RHSRHS PlantPlant TrialsTrials andand AwardsAwards Hardy Geraniums – Stage 1 James Armitage Botanist, RHS Garden Wisley Bulletin Number 10 June 2005 www.rhs.org.uk RHS Trial of Hardy Geraniums Staging a Trial of Hardy Geraniums Entries The great number of geraniums available to gardeners There were 136 entries in the Trial, submitted as plants by meant that a comprehensive assessment of the genus could nurseries in the UK , Holland and USA, by collection not be achieved in one trial without most of the Wisley holders and by individuals (listed on p.13). Trials Field being given over to their cultivation. For this reason the Trial of Hardy Geraniums was divided into three The majority of entries in Stage 1 were cultivars, hybrids or staggered stages. The composition of each stage was variants of the following species: decided by Geranium experts Elizabeth Strangman and David Hibberd based on cultivation requirements and G. asphodeloides G. oreganum G. saxatile taxonomic relationship. In Stage 1 geraniums best suited G. clarkei G. palmatum G. transbaicalicum to a bright spot were grown. Many of the plants in this G. collinum G. pratense G. traversii Stage were from the Pratense Group, which includes G. gymnocaulon G. pyrenaicum G. yeoi species such as G. himalayense, G. clarkei and G. pratense G. himalayense G. regelii itself, joined by representatives of other species that enjoy G. ibericum G. renardii plus South ϫ similar conditions. Stage 2 was mainly comprised of G. magnificum G. ruprechtii African species G. ϫ oxonianum cultivars with selections of G. psilostemon, G. sanguineum and summer dormant species also assessed. Stage 3 included species such as G. macrorrhizum, G. phaeum and G. sylvaticum which benefit from a little shade. To complete the set a separate trial of geraniums suitable for the rock garden was also conducted. Elizabeth Strangman David Hibberd Objectives ⅷ To recommend the Award of Garden Merit to those plants considered the best for garden decoration ⅷ To compare the large number of new cultivars with older established plants ⅷ To demonstrate and recommend different methods of cultivation ⅷ To establish correct nomenclature ⅷ To describe, photograph and take herbarium specimens of entries as a permanent record of the trial for future reference. Records ⅷ Flowering period – start and end of flowering ⅷ Height and spread ⅷ Staking – required or not ⅷ Habit – groundcover, spreading, mound-forming, scrambling ⅷ Evergreen – retention of foliage over winter ⅷ Hardiness Front cover: Geranium ‘Sirak’ Right: Geranium ‘Blue Cloud’ 2 RHS Plant Trials and Awards Cultivation of Stage 1 Award of Garden Merit (AGM) Three plants of each entry were planted on 9 July 2002 on a prepared site. The soil on the Trials Field, though sandy Geranium ‘Blue Cloud’ (H4) 2004 and free draining, is rich in nutrients, due to it being Geranium ‘Brookside’ (H4) 2004 extensively cultivated for various trials. The soil has a pH of 7.5. Generally, hardy geraniums perform best on a soil Geranium ‘Mavis Simpson’ (H4) 2004 of medium to low fertility soil, so no fertiliser was added. Geranium ‘Nimbus’ (H4) 2004 Many of the entries in Stage 1 required staking, this was Geranium ‘Orion’ (H4) 2004 done in April before strong growth had begun, using birch Geranium palmatum (H3-4) 1993 Reconfirmed or hazel twigs up to a height of 2m. Geranium pratense (H4) 1993 Reconfirmed After flowering all plants, with the exception of the South ‘Mrs Kendall Clark’ African species, were cut right down to the ground. This Geranium pratense (H4) 1993 Reconfirmed not only made the plants tidier by removing the seed ‘Plenum Violaceum’ heads and dead foliage, but gave them a new lease of life and encouraged a second flush of flowers. Over winter Geranium ϫ riversleaianum (H4) 1993 Reconfirmed many entries proved to be evergreen, forming attractive ‘Russell Prichard’ mounds of foliage. The trial concluded after three years, at Geranium ‘Sirak’ (H4) 2004 which time most plants would have benefited from being divided. Award of Garden Merit subject to Pests verification of cultivar name The most frequently encountered pests found on any Geranium ϫ magnificum ‘Rosemoor’ hardy geraniums are: Capsid bugs: Sap-feeding insects active from mid May to end of August. Their feeding on the shoot tips cause leaves Award of Garden Merit rescindments: to develop with many tiny holes. It will be recommended that the AGM be rescinded from the following at the next review of the Award in 2012 Geranium sawfly: Greenish-grey, caterpillar-like larvae with black heads that live on the underside of the leaves where Geranium clarkei ‘Kashmir White’ AGM(H4)1996 they make rounded holes. Damage occurs during May – September. The damage is mostly cosmetic. Geranium ϫ himalayense AGM(H4)1993 ‘Gravetye’ Glasshouse red spider mite: A sap-feeding pest mainly found in late summer on hardy geraniums. The tiny mites Geranium ‘Johnson’s Blue’ AGM(H4)1993 cause a fine pale speckling on the upper leaf surface. Geranium renardii AGM(H4)1993 Vine weevil: It is the larval stage that causes problems by eating the roots. This leads to poor growth and sometimes (H4) = hardy throughout the UK the death of plants. Several plants in the trial were killed (H3-4)= may require some protection over winter in some by this pest. parts of the British Isles Leaf and bud eelworms: These are microscopic worm-like creatures that live inside the foliage, causing infested areas The Award of Garden Merit to dry up and turn brown. This pest was found in the trial To gain this award a plant must: plants but in most gardens will be overlooked. ⅷ be excellent for ordinary garden use Andrew Halstead ⅷ be available PRINCIPAL ENTOMOLOGIST ⅷ be of good constitution ⅷ be reasonably easy to grow ⅷ be reasonably resistant to pests and diseases ⅷ be essentially stable in form and colour Judging The trial was assessed for the Award of Garden Merit by the Floral Trials Subcommittee using the following criteria: ⅷ habit ⅷ vigour (health) ⅷ floriferousness ⅷ length of flowering period ⅷ foliage Hardy Geraniums – Stage 1 3 The genus Geranium ‘It is hard to imagine gardening without hardy geraniums. In Geraniums in the wild their midst are plants that are totally indispensable. They are Few genera are more suited as a whole to horticultural use resilient, versatile, and offer something for every garden than Geranium and the qualities of hardiness, adaptability situation. Rich in colour and generous in display, the best hardy and ease of propagation that have fitted them so well to geraniums are deserving of any mixed border. RHS AGM trials the garden have also encouraged their spread in the wild. are essential in order to pinpoint the truly excellent plants that every gardener should have. The RHS AGM is certainly one of More than 420 species of Geranium are currently the most important aspects of the work of the RHS.’ recognised and they are found on every continent on Earth, except Antarctica, usually in moist, temperate Fergus Garrett, regions. Such conditions prevail over much of northern HEAD GARDENER AT GREAT DIXTER Eurasia and North America and across mountainous areas further south and it is from these places that many of our garden favourites, such as G. phaeum, G. himalayense and Geranium or geranium? G. maculatum, originate. These species tend to be Pelargonium is a genus of about 280 shrubby or herbaceous perennial, forming bold plants in meadows or open species mostly native to South Africa. They are most woodland. Where conditions become warmer around the familiar to gardeners as the brightly coloured hybrids Mediterranean and Arabian peninsula there are a greater grown for containers and summer bedding. The confusion number of annual and summer dormant species. In several that persists between this genus and Geranium – the hardy areas of the world geraniums grow at such high altitudes geraniums or cranesbills – is due in part to the great that they have become true alpines; much smaller plants Swedish botanist Carolus Linnaeus. In his monumental adapted to shallow soils and low temperatures. As is often work Species Plantarum (1753) Linnaeus included all the the case species inhabiting islands are amongst the most Pelargonium species under Geranium and it was by the latter eccentric, the Madeiran endemic G. maderense is a huge name that they first became known to the gardening monocarp while the Hawaiian G. arboreum forms a shrub. public. In 1789 the French botanist L’Héritier made clear the differences between the two genera but the damage was Geraniums in the garden done and, to the frustration of gardeners and botanists The hardy geraniums are undoubtedly one of the most alike, Pelargonium is still known by the common name popular groups of garden plants. They are beautiful, geranium. Pelargonium is distinguished by having umbels of reliable and endlessly various, and today’s stunning irregular-shaped flowers, fewer fertile stamens and a nectary hybrids are the modern flag bearers of a genus with a long tube. Two other genera are generally included in the family history in British gardens. There are no records to tell us Geraniaceae, the rock garden favourites Erodium and the when herb Robert (Geranium robertianum) was first used for tender genus Monsonia which now encompasses the its healing properties, or its ornamental relatives G. succulent species formerly known as Sarcocaulon. pratense, G. sanguineum and G. sylvaticum for their beauty. Geranium maculatum (above left) with radially symmetric flowers and Pelargonium ‘L’Elégante’ (above right) with bilaterally symmetric flowers demonstrate one of the key differences between the two genera 4 RHS Plant Trials and Awards As British natives their cultivation must date back many hundreds of years. In the late 16th century the first hardy geraniums from continental Europe arrived on British shores and over the next four centuries species were introduced from Asia, the Americas, South Africa and the tooth division antipodes.