RHS overhauls its plant awards system

The RHS has revised its plant awards system, and thrown out the dead wood (and a few hostas).

'Anny’s Winter Orange’ and 'Ghost' plants
Promoted: 'Anny’s Winter Orange’ and 'Ghost' Credit: Photo: JUDY WHITE/GARDENPHOTOS.COM

Probably close to 80,000 different plants are available to British gardeners from nurseries, garden centres and seed companies. More than 2,000 different hostas and 3,600 roses have been listed by nurseries in recent years. But which are the best and how do we choose?

In 1922 the Royal Horticultural Society (RHS) set out to help by creating its Award of Garden Merit (AGM). Unlike the society’s other awards which were often given after inspecting cut stems in a vase, this award is based on how well plants actually grow in gardens.

Unfortunately, the award never really caught on, so in 1992 it was relaunched, as the society’s premier award, to be revised at 10-year intervals. Since then, RHS trials have been the most valuable route by which plants have been added or removed, together with round-the-table discussions by both amateur and professional experts.

So now the award has undergone another comprehensive overhaul, with detailed input from the RHS plant committees, specialist societies, Plant Heritage National Collection holders and other experts. As a result, almost 1,900 plants have lost their AGMs, including 25 per cent of all the AGM vegetables, and more than 1,400 plants have gained awards. In all, 58 new vegetables and herbs have been added (but no fruit), plus 26 new maples (eight dropped), 74 new hostas (10 cut) and four dahlias (more than 40 cut). The list now runs to 7,073 plants.

Plants have been removed because they are no longer available, have been superseded by better plants, have become susceptible to pests or diseases, are not sufficiently uniform and for various other reasons. Plants have been added simply because they are very good garden plants. It has also been realised that a 10-year cycle cannot keep up with the pace of change, so the award will now be updated annually.

Dr John Grimshaw, director of the Yorkshire Arboretum at Castle Howard, co-ordinated the process. He says: “The 2012 AGM review was conducted by hundreds of people bringing a huge weight of experience to the table, meaning that these plants really have been thoroughly scrutinised. I think it’s significant that a core of more than 5,000 plants have retained the AGM, demonstrating its essential strength.

“Almost 300 irises and 270 chrysanthemums are out of the list because they aren’t available; 340 fruit and vegetables are out for lack of availability. Apart from a group such as heathers, where the closure of a couple of nurseries has meant a great many cultivars are no longer available, the removal of 1,900 AGMs should not be taken as worrying or negative, more that the list has been given a good pruning to remove the dead wood.

“Most other deletions are because the plants concerned simply aren’t up to the high standards expected of an AGM.”

In the opinion of many (including myself), the list still needs refining. It still contains plants which are not sold anywhere and are certainly not “reasonably easy to find” as the RHS puts it. Also, most bedding plants, whose cultivars now change with great rapidity, await a separate review and while orchids, including hardy orchids, have been added, work continues on lilies and water lilies. And only two hellebores? I’m sure the annual reviews will deal with these issues.

Personally, I was sorry to see Bergenia 'Glasnevin’ dropped. It was outstanding in the recent trial, both for flowers and for its winter foliage, but nurseries no longer seem to list it. Others I’m sad to see go include Campanula persicifolia 'Chettle Charm’, Clematis Josephine, Prunus serrula and some old British-bred daylilies. Rosa Margaret Merril also goes but, strangely, the disease-prone Iceberg is retained.

However, I was pleased to see the back of Bergenia x schmidtii (the leaves always hide the flowers), Euphorbia characias subsp. wulfenii (too variable, better to buy a named form), Geranium 'Johnson’s Blue’ (the more recent 'Orion’, 'Blue Cloud’ and others are better), Robinia pseudoacacia 'Frisia’ (prone to disease - and there’s one on every corner) and Malus x zumi 'Golden Hornet’ (another martyr to disease).

In all, this is a big step forward. As well as the revised list of AGMs, the Society’s system of rating plants for their hardiness has also been revised, which brings the AGM right up to date. With its annual revision, the system can now stay up to date and anomalies that slipped through this huge and complex process can quickly be resolved.

New RHS hardiness waitings

H1a Warmer than 15C/59F Tropical plants for indoors and heated greenhouses

H1b 10 to 15C/50 to 59F Subtropical plants for indoors and heated greenhouses

H1c 5 to 10C/41 to 50F Warm temperate plants for outdoors in summer

H2 1 to 5C/34 to 41F Plants needing a frost-free greenhouse in winter

H3 -5 to 1C/23 to 34F Plants generally hardy outside in mild areas

H4 -10 to -5C/14-23F Plants hardy outside in most of the UK in an average winter

H5 -15 to -10C/5-14F Hardy outside in most of the UK in severe winters

H6 -20 to -15C/-4 to 5F Hardy outside in the UK and northern Europe

H7 Colder than -20C/-4F Hardy outside in the severest European climates

What makes an AGM plant?

At the same time as the list of AGM plants has been revised, the criteria have been loosened. So, previously plants had to be “of outstanding excellence”, now they need only be “excellent”. And while previously only plants that did “not require specialist growing conditions or care” could be included, now they are only required to grow “in appropriate conditions”.

This is better for specialist growers with some experience but less helpful to newcomers to gardening looking for plants for their new garden.

Now, Award of Garden Merit plants must be:

- Excellent for ordinary use in appropriate conditions.

- Of good constitution.

- Essentially stable in form and colour.

- Reasonably resistant to pests and diseases.

- Available to buy in the UK.

AGMs won and lost

Dr Grimshaw picked out these plants and gave reasons why they have been promoted or demoted.

Winners

Athyrium 'Ghost’ “An exquisite hybrid, ferns were comprehensively reviewed”

Begonia 'Benitochiba’ “Wonderful pink foliage”

Cornus sanguinea 'Anny’s Winter Orange’ “Outstanding winter stem colour”

Galanthus elwesii 'Comet’ “An outstanding cultivar [of snowdrop]”

Juglans regia 'Broadview’ “Self-fertile reliable fruiting clone [of walnut]”

Losers

Cuprocyparis leylandii “Simply undesirable to recommend an uncontrollable thug”

Cotoneaster horizontalis “Potentially invasive. The RHS can’t promote such plants”

Geranium wallichianum 'Buxton’s Blue ’ “Seed-raised, very variable… superseded by Rozanne ('Gerwat’)”

Hosta fortunei var. albopicta “Superseded by many much better cultivars e.g. 'Patriot’ ”

Rosa 'Madame Isaac Pereire’ “Superseded by many Austin cultivars”

Find an overview of the new hardiness ratings system

Graham Rice blogs on this issue at TransatlanticGardener.com