Camassia (quamash) trial 2024–2026

Objectives and purpose of the trial

The RHS has not trialled Camassia (quamash) before, so this is an opportunity to see how the different species and cultivars perform side by side in the same bed at RHS Bridgewater, Greater Manchester. Those that perform best will be awarded the RHS Award of Garden Merit (AGM). Currently, no camassias hold an AGM.
Soft subtle colours of camassias shine in the sun in May 2024
Upright spikes of camassias draw attention in trial bed

Plants and location

What was planted?

The trial features 20 entries of Camassia species and cultivars, showcasing the impressive diversity in flower colour, form, flowering period, reliability, and longevity. Carefully selected for assessment, these cultivars have been generously contributed by breeders and growers from across the UK.

Native to North America, Camassia produce striking upright spires of star-shaped flowers in shades of white, blue, purple, and pink. Flowering in late spring to early summer, they are hardy, low-maintenance plants well suited to borders or naturalistic planting in wildflower meadows.

As part of the trial, photographs will be taken of each entry to document both the overall habit and detailed flower close-ups. The RHS Trials team will also record key growth stages, including what height the flower spikes reach. In addition, the RHS Herbarium may collect a specimen of each entry to preserve in its permanent collection.

Where was it planted?

The spring bulbs were planted into the ground in the The Old Frameyard area at RHS Bridgewater, ready to brighten the coming seasons. Here are some considerations for planting out camassias:

  • Camassia like moist soil in full sun or light shade
  • It is best to plant them between September and November at a depth 2 or 3 times the size of the bulb
  • The leaves usually start to appear in January, followed by the flower stems in April

  • When flowering has finished, remove the stems but leave the foliage to die back naturally as it feeds the bulb for the following year
  • Camassia will grow in containers but flowering diminishes after a couple of years and they dislike
    being disturbed by being repotted

Judges and criteria

Judges of the trial

The trial panel comprises nine experienced horticulturists, including National Collection holders, nursery owners, plant breeders, and members of the RHS Bulb Expert Group. From late April to June each year of the trial, the judges will convene fortnightly to assess the plants, evaluating them from the first blooms to the final flowers. The results will be reviewed by the RHS Bulb Expert Group at its autumn meeting in the final year of the trial, and the RHS Trials team hopes to share the outcomes in early 2026.

The 2024–2026 Camassia (quamash) trial judges are: Sue Wood (Chair, Harrogate Council Horticulturist), Teresa Clements (RHS Bulb Expert Group member), Stella Exley (Camassia National Collection Holder, Hare Spring Cottage Plants), Muhammad Hafiz Ullah (Bulb expert), Peter Williams (Former lecturer), Madeleine Calder (National Trust, Attingham Park), Nigel Hutchinson (The Hedgerow, Threshfield), Carolyn Collins (RHS Plant Records Officer), Vicky Fox (Co-owner of Plantagogo).

Judging criteria

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

  • Overall appearance (proportions, sturdiness, foliage)
  • Flower impact: colour, size, shape and number of florets per spike

  • Length of flowering
  • Pest, disease and weather resistance
  • Uniformity of height and colour

Vibrant camassias make a bold statement in the trial bed
Camassias growing strong at RHS Bridgewater in May 2025

Cultivation

Planting process

In October 2023, Camassia bulbs arrived at RHS Bridgewater, intended for planting in The Old Frameyard later that month. However, exceptionally wet weather conditions delayed the planting schedule, with persistent rainfall rendering the beds unsuitable for preparation.

Improved weather in November 2023 allowed the RHS Trials team, supported by volunteers, to proceed. By the third week of the month, the team was able to prepare the site and plant the bulbs as planned.

Each trial entry consisted of 27 bulbs, arranged in nine plots of three bulbs each. Within each plot, bulbs were planted in a triangular formation, at a depth of twice their height. A spacing of 50cm was maintained between entries to ensure optimal growing conditions. To prevent disturbance by wildlife, the trial bed was covered with chicken wire.

The site was selected for its full sun exposure, though Camassia will tolerate partial shade. The soil is moisture-retentive, and watering will be provided in spring if necessary, during the active growth and flowering period. The bed will be kept dry during the bulbs’ dormant phase. Flower stems will be removed after blooming, while the foliage will be left to die back naturally to replenish the bulbs.

Following the natural die-back period in summer 2025, the bulbs will be lifted and redistributed to other areas of the Outer Walled Garden. A number of the blue-flowered varieties are expected to be replanted in the Blue Peter Garden.

How we’re managing plant health

Managing plant health in this trial has been relatively straightforward, as Camassia are generally not troubled by pests or diseases. However, at RHS Bridgewater, squirrels have posed a minor challenge by digging up some plants, particularly those in pots. To mitigate this, protective wire was used but later removed in early February 2024, once shoots had begun to emerge on about half the entries.
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In April 2025, the camassias come back to life bringing with it swathes of colour
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As the trial beds were prepped in November 2023, chicken wire was used to protect the Camassia bulbs
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Early growth from the camassias begin to show through in March 2024 at RHS Bridgewater
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In April 2025, the camassias come back to life bringing with it swathes of colour
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As the trial beds were prepped in November 2023, chicken wire was used to protect the Camassia bulbs
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Early growth from the camassias begin to show through in March 2024 at RHS Bridgewater
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Discoveries

While carrying out the trial, a lot of time is 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 so far:
Camassia leichtlinii ‘Pink Star’

April 2025 | First emerging flowers

The first plants to flower in 2025 were Camassia leichtlinii ‘Pink Star’, blooming between 16–23 April 2025, and Camassia ‘Blue Candle’, which opened on 23 April 2025. Their early blooms marked a vibrant start to the season.

Did you know?

Traditionally, native North American people used camassias as a food. The bulbs were roasted and eaten as a vegetable, or boiled down into a molasses-like sweet.

Suppliers to the trial

List of plants in the trial

View all the camassias on trial at RHS Bridgewater
  • Camassia ‘Blue Candle’
  • Camassia ‘Blue Heaven’
  • Camassia cusickii 
  • Camassia cusickii ‘Zwanenburg’
  • Camassia leichtlinii ‘Aurora’
  • Camassia leichtlinii Avon’s Stellar Group 
  • Camassia leichtlinii ‘Pink Star’
  • Camassia leichtlinii ‘Sacajawea’ (v) 
  • Camassia leichtlinii ‘Semiplena’ (d) 
  • Camassia leichtlinii ‘Silk River’
  • Camassia leichtlinii ‘Sweet Candle’
  • Camassia leichtlinii subsp. leichtlinii 
  • Camassia leichtlinii subsp. suksdorfii ‘Blauwe Donau’
  • Camassia leichtlinii subsp. suksdorfii Caerulea Group 
  • Camassia leichtlinii subsp. suksdorfii (Caerulea Group) ‘Maybelle’
  • Camassia leichtlinii subsp. suksdorfii ‘Electra’
  • Camassia leichtlinii ‘Violet Candle’
  • Camassia quamash
  • Camassia quamash ‘Blue Melody’ (v) 
  • Camassia quamash ‘Orion’
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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 [email protected].

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