A Peek at RHS Wisley’s Trials Field

Imagine looking through a seed or plant catalogue, but you can see everything growing away in front of you instead. That’s what visiting a trials field is like. I’ve been to several, and my absolute favourite is the one at the Royal Horticultural Society’s garden at Wisley.

It’s part of what I think of as ‘Secret Wisley’ as it’s tucked away in one of the further corners of the garden. Anyone can go there, but most visitors walk up Battleston Hill then turn back before having a look to see if there’s anything on the other side. It’s a shame, because every gardener benefits from the work carried out there.

If you’ve ever bought a plant with an Award of Garden Merit (AGM), then it’s probably been assessed at Wisley. Some plants are trialled elsewhere – and this is set to increase in future – but the majority currently achieve their AGM (or not) via the trials field.

What makes a plant deserve an AGM?

These are plants that perform. An AGM is awarded to those that are:

  • Available
  • Of good constitution
  • Excellent for ordinary use in appropriate conditions
  • Reasonably resistant to pests and diseases
  • Stable in form and colour

Having an AGM can make a major difference to availability. For instance, two new lobelia were withdrawn from sale, but were reintroduced after their AGM designation led to an increase in demand. How often has the AGM influenced your choice of plants?

How are plants chosen?

Around 30 plants are trialled each year, usually chosen from those where there’s been a significant increase in the choice of new cultivars. Once the shortlist of trials is confirmed, experts such as growers, suppliers, and members of the relevant RHS committees decide which ones will be grown in each trial. They may also provide the plant or seed material needed, or the RHS sources them from suppliers offering them for sale.

The number of cultivars per trial depends on the number of new introductions and how wide a variety that plant has in general. In 2016’s trials Physocarpus has 21 cultivars, and Agapanthus the largest at 150. Not all cultivars grown are new ones; some existing AGM ones are included as a benchmark, and those seen as still performing well at the end of the trial will have their AGM reconfirmed.

It’s not only about ornamental plants; fruit, herbs and vegetables are also assessed e.g. this year’s trials include strawberries in hanging baskets and growing bags. You can imagine my delight at being let loose in their fruit cage to taste them for myself, the day after the trials committee had made their assessment.

How are plants trialled and assessed?

For each trial, a list of judging criteria is drawn up depending on the those agreed as key to a successful result e.g. for 2016’s sweet pepper trial these are quality, appearance, thickness of flesh, taste-raw, and sweetness.

Plants are trialled for at least two seasons, so performance under a variety of conditions e.g. weather, pest attack etc. can be assessed. The number of seasons varies; fast growing plants like dwarf pinks and annuals are two season trials, the peony one currently underway goes on for six. All cultivars in a trial are planted at the appropriate time and grown in the same way, according to the conditions needed for that plant to do well.

Sometimes plants need more of a helping hand. There’s a badger set on site at Wisley, so the current sweetcorn trial is protected by an electric fence. If only we could have one for ours up at the allotment.

Plenty of information boards show what’s going on at the trials field, and visitors may also be asked to choose their favourites amongst the hundreds of cultivars on display. It’s like being let loose in a vast plant sweetie shop!

Further information

To find out more about the RHS trials and the AGM see: rhs.org.uk/trials

For the full list of AGM plants see: rhs.org.uk/AGMplants

If you visit Wisley, look out for the AGM Border which showcases a number of those plants with the award.

Michelle Chapman is a gardener, freelance writer and blogger from Wiltshire. She is the author of the award winning blog, Veg Plotting, where she writes about her small town garden, seasonal food and anything else which strikes her whilst up at her allotment.