Diascia (twinspur), annual bedding trial results 2024

Objectives and purpose of the trial

The focus of this trial was on  bedding selections of Diascia (twinspur) cultivars. The last time Diascia was trialled at the RHS was in 1995 at RHS Wisley, Surrey and since then, new selections have been introduced. The RHS Trials team aimed to assess and compare new and established annual bedding cultivars over one summer for the RHS Award of Garden Merit (AGM) and to see how they performed. An extention of this trial includes the perennial Diascia trial, running for two summers.
View of Diascia plants growing in trial beds at RHS Wisley
Beautiful Diascia plants in the trial beds during summer 2024

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
  • Flower power

  • Vigour
  • Pest and disease resistance

Diascia, annual bedding AGM winners

This colourful summer Diascia display showcased a variety of annual bedding plants that withstood a cold and wet spring. It allowed the judges to grant four new AGMs and retain two AGMs, updating the list of existing AGMs to reflect the current availability of the best Diascia annual bedding plants to buy and grow at home.

A cold and wet spring hampered this trial. Only the toughest plants were chosen so the new AGMs really have the wow-factor.

David Creese, RHS Tender Ornamental Expert Group

Why the AGM was awarded

New AGM winners with forum comments and hardiness ratings

Diascia ‘Diamond Light Pink’ AGM (H3) 2024

  • Forum comment: Flower power! Lots of good, large soft pink flowers with dark eyes. Good vigour. Consistent, even habit
  • Average height and spread: 25cm x 45cm

Diascia FLYING COLOURS LIGHT PINK (‘Dala Litpink’) (Flying Colours Series) AGM (H3) 2024 – also sold as DARLA LIGHT PINK

  • Forum comment: Fantastic. Intense flower colour, lots of flowers. Good bloomer from the beginning.
  • Average height and spread: 20cm x 20cm

Diascia ‘Aurora Dark Pink’ (Towers of Flowers Series) AGM (H3) 2024

  • Forum comment: Dark, rose pink flowers, filled out late in the season. Colour stands out and old seedheads enhance rather than detract
  • Average height and spread: 35cm x 30cm

Diascia ‘Aurora Apricot’ (Towers of Flowers Series) AGM (H3) 2024

  • Forum comment: Wow! Upright habit and spires of flowers. Flowers fading harmoniously, not tatty. Uniform, vigorous and full of flower
  • Average height and spread: 45cm x 40cm
Voted AG (not quite meeting the full AGM criteria) with forum comments

Diascia BREEZEE PLUS WHITE (Breezee Series)

  • Forum comment: Put on good growth, good habit, consistent shape and size. Slow starter

Diascia ELFJES DAANTJE (Elfjes Series)

  • Forum comment: Late flowering. Pure white flowers, medium size. Lax habit, consistent

Diascia JULIET WHITE (‘Baljalite’)

  • Forum comment: Bright white flowers. Habit open. Consistently good. New flowers opening within the foliage, not visible enough. Too many old flowerheads

Diascia ‘Aurora Cherry Blossom’ (Towers of Flowers Series)

  • Forum comment: Unusual spire flower form, dense spikes. Flowers clustered together. Flowers white with strong pink centres. Habit upright, even and rigid

Diascia BREEZEE PLUS APPLE BLOSSOM (Breezee Series)

  • Forum comment: Big flowers with intense eye colour. Lax habit, good for a container or hanging basket

Diascia DIVARA BLUSH (Divara Series)

  • Forum comment: Nice flowers, plants small and dense. Strong early in the season

Diascia ‘Divara Giga Rose’ (Divara Series)

  • Forum comment: Spreading habit, lacking flower power. Late season

Diascia FLYING COLOURS ROSE (Flying Colours Series)

  • Forum comment: Some good individuals. Bushy habit. Good intense flower colour, flowers all over. Improved. Some flower bleaching, mixed opinions on whether this adds to the display

Diascia barberae JULIET PINK WITH EYE (‘Baljulpiney’)

  • Forum comment: Open habit, attractive and well covered with flowers. Hasn’t been consistent, flower power coming too late

Diascia PICCADILLY HOT PINK (‘Kledb10714’)

  • Forum comment: Good flowers from the beginning. Yellow foliage

Diascia ‘Divara Giga Salmon’ (Divara Series)

  • Forum comment: Good flower power but slow to fill out. Bleaching affecting lower lip of flowers

Diascia FLYING COLOURS DEEP SALMON IMPROVED (‘Dala Depsam’) (Flying Colours Series)

  • Forum comment: Strong flower colour, spreading. Bloomed well from the beginning

Diascia LITTLE DREAMER (‘Pender’)

  • Forum comment: Compact with small flowers. Solid performer

Diascia LITTLE DRIFTER (‘Pendrif’)

  • Forum comment: Soft orange flowers, densely packed. Holding habit.

Diascia BREEZEE PLUS ORANGE (Breezee Series)

  • Forum comment: Large flowers, big plants, some plants splitting in the middle. Some bleaching

Diascia barberae JULIET ORANGE (‘Balajulor’)

  • Forum comment: Reddy-orange flowers. Intense flower colour, not fading much. Shy of flower

Diascia PICCADILLY ORANGE (Piccadilly Series)

  • Forum comment: Luminous orange flowers. Uniform. Upright form
Forum judging Diascia trial at RHS Wisley in July 2024
Judging of Diascia trial at RHS Wisley in September 2024

AGMs rescinded

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

Plants and location

What was planted?

This trial included 54 different selections of bedding Diascia. These were all sourced and submitted by breeders and growers from the UK and the Netherlands.

Where was it planted?

Young plug plants and seed-sown entries were carefully planted out in two dedicated trial beds in the Trials Garden at RHS Wisley, Surrey. Here are some considerations for planting out Diascia annual bedding plants:

  • Diascias perform best in well-drained soil
  • Plants tend to be pest and disease free, but might be damaged by slugs and snails when young
  •  Check the predicted final size of the Diascia. Some grow taller while others have a more trailing habit

  • You can buy diascias as plug plants or small plants. Keep plants bought in the spring protected from frosts before planting them out
  • Diascias grow well in the ground and in containers, providing long-lasting flowering displays

Diascia facts

There are diascias with flower colours ranging from white, through pale pink to red and orange.

Cultivation

Planting process

Most of the Diascia annual bedding entries arrived as plug plants at RHS Wisley in February 2024. These were potted on into 8 x 8 biodegradable pots and kept under cover at the RHS Propagation Facility. Two entries arrived as seed and were sown around 20 March 2024.

The trial was then planted out across two beds in the Trials Garden in May 2024. Eight plants of each entry were planted out in rows, with 40cm between plants in a row, and 40cm between each row. The beds were covered with strulch (a straw based mulch), to act as a weed suppressor.

The plants were fed once a week, initially with a water-soluble fertiliser and then with a balanced seaweed feed. No deadheading was carried out during the flowering season, to assess which entries continued to flower over the summer.

Heavy spells of rain caused flower drop across the trial in September 2024, but all entries reflowered. At the end of the flowering season, as each entry went over, the plants were cut back to a dome. The plants were left over winter to assess which entries survived through to early 2025.

How plant health was managed

Challenges

Flower bleaching was found to affect the flowering display, mostly in the red and orange flowered selections, causing white patches to form on the flowers. With the softer flower colours, bleaching was less noticeable and sometimes even added to the overall display.

Weather

Spring 2024 saw high rainfall and low sunshine hours. This contributed to a slow start to flowering across the trial.

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Plant portrait of AGM winner Diascia ‘Diamond Light Pink’ AGM (H3) 2024
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Diascia annual bedding entries kept in RHS Propagation Facility in February 2024
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Garden team planting our young Diascia plants for the trial in May 2024
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Plant portrait of AGM winner Diascia ‘Diamond Light Pink’ AGM (H3) 2024
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Diascia annual bedding entries kept in RHS Propagation Facility in February 2024
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Garden team planting our young Diascia plants for the trial in May 2024
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Did you know?

Few pollinators were observed visiting the trial. Diascia are pollinated by a specialised solitary, oil-collecting bee in their native South Africa, the Rediviva bee, that can reach into the long flower spurs with its long front legs to collect oil.

Who was involved?

Judges of the trial

The Diascia annual bedding trial was assessed by a seven-person judging group. The forum was made up growers, horticulturalists and plant writers, including members of the RHS Tender Ornamental Expert Group. During the trial in 2024, there were four forum meetings held from June to September.

The Diascia annual bedding judges included: Paul Hansord (Chair, former Manging Director of Thompson and Morgan), David Creese (Westminster Parks, RHS Tender Ornamental Expert Group member), David Ford (Trials Coordinator for RHS Tender Ornamental Expert Group), Yvonne Walker (Plant Retail, former Manging Director of Hayloft Plants), Christopher Young (RHS Wisley Garden Manager, Formal and Decorative display, and RHS Tender Ornamental Expert Group member), Graham Rice (Garden Writer) and Duncan McLean (RHS Senior Plant Buyer).

Suppliers to the trial

List of plants in the trial

View all the Diascia annuals trialled at RHS Wisley
  • Diascia ‘Aurora Apricot’ (Towers of Flowers Series)
  • Diascia ‘Aurora Cherry Blossom’ (Towers of Flowers Series)
  • Diascia ‘Aurora Dark Pink’ (Towers of Flowers Series)
  • Diascia barberae ‘Apricot Queen’
  • Diascia barberae JULIET ORANGE (‘Balajulor’) Ball Colegrave
  • Diascia barberae JULIET PINK WITH EYE (‘Baljulpiney’)
  • Diascia barberae JULIET RED (‘Baljuled’)
  • Diascia BREEZEE PLUS APPLE BLOSSOM (Breezee Series)
  • Diascia BREEZEE PLUS APRICOT (Breezee Series)
  • Diascia BREEZEE PLUS ORANGE (Breezee Series)
  • Diascia BREEZEE PLUS PINK (Breezee Series)
  • Diascia BREEZEE PLUS RED (Breezee Series)
  • Diascia BREEZEE PLUS WHITE (Breezee Series)
  • Diascia ‘Diamond Dark Orange’
  • Diascia ‘Diamond Fuchsia’
  • Diascia ‘Diamond Light Pink’
  • Diascia ‘Diamond Pink’
  • Diascia ‘Diamond White Blush’
  • Diascia DIVARA BLUSH (Divara Series)
  • Diascia DIVARA DEEP RED (Divara Series)
  • Diascia ‘Divara Giga Orange’ (Divara Series)
  • Diascia ‘Divara Giga Rose’ (Divara Series)
  • Diascia ‘Divara Giga Salmon’ (Divara Series)
  • Diascia DIVARA ORANGE (Divara Series)
  • Diascia DIVARA PINK (Divara Series)
  • Diascia DIVARA RED 4622 Exp i5
  • Diascia ‘Divara Salmon’ (Divara Series)
  • Diascia DIVARA WHITE (Divara Series)
  • Diascia ELFJES DAANTJE (Elfjes Series
  • Diascia ELFJES DOORTJE (‘Sumdia 01’) (Elfjes Series)
  • Diascia ELFJES JASPER (‘Sumdia 08’) (Elfjes Series)
  • Diascia ELFJES JOCHIE (‘Sumdia 03’) (Elfjes Series)
  • Diascia ELFJES ROSE XXL (Elfjes Series)
  • Diascia ELFJES SALMON XXL (Elfjes Series)
  • Diascia FLYING COLOURS ANTIQUE ROSE (‘Diastu’) (Flying Colours Series)
  • Diascia FLYING COLOURS APPLEBLOSSOM (‘Diastara’) (Flying Colours Series)
  • Diascia FLYING COLOURS DEEP SALMON IMPROVED (‘Dala Depsam’) (Flying Colours Series)
  • Diascia FLYING COLOURS LIGHT PINK (‘Dala Litpink’) (Flying Colours Series)
  • Diascia FLYING COLOURS ORANGE (Flying Colours Series)
  • Diascia FLYING COLOURS RED (‘Diastonia’) (Flying Colours Series)
  • Diascia FLYING COLOURS ROSE (Flying Colours Series)
  • Diascia FLYING COLOURS WHITE (Flying Colours Series)
  • Diascia GENTA PINK (Genta Series)
  • Diascia JULIET WHITE (‘Baljalite’)
  • Diascia LITTLE DANCER (‘Pendan’)
  • Diascia LITTLE DREAMER (‘Pender’)
  • Diascia LITTLE DRIFTER (‘Pendrif’)
  • Diascia PICCADILLY APPLEBLOSSOM (‘Kledi04015’) (Piccadilly Series)
  • Diascia PICCADILLY DARK RED (‘Kledb11787’) (Piccadilly Series)
  • Diascia PICCADILLY DARK SALMON (‘Kledb18008’) (Piccadilly Series)
  • Diascia PICCADILLY HOT PINK (‘Kledb10714’) (Piccadilly Series)
  • Diascia PICCADILLY ORANGE (Piccadilly Series)
  • Diascia PICCADILLY WHITE (‘Kledb24020’) (Piccadilly Series)
  • Diascia ‘Rose Queen’
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