Chilli peppers trial results 2023

Objectives and purpose of the trial

The objectives of the trial was to focus on chilli peppers (Capsicum) suitable for culinary purposes, avoiding those of very high heat and the smaller ornamental types. The RHS Trials team wanted to assess a range of chilli peppers for the RHS Award of Garden Merit (AGM) and to demonstrate their cultivation.
View of chilli pepper trial in glasshouse at RHS Wisley
Rows of chilli peppers growing as part of trial at RHS Rosemoor

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:

  • Plant habit
  • Fruit abundance and uniformity

  • Fruit skin quality
  • Disease resistance

Chilli pepper AGM winners

This successful cross-site trial involved a wide variety of chili peppers grown at three RHS Gardens. The cultivars that received AGMs demonstrated strong performance across all trial locations, showcasing healthy plants with good growth habits and a high yield of quality fruit. Additionally, they experienced minimal issues with pests and diseases. As a result of the trial, three new cultivars were granted an AGM, four cultivars had their AGM reconfirmed, and two cultivars had their AGMs rescinded. The list of AGMs now reflects the current availability of the best chillies to grow.

Capsicum baccatum 'Spangles'
  • 0.5–1 metres
  • 0.5–1 metres
<em>Capsicum</em> <em>baccatum</em> 'Spangles'
Capsicum annuum var. annuum (Longum Group) 'Hot Thai'
chilli pepper 'Hot Thai'
  • 0.5–1 metres
  • 0.1–0.5 metres
<em>Capsicum</em> <em>annuum</em> var. <em>annuum</em> (Longum Group) 'Hot Thai'
Capsicum annuum (Longum Group) 'Fuego'
chilli pepper 'Fuego'
  • 0.1–0.5 metres
  • 0.1–0.5 metres
<em>Capsicum</em> <em>annuum</em> (Longum Group) 'Fuego'
Capsicum baccatum 'Spangles'
  • 0.5–1 metres
  • 0.5–1 metres
<em>Capsicum</em> <em>baccatum</em> 'Spangles'
Capsicum annuum var. annuum (Longum Group) 'Hot Thai'
chilli pepper 'Hot Thai'
  • 0.5–1 metres
  • 0.1–0.5 metres
<em>Capsicum</em> <em>annuum</em> var. <em>annuum</em> (Longum Group) 'Hot Thai'
Capsicum annuum (Longum Group) 'Fuego'
chilli pepper 'Fuego'
  • 0.1–0.5 metres
  • 0.1–0.5 metres
<em>Capsicum</em> <em>annuum</em> (Longum Group) 'Fuego'
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This was probably the most challenging trial I’ve been involved with, due to the sheer volume of entries, and the diversity of shape, size, colour and taste.

Ian Clemens, Chair of RHS Rosemoor judging forum

Why the AGM was awarded

New AGM winners with forum comments and hardiness ratings

Capsicum annuum ‘Radiance’ AGM (H1C) 2023

  • Forum comment: Consistent plant with unusual yellow fruits that are hot and sweet. Nice sized, well formed fruit
  • Final height and spread: 80cm X 55cm

Capsicum annuum ‘Reggae’ AGM (H1C) 2023

  • Forum comment: Attractive, even and compact plants with a lot of fruit. Nice open habit. Interesting patio type with neat plants and plenty of fruit
  • Final height and spread: 75cm X 70cm

Capsicum baccatum ‘Spangles’ AGM (H1C) 2023

  • Forum comment: Interesting and novel plant with round, purple fruit, finally turning red. Ornamental, strong and bushy, with open habit. Lots of thick-fleshed fruit
  • Final height and spread: 70cm X 70cm
Reconfirmed AGMs with forum comments and hardiness ratings

Capsicum annuum ‘Apache’ F1 AGM (H1C) 2006

  • Forum comment: Compact and bushy. Strong habit with a lot of fruit for the size of plant. Ornamental, with fruit presented well and all the way up the plant
  • Final height and spread: 65cm X 60cm

Capsicum annuum (Longum Group) ‘Fuego’ AGM (H1C) 2006

  • Forum comment: Plenty of even sized fruit and plant holding up well. Fruit nicely spaced out as held on long petioles
  • Final height and spread: 95cm X 55cm

Capsicum annuum var. annuum (Longum Group) ‘Hot Thai’ AGM (H1C) 2013

  • Forum comment: Heavy yield. Very compact and ornamental, so good for small spaces. Bullet-shaped fruits
  • Final height and spread: 60cm X 65cm

Capsicum annuum ‘Hungarian Hot Wax’ AGM (H1C) 2006

  • Forum comment: Early variety with excellent yield of good-sized fruit that is held well. Consistent plants with healthy leaves and good range of different coloured fruits
  • Final height and spread: 85cm X 60cm
Chilli pepper trial assessment at RHS Wisley in late 2023
Forum assessment of chilli pepper trial at RHS Rosemoor in 2023

AGMs rescinded

These selections were found to no longer be worthy of the AGM, and they will be removed from the AGM list. The forum recommended to rescind the RHS Award of Garden Merit from the following entries:
AGMs rescinded with forum comments

Capsicum annuum ‘Etna’

  • Forum comment: Clustered fruit, so pest and disease issues and rotting. Low yield. Different shaped fruit in top clusters on all plants. Dark healthy foliage but rolling leaves

Capsicum annuum ‘Navaho’

  • Forum comment: The judging criteria for plant habit and fruit abundance were not met due to the plants only having a few leaves and flowers and the plants being inconsistent with large blocky fruit

Plants and location

What was planted?

The trial included 43 chilli pepper entries submitted by various seed companies in the UK. As part of the trial, those awarded an AGM were informally tested to check they had some heat, Chilli heat is measured in Scoville Heat Units (SHU), indicating the concentration of the chemical capsaicin, which gives chillies their heat. They range from mild (50–2,500 SHU) to extra hot (100,000–500,000 SHU). This trial focused on medium (2,500–30,000 SHU) to hot (30,000–100,000 SHU) chillies. SHU ratings can vary due to growing conditions and ripeness.

Where was it planted?

The trial took place at three sites: RHS Bridgewater, Greater Manchester and RHS Rosemoor, Devon in unheated poly-tunnels and RHS Wisley, Surrey in an unheated glasshouse. Seeds of each trial entry were initially sown in early February 2023 in heated propagation areas. Here are some considerations for sowing and planting out the chilli peppers:

  • By growing chillies, you can enjoy a range of colours, shapes, flavours and levels of heat
  • As tender plants, chillies are best grown in a greenhouse, however, they can also be grown outdoors in a sunny spot, in pots or in the ground
  • These plants generally like similar growing conditions to tomatoes

  • Sow seeds indoors from late winter to mid-spring – chillies generally need a long growing season, and an early start will give you an earlier and longer harvest
  • Chilli seeds need warmth to germinate – around 21°C (70°F) so use a warm windowsill or heated propagator

Did you know?

The Guinness World Record for the world’s hottest chilli was awarded to ‘Pepper X’, with 2.69 million Scoville Heat Units (SHU), in August 2023. This beat the previous world record of 1.64 million (SHU) held by ‘Caroliner Reaper’.

Cultivation

Planting process

At each site, RHS Bridgewater, RHS Rosemoor and RHS Wisley, the young chilli pepper plants (three plants per entry) were potted-on in mid-April 2023 and put into their final 7.5l pots by the end of May 2023, using an all-purpose, peat-free compost and then potted on in a prop mix.

How plant health was managed

Challenges

Biological controls were used to manage pests such as aphids, glasshouse whitefly, two-spotted spider mites and thrips during the trial. Caterpillars were removed by hand.

Watering and maintenance
The plants were watered by hand (and at RHS Wisley by drip irrigation in the later stages), with high potassium fertiliser applied. As the plants grew, taller entries were staked to prevent them from bending or breaking. As part of the trial, plants were harvested at regular intervals, with one plant of each entry left unharvested.
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Plant portrait of AGM winner Capsicum baccatum ‘Spangles’ (H1C) 2023
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Young chilli pepper plants at RHS Wisley ready to be potted on in April 2023
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More established chilli pepper plants at RHS Bridgewater ready for final pots in May 2023
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Plant portrait of AGM winner Capsicum baccatum ‘Spangles’ (H1C) 2023
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Young chilli pepper plants at RHS Wisley ready to be potted on in April 2023
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More established chilli pepper plants at RHS Bridgewater ready for final pots in May 2023
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Who was involved?

Judges of the trial

The chilli pepper trial was assessed by the Vegetable Trial Assessment Forums at RHS Bridgewater (26 July and 30 August 2023), RHS Rosemoor (16 August and 6 September 2023) and RHS Wisley (8 August and 31 August 2023). Across the three chilli pepper forums, the members brought expertise and experience in the following areas: Vegetable growing, showing and judging, plant nurseries and retail, horticultural journalism and RHS Fruit, Vegetable and Herb Committee (FV&H) members.

The chilli pepper judges included: Barry Newman (RHS Wisley Forum Chair and RHS FV&H Committee Member), Ian Clemens (RHS Rosemoor Forum Chair and RHS FV&H Committee Member), John Constable (Formerly with Elsom Seeds and Allium Seeds), Keith Hine (National Vegetable Society Judge), Richard White (Former Trial Garden Manager, Tozer Seeds), Britta Horsthemke (Estate Gardener), Duncan Palmer (Vegetable grower), Jon Wheatley (Horticulturist, designer, RHS Shows and Britain in Bloom), David Allison (RHS Bridgewater Forum Chair and RHS FV&H Committee Member), Mark Fletcher (Head of Agronomy, National Institute of Agricultural Botany), Joe Lofthouse (Team Leader Edibles at RHS Harlow Carr), James Oakey (Buying Director, Hayloft Plants), Roy Roberts (Senior plant breeder of vegetables, MRL Seeds Ltd), Sue Stickland (Writer on vegetable growing and Director of Wales Seed Hub) and David Thornton (Exhibition grower and National Vegetable Society Secretary).

Suppliers to the trial

List of plants in the trial

View all the chilli peppers trialled at RHS Wisley, RHS Rosemoor and RHS Bridgewater
  • Capsicum annuum (Longum Group) ‘Fuego’ AGM (H1c) 2006 
  • Capsicum annuum [Fresno mixed] 
  • Capsicum annuum ‘Aci Kil’
  • Capsicum annuum ‘Anaheim’
  • Capsicum annuum ‘Apache’ AGM (H1c) 2006 
  • Capsicum annuum ‘Barkol’
  • Capsicum annuum ‘Bullet’
  • Capsicum annuum ‘Cayennetta’
  • Capsicum annuum ‘De Cayenne’
  • Capsicum annuum ‘Etna’ AGM (H1c) 2006 
  • Capsicum annuum ‘Gusto Green’
  • Capsicum annuum ‘Holy Peak’
  • Capsicum annuum ‘Hot Rod’
  • Capsicum annuum ‘Hungarian Hot Wax’ AGM (H1c) 2006 
  • Capsicum annuum ‘Longhorn’
  • Capsicum annuum ‘Mirch Masala’
  • Capsicum annuum ‘Navaho’ AGM (H1c) 2006 
  • Capsicum annuum ‘Orange Pepperoncini’
  • Capsicum annuum ‘Orange Tyger’
  • Capsicum annuum ‘Pencil’
  • Capsicum annuum ‘Radiance’
  • Capsicum annuum ‘Reggae’
  • Capsicum annuum ‘Romital’
  • Capsicum annuum ’Sahem’
  • Capsicum annuum ‘Sparky’
  • Capsicum annuum ‘Super Tramp’
  • Capsicum annuum ‘Toofan’
  • Capsicum annuum ‘Trinidad Perfume’
  • Capsicum annuum ‘Vampire’
  • Capsicum annuum var. annuum (Longum Group) early jalapeño 
  • Capsicum annuum var. annuum (Longum Group) ‘Hot Thai’ AGM (H1c) 2013  
  • Capsicum annuum var. annuum (Longum Group) jalapeño 
  • Capsicum annuum ‘Vindaloo’
  • Capsicum annuum ‘Zimbabwe Black’
  • Capsicum baccatum ‘Aji Delight’
  • Capsicum baccatum ‘Aji Habanero’
  • Capsicum baccatum ‘Havana Gold’
  • Capsicum baccatum ‘Lemon Drop’
  • Capsicum baccatum ‘Spangles’
  • Capsicum chinense ‘Machu Pichu’
  • Capsicum ‘Lancer’
  • Capsicum ‘Red Flame’
  • Capsicum ‘Slowburn’
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