Helianthus (sunflower) Fleuroselect trial results 2024
Objectives and purpose of the trial
View of sunflowers from the entrance to Floral Fantasia at RHS Hyde Hall
Trial beds bursting with sunflowers 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:
- Flower performance
- Habit
- Colour and appeal
- Pest and disease resistance
- Longevity
Sunflower AGM winners
We had a challenging start to the trial with unprecedented wet and cold weather in spring, which had a detrimental effect on the seeds sown outside. However, the weather did not prevent us from showcasing a broad range of different sunflowers thanks to the nursery staff at RHS Hyde Hall.
Why the AGM was awarded
Forum judging the sunflower trial at RHS Hyde Hall
Pollinator enjoying time on a sunflower during the summer
AGMs rescinded
Plants and location
What was planted?
Where was it planted?
The sunflower seeds were sown directly into the open ground in Floral Fantasia area at RHS Hyde Hall, Essex, and six entries, submitted as young plants, were planted directly into trials beds. Here are some considerations for planting out sunflowers:
- Sow seeds indoors in early spring to give them a head start
- Slugs and snails like to feast on young annual sunflowers, so it is worth waiting until your seedlings are strong, resilient and hardened off well to give them the best chance
- Position in full sun and in a sheltered spot
- Sunflowers like plenty of water, so consider applying a layer of mulch such as strulch to help retain moisture levels in the soil
Cultivation
Planting process
Additional soil analysis concluded that the soil in each trial bed was high in nutrients and organic matter. This was taken into consideration when selecting a mulch for the trial, which needed to be low in organic matter and nutrients. Therefore, strulch was selected for its ability to improve soil structure without overloading the soil with excess nutrients.
Once ready, the Floral Fantasia trial beds were marked out in April 2024 into 86 rows, ready for sowing of the seed entries in early May 2024, with a second sowing in early June 2024 (this was done in two batches to extend the length of the display for visitors). Each of the entries (consisting of five plants) were arranged in height order according to the heights detailed by their suppliers. The entries were spaced 64cm apart and the five plants within each entry were spaced 40cm apart.
Due to the unprecedented wet and cold weather, very few of these sowings were successful. Seeds were also sown under glass in the nursery at RHS Hyde Hall in June 2024, with the view that they would replace any seedlings in the trial beds that failed to produce a young plant.
In early July 2024, the remaining six cultivars, supplied as young plants (dervived from cuttings), were planted straight into the ground on arrival.
Soon after the seedlings and young plants had established, a thin layer of strulch (a straw-based mulch) was applied to the soil. The horticulturists working on the trial were careful to leave a space between the plants and the strulch to avoid damaging the young plants and seedlings. The strulch helped to retain moisture levels in the soil throughout the trial.
Watering was only carried out during the hot weather to prevent them from drying out.
How plant health was managed
Challenges
After sowing, the trial beds were covered with netting to prevent birds from eating the seeds. Once the seedlings and young plants had established, a thin layer of strulch was applied to the ground to supress slug and snail damage. The horticulturists on the trial found the strulch successful at supressing weeds and slugs. During the trial, no significant disease or pest damage was observed.
Pruning and deadheading
It was decided by the judging panel that the sunflowers should not be deadheaded during the course of the trial.
How to grow sunflowers
Explore all the information you need to know to grow and care for sunflowers in your garden
Discoveries
2024
The trial brought in a lot of goldfinches as the sunflowers went over, which attracted lots of visitors to the trial area in autumn. Many visitors enjoyed trying to capture the birds on camera, while others simply enjoyed watching them from a bench. Plant sunflowers and leave the spent flower heads to ripen seeds to attract goldfinches into your garden.
Who was involved?
Judges of the trial
In addition to this, the panel were sent up-to-date images of the entries in mid-September 2024 via email, so they could assess later-flowering entries one more time before casting their final vote. Once the judges concluded their overall assessment of the sunflowers, the results were reviewed by the RHS Herbaceous Plant Expert Group.
The Fleuroselect sunflower judges included: Mike Smith (Chair, Owner, WD Smith & Son Nurseries), David Creese (RHS Tender Ornamental Expert Group member), Phil Johnson (RHS Herbaceous Plant Expert Group member and Director, Lion Seeds), Boyd Douglas-Davies (Managing Consultant, The Boyd Foundation), Alan Bourne (Owner, Perrywood’s Garden Centre), Adele Dyer (Principal Researcher and Writer, Which), Andy Bunker (Sales Director, Alton’s Garden Centre), Chris Finlay (Sales Director, Volmary), Michael Perry (Presenter and Influencer, Mr Plant Geek) and Molli Christman (RHS Horticulturist).
Suppliers to the trial
Fleuroselect Members:
- Burpee Europe B.V.
- Evanthia
- Suttons
- Benary
- Thompson & Morgan
- Dobies
- EconSeeds
- H.M. Clause
- Johnsons
- Mr. Fothergill’s
Extended trials area:
List of plants in the trial
Handy tools and information
- Full article - Filter for AGM plants and refine by colour, height and season of interest
Find an AGM plant online
Filter for AGM plants and refine by colour, height and season of interest - Full article - Explore advice and helpful tips from our resident experts
Gardening advice
Explore advice and helpful tips from our resident experts - Full article - Check how hardy plants are using the RHS hardiness ratings system
Hardiness ratings
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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 trials@rhs.org.uk.
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