Viola (overwintering) trial 2023–2024

Objectives and purpose of the trial

This is a small follow-on trial of the Viola display assessed in spring 2022. The 2024 trial will focus on the violas that performed well in the 2022 trial to determine how these plants overwinter. The trial will compare, record and display the merits of new and established cultivars to see how they perform. Those that perform best will be awarded the RHS Award of Garden Merit (AGM).
Violas on display in pots around the Trial Garden at RHS Wisley
Plant portrait of Viola cornuta ‘Rocky Denium Jump Up’

Plants and location

What was planted?

Sixteen Viola varieties, including some existing AGMs are being grown as part of the trial. The pretty flowers provide interest in winter and early spring when there is not much else in flower. They can be grown in the ground but also look good in containers with some varieties being sweetly scented. The RHS Plant Trials team will be taking pictures of the plants as they grow, recording when they start and finish flowering.

Where is it planted?

In the Trials Garden at RHS Wisley, Surrey, each of the 16 entries consisted of 16 young plants that were arranged in four rows of four plants with approximately 30cm between plants. Here are some considerations for planting out violas:

  • The best time to grow violas is during autumn when soil is still warm, allowing roots to establish
  • Violas perform best in free-draining soil
  • Plants can grow and cope well with winter weather and bloom readily in spring

  • Although largely unaffected by pest, diseases and weather, violas can be affected by slug and pest damage as young plants
  • Violas flower over a long time, which can be extended by deadheading spent flowers

Viola facts

Viola cultivars are low growing, free-flowering plants with semi-evergreen indented green foliage. The flowers with five petals have a characteristic shape and appear from winter through to spring.

Judges and criteria

Judges of the trial

The trial judges include 10 experts, with backgrounds in plant nurseries, garden management and garden centres and members of RHS Herbaceous and Tender Ornamental Plant Committees. They will meet to assess the plants in the trial several times in spring 2024.

The 2023–2024 Viola forum includes: Mike Smith (Chair, Plant Nursery), Andy Bunker (Plant Retail), David Creese (Tender Ornamental Plant Committee), Adele Dyer (Plant Trials), Chris Finlay (Plant Breeding), David Foreman (Herbaceous Plant Committee), Phil Johnson (Plant Breeding), Duncan Mclean (Plant Retail), Philip Oostenbrink (Head Gardener) and Cathy Rollinson (Herbaceous Plant Committee).

Judging criteria

The following factors are all taken into consideration as part of the judging of the trial:

  • Habit
  • Flowering performance
  • Colour and appeal  

  • Winter hardiness
  • Pests and disease resistance

Plant portrait of Viola cornuta ‘Sorbet XP Primrose Bloch’
Colourful violas in full bloom during trial at RHS Wisley

Cultivation

Planting process

The trial was planted out in the trial bed in early November 2023 with young plants. The trial was dressed with soil-improving mulch and were fed intermittently with liquid feed. Due to the very wet spring, minimal watering was required.  
 
It was agreed that the first row of four plants would be deadheaded every few weeks to see if this had any effect on flowering performance. The outcome of this was that it gave little or no benefit when compared to the plants that were not deadheaded.

How we’re managing plant health

Early in the season, some plants and flowers were affected by damage, potentially slugs, given the wet spring. As it was also a cold spring, the plants took time to grow away from the impact. The cool, wet weather also resulted in some leaf spotting, such as that caused by the fungus Ramularia. No direct actions were taken to address these issues, however the application of feed should help the plants grow strongly and minimise the impact.

I am always amazed at how hardy violas can be. I’m often asked how long they will flower for and the answer is, that with feeding and deadheading, they will flower until June.

Gemma Burr, Trials Horticulturalist
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Plant portait of Viola cornuta ‘Floral Power Blue Picotee’
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Young violas planted in trial bed at RHS Wisley in November 2023
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Violas starting to grow from April to May 2024
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Plant portait of Viola cornuta ‘Floral Power Blue Picotee’
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Young violas planted in trial bed at RHS Wisley in November 2023
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Violas starting to grow from April to May 2024
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Supplier to the trial

List of plants in the trial

View all the violas on trial at RHS Wisley
  • Viola sororia ‘Albiflora’
  • Viola ‘Bel Viso Pineapple Crush’ (Bel Viso Series)
  • Viola ‘Bel Viso Yellow Jump Up’ (Bel Viso Series)
  • Viola ‘Bel Viso Beacon Flash’ (Bel Viso Series)
  • Viola ‘Bel Viso Deep Marina’ (Bel Viso Series)
  • Viola cornuta ‘Deltini White’ (Deltini Series)
  • Viola cornuta ‘Deltini Violet Face’ (Deltini Series)
  • Viola cornuta ‘Deltini Yellow and Purple’ (Deltini Series)
  • Viola cornuta [Corina White] (Corina Series)
  • Viola cornuta ‘Floral Power Blue Picotee’ (Floral Power Series)
  • Viola cornuta ‘Penny Mickey’ (Penny Series)
  • Viola cornuta ‘Rocky Denim Jump Up’ (Rocky Series)
  • Viola cornuta ‘Rocky Violet Blue’ (Rocky Series)
  • Viola cornuta [Sorbet XP Delft Blue] (‘PAS733551’) (Sorbet XP Series)
  • Viola cornuta [Sorbet XP Primrose Blotch] (‘PAS975381’) (Sorbet XP Series)
  • Viola ‘Inverurie Beauty’
RHS Award of Garden Merit logo
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Handy tools and information

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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