Lupinus (lupin) trial results 2024–2025

The AGM is intended to help gardeners choose plants that are likely to perform in their gardens, 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

At the start of May 2024, the RHS Curatorial team carefully planted out the young lupin plants into the trials beds within the Trial Garden. Each trial entry consisted of three lupin plants, arranged in neat rows across the beds to ensure consistency. The plants, which arrived in 9cm pots, were spaced 60cm apart, allowing plenty of room to thrive and fill out over the three-year trial period.

The plants were watered to help them establish and during particular dry periods. As the plants were young and needed to establish root and leaf systems some flowers were removed early in the first year.

As lupins are poisonous, the team took precautions, wearing gloves during handling to ensure safety while working with these striking, plants.

Challenges

The lupin trial began in 2024 with the aim of evaluating plant health performance and establishment under local conditions. The intention was to monitor growth and resilience over the course of the establishment year, with a view to developing best practices for future cultivation.

However, as the trial progressed, several challenges emerged – chief among them a significant outbreak of lupin aphids. These are non-native aphids that can form large colonies in the spring and summer on lupins, and can eventually cause plants to wilt. As is known with lupins, they may be affected by various issues such as mildew, aphid infestation, and lupin anthracnose, which can impact success, and unfortunately, these issues became prominent during the first year.

To try and help address these challenges, the Trials team followed a programme of treatments, and damaged plant material was removed as necessary. Additionally, due to lupin anthracnose, it was the plan to replant two trial beds in 2025 to improve overall growth and give the trial a stronger foundation for the following years, but the aphid infestation meant the team did not continue with this plan.

Treatments

• Powdery mildew: Leaves were removed as part of management, and a soapy solution was used to support plant health
• Lupin anthracnose​: By the end of October 2024, two beds of lupins had been completely cleared due to issues like brown lesions, split and distorted stems, and corkscrewing. Old leaves and infected plant material were removed as part of disease management. The lupin varieties Lupinus ‘Beefeater’ and Lupinus ‘King Canute’ showed resilience during this period
• Lupin aphids: Aphid control methods included hand-squashing and water sprays, which were initially successful, though larger aphids returned and water spraying also helped spread anthracnose. The team then tried a soapy spray and a calcium chloride spray, which again were only temporarily effective

Outcomes

Findings from the trial indicate that the lupin aphid infestation is a regional issue, that is difficult to manage and can build up, causing the plants to wilt. Based on these findings, the only lupin currently holding an AGM – Lupinus arboreus – has been recommended for removal from the AGM list, as advised by the RHS Woody Expert Group.

While the trial ultimately had to be concluded earlier than planned, the challenges faced have provided valuable insights. Each setback has highlighted key areas for refinement in future trials. These learnings will directly inform adjustments to growing methods, pest and disease management strategies, and trial design going forward. Far from being a setback, this trial has laid a strong foundation of practical knowledge to build on.