Harlow Carr. Veronica odora ‘New Zealand Gold’ produced yellow shoot tips at RHS Harlow Carr but not at RHS Wisley. This was thought be related to soil magnesium levels.
September 2022
The Veronica flowers were very attractive to pollinators, the trial was a food source across a long season with all the different flowering times. An ivy bee was photographed by Helen Bostock for the first time at RHS Wisley while visiting the trial in September 2022.
Who was involved?
Judges of the trial
The shrubby Veronica judges included: Ian Ashton (Trial Chair, Lowaters Nursery), Charles Carr (Hillier Nurseries), David Godsmark (Grower and agronomist), Steve Harding (Hebe Society Chairman and National Collection Holder), Nigel Hutchinson (Hebe Society Vice Chair, National Collection Holder), Adrian Marskell (The Bransford Webbs Plant Company), Lewis Normand (Garden Designer), Kevin Pratt (Horticulturalist and garden speaker), Rachel Vernon (Bluebell Arboretum and Nursery), Robert Vernon (Snr) (Bluebell Arboretum and Nursery), Alex Waterfield (Plumpton College).
Suppliers to the trial
- Lowaters Nursery (no longer trading), with help from the Hebe Society
- The Bransford Webbs Plant Company
- RHS Wisley Garden Centre
- Seiont Nurseries
- The Hedgerow
- Plumpton College, The Douglas Chalk Hebe Collection
List of plants in the trial
Handy tools and information
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Gardening advice
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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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