Pelargoniums: History, Varieties, Growing, & Propagation

Pelargoniums: History, Varieties, Growing, & Propagation

By Florence Carey, Master Gardener

 

 

Most gardeners have fond memories of ‘geraniums’ growing on Grandma’s windowsill, or in window boxes of our youth. They are a common and treasured garden and house plants, and have been for centuries! I found it interesting to learn more about where these plants came from, and how it came to be that we have so many different varieties to enjoy in our gardens today.

Geranium or Pelargonium?

Pelargoniums are commonly known as ‘geraniums’, but true geraniums are a separate genus in the same family. Carl Linnaeus originally included all the species in one genus, Geranium, and they were later separated into two genera by Charles Louis L’Héritier de Brutelle in 1789.

 

The Family Geraniaceae includes both: Pelargonium, a genus of flowering plants that includes about 280 species of perennials, succulents, and shrubs, commonly called geraniums, pelargoniums, or storksbills. These are tender herbaceous perennials, which are annuals in our zone; and Geranium, a separate genus of related plants, also commonly known as cranesbills. These are hardy herbaceous perennials, used for permanent plantings, borders, and groundcover.

 

The defining differences between the two are: flower symmetry (each flower of a pelargonium has a single symmetry plane (zygomorphic) like a face or a pansy, which distinguishes it from the geranium, which has radial symmetry (actinomorphic), like a circle or a daisy); and number of stamens (pelargoniums have from two to seven, and geraniums have 10 or more).

History and Development of Pelargoniums

Pelargoniums are native to South Africa and Australia. The first seeds were brought to Europe and grown by the English plant collector, John Tradescant, and the Dutch governor of Cape Town sent cuttings to Holland in the 17^th century. In the 18^th century, the first pelargoniums reached the U.S.A., possibly via the West Indies, and Francis Masson, a Scottish horticulturalist, introduced 50 species, later perishing at sea searching for more plants. I like to imagine the adventures and dangers of exploring for new species, and that the plants I propagate today are the distant descendants of some of those plants.

 

In the 19^th century, pelargoniums were cultivated by the thousands, and entire greenhouses were devoted to them; however, pelargoniums fell somewhat out of favour between the World Wars, due partly to the cost and availability of fuel to heat greenhouses. Popularity was regained in the second half of the 20^th century. Hybridization has been of great interest ever since the process of pollination was first understood in Victorian times (late 19^th century). In the 1950s, Professor Craig of Pennsylvania State University succeeded in breeding modern seed-raised strains which are still popular today. In the 1970s, Miss Frances Hartsook bred the Unique hybrids in the U.S.A., Reverend Stringer introduced the long-flowering double-flowered Deacon or floribunda strain in the U.K., and Ted Both introduced the Stellar or straph strain in Australia.

 

Ongoing developments continue, with the introduction of wider colour ranges, including true yellows, double-flowered forms of ivy-leaved and zonal geraniums, regals with more compact growth habit and shorter flowering stalks, and improved resistance to disease.

 

Pelargoniums are popular all over the world. Most are hardy only to zones 10 to 11, so cannot be wintered outdoors here. They have a long flowering period, with flowers mostly in red, orange, or white, but intensive breeding has produced a huge array of cultivars with great variety in size, flower colour, leaf form, and aromatic foliage. Today, pelargoniums come in a broader range of colours, or bi-coloured with petals edged, speckled, or softly suffused with contrasting colour. There is increasing interest in less usual forms, such as miniatures, for patio gardening, and scented-leaved types grown mainly for foliage.

Physiology

 

 

 

The leaves of pelargoniums are usually alternate on the stem, palmately lobed, or pinnate, often on long stalks, and sometimes with light or dark patterns. The leaves of ivy-leaved geranium (Pelargonium peltatum) have a thick cuticle, better adapting them for drought tolerance.

 

The flowers are spectacular. Erect stems bear five-petalled flowers in umbel-like clusters, which are occasionally branched. Flowers open from the centre outwards, a form of inflorescence referred to as pseudo-umbels. The lower three (anterior) petals are differentiated from the upper two (posterior) petals. The posterior sepal is fused with the pedicel to form a hypanthium (nectary tube), which varies from a few millimetres to several centimetres. Stamens vary from two to seven, and there are five stigmata in the style.

Not for Pollinators

A study in England found that pelargonium was not attractive to pollinators compared to other plants. They are eaten by some caterpillars, but none native to North America. In my experience, I don’t see pollinators visiting my pelargoniums. Deer and rabbits don’t seem to eat them either. If you choose to grow pelargoniums, it’s for their beauty, and not to create habitat for local creatures and insects.

Primary Groups

These are the forefathers of all the cultivar groups. The definition of a species is that it breeds true and is to be found doing this in the “wild”. There is a large diversity of characteristics in habit, shape, size, and colour of species pelargoniums.

 

Primary Hybrids. These are recognised as being the resultant plant from a first-time cross between two different known species. Usually, but not always, primary hybrids are sterile.

 

Zonal or Garden. These are named for the dark ring or “zone” on the leaves. Common names include storksbill, fish, or horseshoe geraniums. They are easy to grow, with hundreds of cultivars available. They are a bush-type plant, foliage seven inches above the pot, and can grow to five feet in frost-free areas. Stems become woody with age; young growth is tender and succulent. Umbels are up to six inches in diameter, each made from five to 200 individual florets, and may be single or double. They have a long bloom time, from early summer to early fall, and at 13°C or warmer, will flower all year. There are also dwarf plants (five to seven inches), miniature plants (less than five inches), micro-miniature plants (less than four inches), as well as Deacon (a genetic hybrid with double flowers) and Stellar varieties (a genetic hybrid with distinctive half-star-shaped leaves and slim-petalled blooms which appear star-shaped).

 

 

Ivy-leaved. These are named for their peltate or shield-like lobed leaf, resembling ivy. Common names include trailing, cascade, hanging, or basket geraniums. They have leathery, waxy leaves, and grow three feet long (or up to 15 feet where frost-free).They can be used as ground cover, hanging pots, or trained against walls or pergolas. The stems are brittle, and there are fewer colours available, with mauves and pinks most common. They are also greedy with water and food.

 

Regal. Many of these originate from Royal greenhouses in England. Common names include show, fancy, grandiflora, or decorative and in the U.S.A. as Lady or Martha Washington.They have unzoned, slightly furry, serrated leaves, and the grandest, most dramatic flowers with florets up to two inches across. Most are single, but ruffled, fringed, or frilly edges make them appear double. There is a broad colour range, including white, pink, mauve, orange, near black, but no true blue or yellow. Many are bi-coloured, with richly contrasting tints, veins, or blotches. They have a shorter bloom-time, and are suited to greenhouses.

 

 

Angel. These are classed as miniature or dwarf regals and commonly called pansy-faced geraniums. All have single, five-petalled flowers, mostly in the mauve colour range, often marked with a deeper colour. They are compact and bushy plants and long-flowering. They are growing in popularity due to many new varieties being released by specialist nurseries.

 

Unique. These don’t fit into any of the other categories, and their parentage is confused and obscure. Generally, they are shrubby and woody evergreens, with distinctly scented leaves, and small flowers with blotched and feathered petals. They may have bicoloured foliage.

 

Scented-leaved. These may be species or hybrids and are grown chiefly for fragrance, which occurs in nature to discourage grazers and encourage pollinators. The leaves vary in size, may be solid or deeply lobed or lacy, shiny, or mat or velvety, and some variegated. Scents include lemon, apple, orange, peppermint, pine, rose, and other less-defined aromas. Flowers are less prominent, sparce, and mostly unscented. The scented leaves are used for potpourri or as flavourings in cooking, or grown for the oil geraniol, which is an essential oil much used commercially in perfumery. Be sure to look for (and smell) some of these in the herb garden at Assiniboine Park in summer.

 

Growing Pelargoniums

Most pelargoniums prefer full sun and well-drained, fertile soil, and will benefit from pruning to produce a bushier plant and deadheading to encourage more blooms. Younger plants will naturally form a single unbranched stem unless the top is pinched out (at four to six inches), and regularly after that. Indoor plants will benefit from time outdoors in summer, where exposure to sunlight ripens the wood and makes the plant healthier.

Propagating Pelargoniums

Softwood cuttings root easily in water or directly in potting mix. Use a three-inch pot, or a five-inch pot for up to five cuttings, inserted around the sides, where drainage is best. They may also be grown from seeds. Sow thinly inside four months before the last frost and do not cover. Germination is best at 21°C or warmer.

Over-wintering Pelargoniums

If you’ve grown pelargoniums in your summer garden, consider trying to over-winter them for next year.  I’ve had good success with each of these methods:

• take cuttings in late summer to root for new plants,
• lift existing plants and prune back by 1/3, keeping them as a houseplant over winter (in a sunny but cooler spot). Pinch back shoots, or in early spring, you can prune back up to ¾ for leggy plants. Fertilize lightly in spring, and begin to harden off in April-May; or
• lift existing plants, shake off earth, and store in paper bags in a root cellar (mist as needed so they don’t dry out), and bring them out six weeks before the last frost to repot.

 

Pests and Diseases

Most modern pelargoniums are fairly resistant to disease and bothered by few pests in the garden. To avoid most common diseases, don’t allow leaves to remain wet (avoid overhead watering), and allow the soil to dry between watering (don’t overwater). Also, discard diseased plant parts and be cautious to purchase healthy plants. Plants may be bothered by aphids or whiteflies, so use caution when bringing them in for overwintering.

Enjoying Your Blooms

Pelargoniums are not often seen as cut flowers, but why not? Most geranium flowers are long-lasting when cut and make a great addition to arrangements. In Victorian times, they were used often and were a favourite flower of Charles Dickens, who regularly wore one in his lapel at speaking engagements.

 

References

The Complete Geranium: Cultivation, Cooking and Crafts, by Susan Conder (Clarkson N. Potter, Inc., 1992) (available at Winnipeg Public Library, lots of recipes).

Pelargonium in Wiki at https://en.wikipedia.org/wiki/Pelargonium

Gardenhistorygirl Jul 11, 2022 at https://www.gardenhistorygirl.co.uk/post/geraniums-or-pelargoniums-on-the-windowsill

“4 Easy Methods for Overwintering Geraniums”, by Marie Iannotti, in The Spruce at https://www.thespruce.com/overwintering-geraniums-1403592

Geranium Diseases, by Gary W. Moorman, Ph.D., Professor Emeritus, Pennsylvania State University at https://extension.psu.edu/geranium-diseases