Pelargonium (species and hybrids, Stellar, Miniature Stellar, Dwarf Zonal, Zonartic)

The National Plant Collection of pelargoniums at RHS Garden Wisley represents one of the most diverse and carefully curated groups of pelargoniums in the UK. The collection brings together species and cultivars with a wide range of origins, growth habits and horticultural uses. With 423 plants currently held at RHS Wisley, including 383 in the The Glasshouse, the collection offers visitors an opportunity to explore the breadth of this fascinating genus across several specialist growing environments.

When to visit

The collection is at its most impressive from May to June, when many species and cultivars reach their peak flowering period. During these months, visitors can appreciate the full range of colours, scents and leaf forms that make pelargoniums so popular. The whole collection is not on display at all times. Outside the peak season, the collection still offers interest, particularly in the alpine houses where some species follow different seasonal rhythms.

Where to see the collection

The pelargoniums are displayed across several areas at RHS Wisley, each chosen to suit the needs of different species:

• Glasshouse display and service houses: home to the majority of the collection, including tender varieties
• Alpine display houses: these provide cooler, drier conditions ideal for certain species that require a distinct seasonal cycle
• Propagation unit: where young plants, cuttings
  

  A method of growing new plants from parts of an existing plant, such as sections of root, stem, leaf or bud. When prepared correctly and planted in the right conditions, they can produce roots and eventually become independent plants. There is a wide range of different methods for taking cuttings, depending on the plant and time of year.

  and seed-raised specimens are grown on and assessed
• Temperate Glasshouse: an annual display in May near the waterfall

Together, these spaces allow the collection to showcase the full diversity of the genus, from xerophytic species adapted to arid environments to more lush, leafy types, including species and caudex types.

Find some of the collection in The Glasshouse at RHS Wisley

History of the collection

The modern glasshouse collection was significantly expanded in 2021 with major donations from Fibrex Nurseries (who held the collection until 2021) and Stephen Pollard, both well-known names in pelargonium conservation and horticulture. However, RHS Wisley’s connection with the genus stretches back much further. Several long-held specimens date from the early 2000s, and the alpine section houses three particularly early arrivals from 1988, 1989 and 1997. These older plants provide a living link to decades of horticultural work at RHS Wisley and reflect the RHS’s long-standing commitment to plant conservation.

Why they are of interest

Pelargoniums offer a combination of ornamental beauty, botanical diversity and practical uses. Their extended flowering period makes them reliable performers in gardens and glasshouses. Many species have distinctive scents, from citrus to spice, and some have traditional uses in herbal remedies or perfumery. Their varied growth habits – from compact shrubs to sprawling, architectural forms – also make them versatile plants for display and study.

Care and cultivation

Pelargoniums require different levels of water and feed throughout the year:

• Spring: Water every two weeks with a nitrogen-rich feed to support new growth
• Summer: Water weekly. Continue with nitrogen-rich feed until flower buds form, then switch to a potassium rich feed every two weeks to encourage strong flowering
• Autumn: Reduce feeding to once a month as growth slows
• Winter: Stop feeding if plants are entering dormancy
  

  Dormancy refers to a period of inactivity in plants, during which they slow down or stop their growth, conserving energy and resources. This is a natural process that helps them survive harsh conditions, such as winter or drought. Dormancy in seeds is a mechanism that prevents them germinating until environmental conditions are favourable for growth.

  . Water sparingly and only when the compost
  

  Can refer to either home-made garden compost or seed/potting compost: Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

  has fully dried out

Certain taxonomic sections, including species in the Cortusina, Hoarea, Isopetalum, Ligularia, Otidia and Polyactium sections should be allowed to dry out completely once their leaves begin to shed.

All about pelargoniums

Pelargonium ‘Ardens’ is a striking cultivar

Propagation

Propagation is typically carried out using softwood cuttings

Softwood cuttings are taken from spring to early summer (Apr-Jun), using material from the soft and flexible young shoot tips from this seasons growth, which root readily. Use for hardy and tender perennials, deciduous shrubs, climbers and some trees.

taken in late summer. This ensures strong, healthy young plants for the following season. Surplus or woody stock plants are usually removed at the end of the season to maintain the quality of the collection. Seed propagation is also possible, although it carries the risk of producing hybrids. Seedlings

A seedling is a young plant grown from seed.

must therefore be monitored carefully to ensure they remain true to type.

Climate resilience

Many pelargoniums, particularly xerophytic species, are naturally adapted to low rainfall and high temperatures. This makes them well suited to the increasingly variable climate conditions seen in the UK. However, some species have specific requirements. Pelargonium triste, for example, needs a period of cold to trigger flowering. When grown in the glasshouse, this requirement may not be fully met, causing it to flower later than the specimen grown in an alpine department.

Notable and endangered cultivars

• Endangered cultivar
  

  Gardeners often use the word variety when referring to a specific plant, but the correct botanical term is 'cultivar'. Whichever word you use, it means a distinctive plant or plants, given a specific cultivar name and usually bred to enhance certain characteristics, such as flower or fruit size, colour, flavour or fragrance, plant size, hardiness, disease resistance, etc. Additionally, it is worth knowing that, botanically, variety has another meaning - it refers to a naturally-occurring distinct plant that only has slight differences in its looks. For example, Malva alcea var. fastigiata differs from typical plants by having an upright habit.

  : Pelargonium ‘Chinese Coral’, a rare and valued plant within the collection
• Rare species deserving wider cultivation: P. tetragonum, P. acetosum and P. gibbosum, all of which attract strong interest from visitors
• Missing cultivar: Pelargonium ‘Sussex Delight’, which is rare in cultivation and would be a valuable addition to the collection

Pelargonium acetosum is a rare species that deserves wider use

Stories and connections

RHS Wisley has played an important role in the history of pelargonium cultivation in the UK. Pelargonium tongaense was first grown in this country at the garden and a pressed specimen is preserved in the RHS Herbarium. Diana Miller, a former Keeper of the Herbarium, produced one of the most comprehensive reference books on the genus, cementing RHS Wisley’s reputation as a centre of expertise. Pelargonium triste also has historical significance as the first species in the genus encountered by western explorers and the first to be sent back to Europe.

Nicola Hankey

Pelargonium praemosum has a subtle beauty

Some of the team’s favourites are Pelargonium ‘Ardens’, P. praemosum and P. reniforme, each chosen for its distinctive character and horticultural appeal. The pelargonium genus is full of scent, uses and colour. It is a genus that never has a dull day.