Viola, overwintering trial results 2023–2024

Objectives and purpose of the trial

The focus of this small follow-on trial was on Viola varieties that performed well in a display at RHS Hyde Hall, Essex in spring 2022. For the 2023/24 trial, the RHS Trials team wanted to not only compare, record and display the merits of new and established cultivars for the RHS Award of Garden Merit (AGM), but also see how they performed when overwintering.
View of violas in the trial beds at RHS Wisley in May 2024
Violas on display in pots around the Trial Garden at RHS Wisley

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
  • 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
  • Flowering performance
  • Colour and appeal

  • Winter hardiness
  • Pests and disease resistance

Viola AGM winners

This trial was a chance to show off a display of pretty Viola flowers through winter and spring and allowed the judges to grant six new AGMs and retain two AGMs, updating the list of existing AGMs to reflect the current availability of the best violas to buy for overwintering.

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

Why the AGM was awarded

New AGM winners with forum comments and hardiness ratings

Viola ‘Bel Viso Yellow Jump Up’ (Bel Viso Series) AGM (H5) 2024

  • Forum comment: Fabulous plants with impact that have consistently performed over the trial. Good colour appeal and flowering performance and uniform habit. No pest damage and no deadheading required. Flowers look great even in the low light
  • Average height and spread: 30cm x 20cm

Viola ‘Bel Viso Beacon Flash’ (Bel Viso Series) AGM (H5) 2024

  • Forum comment: Plants have a neat habit with flowers of an appealing colour. This has improved with consistent habit and attractive blue flowers
  • Average height and spread: 20cm x 20cm

Viola cornuta ‘Floral Power Blue Picotee’ (Floral Power Series) AGM (H5) 2024

  • Forum comment: These plants showed promise from the start of the trial with a pretty flower colour. The flower has lovely appeal and the habit became more consistent as the plants matured
  • Average height and spread: 20cm x 20cm

Viola cornuta ‘Rocky Denim Jump Up’ (Rocky Series) AGM (H5) 2024

  • Forum comment: Plants have good, uniform habit and flower coverage. The plants filled out over time with increased flowering coverage. The flowers stand up well and are a vibrant deep blue colour
  • Average height and spread: 30cm x 20cm

Viola cornuta SORBET XP DELFT BLUE ('PAS733551') (Sorbet XP Series) AGM (H5) 2024

  • Forum comment: Good sized plants. Good colour combination with attractive face. Very consistent plants and long-lasting colour
  • Average height and spread: 20cm x 20cm

Viola ‘Bel Viso Deep Marina’ (Bel Viso Series) AGM (H5) 2024 – subject to availability

  • Forum comment: Establishing with good flowering performance and lovely colour. Matured with consistent habit and attractive pale blue flowers
  • Average height and spread: 20cm x 20cm
Retained AGMs with forum comments and hardiness ratings

The following two entries were included in the trial as plants with an existing AGM award for comparison. However, as these are summer flowering varieties, they are not comparable. Therefore the trial was inconclusive for these varieties and so they retain the AGM award.

  • Viola sororia ‘Albiflora’ AGM (H5) 2002
  • Viola ‘Inverurie Beauty’ AGM (H5) 1993
Forum judging the Viola trial at RHS Wisley in May 2024
Colourful violas in full bloom during trial at RHS Wisley

AGMs rescinded

For this Viola trial, no existing RHS Award of Garden Merit (AGM) selections lost their AGM.

Plants and location

What was planted?

Sixteen Viola varieties, including some existing AGMs, were 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 took pictures of the plants as they grew, recording when they started and finished flowering.

Where was it planted?

Young Viola plants were carefully planted out intially in a border and then moved to a dedicated trial bed in the Trials Garden at RHS Wisley, Surrey. 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 pests, diseases and weather, violas can be affected by slug and pest damage as young plants
  • Violas flower over a long time, which can potentially 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.

Cultivation

Planting process

The trial was initially planted out with young plants in a Welcome border in early November 2023. However, to allow the plants to be assessed for longer, the young plants were moved to a dedicated trial bed in late February 2024.

Each of the 16 Viola varieties consisted of 16 plants that were arranged in four rows of four plants, with approximately 30cm between 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.

As the trial continued, the team 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 plant health was managed

Challenges

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.

Weather

It was a reasonably mild winter, but there was a week in January 2024 of frosts and freezing temperatures down to minus 7.5 °C, which the plants coped with. This was followed by a very wet and cool spring, which kept the plants in check until late May 2024 when it warmed up and the plants filled out.

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Plant portait of AGM winner Viola ‘Bel Viso Yellow Jump Up’ (Bel Viso Series) AGM (H5) 2024
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Young violas planted in Welcome border at start of trial in November 2023
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Plants moved to new trial bed at RHS Wisley in February 2024
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Plant portait of AGM winner Viola ‘Bel Viso Yellow Jump Up’ (Bel Viso Series) AGM (H5) 2024
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Young violas planted in Welcome border at start of trial in November 2023
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Plants moved to new trial bed at RHS Wisley in February 2024
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Discoveries

While carrying out the trial, a lot of time was spent observing the plants, and details were noticed that did not relate to the formal trial assessment. Here are some of the interesting findings from the trial:
Viola ‘Bel Viso Deep Marina’ (Bel Viso Series) AGM (H5) 2024

2023–2024

It was noted that the majority of plants were into the eighth month of flowering by the final judges’ visit, demonstrating the value these Viola varieties bring by flowering all through winter and spring. It was also recognised that the majority of these entries had also performed well in the spring display at RHS Hyde Hall in 2022.

Did you know?

Violas and pansies are both part of the Viola genus. Typically pansies have fewer and larger flowers, whereas violas have more smaller flowers.

Who was involved?

Judges of the trial

The Viola trial was assessed by 10 experts, with backgrounds in plant nurseries, garden management and garden centres, and members of the RHS Herbaceous Plant Expert Group and RHS Tender Ornamental Expert Group.

The panel visited the trial on four separate occasions during spring 2024 – 14 February, 27 March, 1 May and 5 June 2024 to assess the performance of the entries and highlight those worthy of an AGM.

The Viola judges included: Mike Smith (Chair, Plant Nursery), Andy Bunker (Plant Retail), David Creese (RHS Tender Ornamental Expert Group), Adele Dyer (Plant Trials), Chris Finlay (Plant Breeding), David Foreman (RHS Herbaceous Plant Expert Group), Phil Johnson (Plant Breeding), Duncan Mclean (Plant Retail), Philip Oostenbrink (Head Gardener) and Cathy Rollinson (RHS Herbaceous Plant Expert Group).

Suppliers to the trial

List of plants in the trial

View all the violas trialled at RHS Wisley
  • Viola ‘Bel Viso Beacon Flash’ (Bel Viso Series)
  • Viola ‘Bel Viso Deep Marina’ (Bel Viso Series)
  • Viola ‘Bel Viso Pineapple Crush’ (Bel Viso Series)
  • Viola ‘Bel Viso Yellow Jump Up’ (Bel Viso Series)
  • Viola ‘Inverurie Beauty’
  • Viola cornuta CORINA WHITE (Corina Series)
  • Viola cornuta SORBET XP DELFT BLUE (‘PAS733551’) (Sorbet XP Series)
  • Viola cornuta SORBET XP PRIMROSE BLOTCH (‘PAS975381’) (Sorbet XP Series)
  • Viola cornuta ‘Deltini Violet Face’ (Deltini Series)
  • Viola cornuta ‘Deltini White’ (Deltini Series)
  • Viola cornuta ‘Deltini Yellow and Purple’ (Deltini 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 sororia ‘Albiflora’
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For more information on our RHS Plant Trials or to access older trial reports, please get in touch with our team via email at trials@rhs.org.uk.

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