Notes on Wisley's Trials Field

Today I'm going to have a closer look at the RHS Award Of Garden Merit (AGM) and the trials field at Wisley as promised a couple of weeks ago. I'd asked if I could have a look around when I went to the flower show and the RHS kindly arranged for me to be shown around by Andrew McSeveney, the trials manager.

Whilst I was waiting for Andrew to meet me, I took the above photo of half of the trials field. I was tutting about those people getting in the way, only for Andrew to tell me they were the Dahlia Assessment Panel who were meeting to assess this year's trials! Much deep discussion was in evidence, with the occasional raising of hands. No doubt all will be revealed in due course when the RHS produce the trials reports plus details of any AGMs awarded. NB it's well worth browsing through the trials database - available online (also have a look at the list of Plant Bulletins available) - especially if you're thinking about a particular plant for your garden or plot. They're a goldmine of information about each variety trialled.

In my Postcard From Wisley, a number of you asked if anyone can visit the trials field. Yes, it's open to all and can be found by walking up the hill where the double borders are, past the Henry Moore sculpture and once you're over the brow of the hill, you'll see the trials field in front of you. There's a big new pavilion at the bottom of the field, should you be in need of a rest before looking around the trials themselves.

Just before going into the field it's worth pausing at the entrance as there's a large board showing what's being trialled and where. As it was towards the end of the season quite a few of the beds were in the process of being cleared and others had caliente mustard (a crop which helps with soil hygiene because it's a biofumigant) or a green manure growing in them. The beds which were still going strong each had a display board describing the plants being trialled.

As well as the trials themselves, one section of the field holds the national collection of rhubarb (RHS Harlow Carr is also the national collection holder and Andrew told me each RHS site has different rhubarb cultivars) and another part currently houses a botany trial where Bergenia are being grown to solve identification and nomenclature problems.

A wide variety of plants are trialled each year: annuals, perennials, shrubs, fruit and vegetables. Andrew told me they're trying to align the trials with the RHS' campaigns and objectives e.g. Grow Your Own. Another factor are any horticultural developments e.g. if a particular plant has had lots of new cultivars introduced, then it becomes a prime candidate. The various plant committees recommend which plants should be considered for a trial and it's up to them to provide a case to the RHS detailing the reasons why. Sometimes trials are international, such as the current one for Vinca, the results of which will be particularly of interest in Germany apparently.

Trials for 2012 will include:
  • Clematis
  • Saxifraga
  • Dahlias
  • Sweet peas
  • Alpine Dianthus
  • Euphorbia
  • Stipa
  • Salvia (sub-shrubby)
  • Lettuce
  • Parsley
  • Tomatoes
  • Basil
We talked a lot about the criticism that the trials only show which plants grow well at Wisley. This is being looked at in some detail: the RHS are keen to involve Further Education colleges and schools in the trials. Harlow Carr has trialled Meconopsis and broad beans this year and a nearby nursery has also been involved in the trials. This is so a protocol can be put together to ensure consistent trialling of plants away from Wisley. You may also remember I also took part in a couple of RHS trials when I grew radishes one year and then peas. Whether there'll be people like me involved again remains to be seen as collating the results from us all was time consuming. I hope we are.

Andrew also told me that a good trial result at Wisley doesn't necessarily guarantee an AGM, nor does a poor result discount an award either. The experience of the people on the assessment panel (usually drawn from specialist nurseries, societies and national collection holders as well as appropriate RHS representatives) means they can also judge how well plants perform elsewhere. All this goes into the decision melting pot for the awards. There's no limit to the numbers awarded the AGM: if a plant meets the AGM criteria, then it will get the award.

Whilst the trials field is one of the most interesting aspects of Wisley (in my view), some of you might be put off by the lack of garden context. This is where the above AGM border comes into its own :)

My chat with Andrew also highlighted some unexpected aspects of trialling. Whilst we were walking past the Lobelias in their hanging baskets and pots, he told me a supplier was concerned that their cultivars weren't being trialled fairly. Apparently their Lobelia had been bred to need less water and so weren't performing as well as their thirstier cousins. Andrew explained that all the plants are cared for in the same way, i.e. in the way we would grow them and to introduce different growing regimes would negate the results of the trial.

NB plant hardiness isn't one of the aspects trialled because a plant that isn't hardy doesn't mean it isn't garden (or greenhouse or conservatory) worthy. Hardiness is assessed separately and is given alongside the AGM information to help us decide whether a plant will do well in our garden. The RHS have just announced a revised hardiness rating of 7 levels and I expect their website will be updated soon with more details.

Lots more information on the AGM can be found on the RHS website. It's also in the process of being revised and will be relaunched in 2013 - as I have some information on what's being looked at, I can post about this another time if anyone's interested.

My thanks go to Andrew for being so generous with his time on a very busy day and to Erin O'Connor for arranging for me to meet up with him.


  1. Sounds really interesting. I sue the trial reports quite a bit, it's great they are made available. I'm glad they are working on making the trial more applicable to other areas of the country though. Will watch out for the results of the tomato and basil trials!

  2. Hi Janet - it was fantastic. I've been wanting to have a good look around for ages. So glad you're making use of trials reports, they're so useful and need to be publicised more in my view.


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