Silvery Erodiums and Their Kin

Erodium chrysanthum

Erodium chrysanthum. Author’s photographs

Consider silver tea sets, silver threads among the gold, and silver anniversaries—comfortable reminders of wealth, of age, and of the passage of time.

Silver is not as flashy as gold. It might be described as a milestone along the way to gold if you are counting anniversaries—an acknowledgment of staying power, of commitment, and of genuine worth. There is nothing extreme about silver, rather something useful and solid. Gold has been man’s obsession for thousands of years and the amassing of it an indicator of wealth, success, and power. High drama and great disaster have ensued and fortunes have been gained and lost. An interest in silver somehow seems less extreme.

When Mrs Desmond Underwood’s book Grey and Silver Plants appeared in 1971, her publisher, Collins, claimed that it was the first book of its kind on the subject. Over the ensuing thirty years, however, mediterranean gardens and planting schemes for them have included many silver- and gray-leafed plants, and silver-leafed plants have been featured in many perennial gardening books. Today, gardens of silver foliage are up-to-date and fashionable, as well as being environmentally sensitive, particularly in the perpetually drought-menaced regions of the Western United States. Plants for mediterranean-style gardens have the advantage of being tolerant of high levels of summer sun as well as minimal water once established.

We associate silver-leafed plants with hot, dry climates. Just as houses in hot climates are often painted white to reflect the intense light and keep interiors cool, so plants protect themselves against heat and light by a covering of gray and silver hairs on leaf surfaces. These hairs, often dense, reflect light and protect the stomata that release water from leaf surfaces. In some cases, plants hold their silver leaves erect so that the leaf surface is less directly exposed to the sun (compared to leaves that lie flat). Plants with silver foliage generally occur in harsh climates along dry, hot seacoasts, in deserts, and in alpine areas where light intensity is high and the potential for water loss through evaporation is great. Rainfall is frequently low or moisture is available only in the form of snow or fog. Hairs can trap moisture that may occur in the form of fog, mist, or occasional brief showers. Strong winds may occur, droughts may be frequent, and there may be extremes of both heat and cold.

Silver-leafed plants are not always easy to cultivate. The very conditions that challenge their survival in the wild often need to be specially duplicated in gardens. Situations that replicate little to no summer water may be possible by grouping plants with similar needs together. Alkaline soils, often a feature of deserts and mountainous regions, can be specially mixed and plants put in containers or grouped in areas such as rock gardens. High levels of light can be achieved by locating silver-leafed plant collections in areas with bright light and highly reflective surfaces. It is not enough to merely put silver-leafed plants in the garden with no regard for their needs and then to hope for the best.

Plants with silvery foliage in the geranium family (Geraniaceae) are found in the Mediterranean Basin, in the mediterranean climate region of Southern Africa, in South America on the altiplano of Peru and Venezuela, and on the Hawaiian Islands of Maui and Hawaii. These silvery foliaged plants occur in four genera in the family: Geranium, Erodium, Pelargonium, and Monsonia. Within each of these genera are a few odd but wonderful examples of plants with silver leaves that are adapted to life at the extremes. It is never wise to declare to a group of gardeners that plants are difficult to grow. Some will take that as a challenge. However, growing most of the following plants demands a bit of skill as well as some luck.

Erodiums

Erodiums are the Cinderellas of the geranium family: beautiful, worthy, and neglected, although usually easy to propagate and cultivate. Erodium reichardii (syn. E. chamaedryoides) is widely available from retail nurseries in the West for use as a ground cover; small collections of a few species or hybrids of unusual erodiums are sometimes found in collectors’ rock gardens. However, there are many excellent plants that are generally unavailable, neglected, or ignored. Although their cold hardiness can be a problem in the central and eastern parts of the United States, erodiums will grow successfully in most of the West Coast states. Many erodium grow naturally in calcareous soils, and respond well to the addition of dolomite, oyster grit, or even concrete chips to potting soils that are neutral to somewhat acidic. As with many other genera, only a few members of the genus Erodium have silver leaves.

Erodium absinthioides. Author’s photographs

Erodium absinthioides

Erodium absinthioides comes from Albania, Armenia, the Balkans, Greece, and Turkey. Varying from gray green to silvery, its leaves are bipinnately compound and about one and a half to two inches long. Plants form mounds about eight inches high by twenty inches wide, although part of the width is taken up by the annual flowering stems. Plants with the most silvery leaves seem to be the most compact. This species is dioecious (producing male and female flowers on separate plants). Flowers on the silver form are light pink becoming paler towards the base of the petals, six-tenths of an inch in diameter, and form a pleasing contrast against the foliage. Plants looks splendid draped over a rock wall. ‘Genoa’ is a selection noted for its ivory flowers with a pink flush and colorless veins. Propagation is by stem cuttings in early spring.

Flowers of Erodium chrysanthum

Flowers of Erodium chrysanthum

Erodium chrysanthum comes from mountainous areas of Greece and Albania. Plants produce tufts of silvery, pinnately divided leaves about one and a half inches long and can form substantial mounds up to eight inches high by two feet wide after a few years. This species is also dioecious and all selections of the species currently in cultivation (excluding its look-alike hybrid E. x lindavicum) appear to be male. Flowers are pale yellow and slightly under an inch in diameter; flowering can be profuse in late spring and early summer. This species tolerates high summer temperatures and, when hardened off before winter, is cold tolerant to USDA zone 4/5. Plants are handsome even when not in flower, attractive in containers, rock gardens, and at the top of low rock walls.

Erodium guicciardii originates in the mountains of Northern Greece, Yugoslavia, Macedonia, and southern Albania. Its leaves are bipinnately compound, four and a half inches long, grayish silver in color, and deeply divided. Flowers appear in umbels of two to seven flowers each and are light pink with faint deep pink veins, three-fourths of an inch in diameter, and carried on long flowering stems. This is wonderfully garden worthy, forming a largish mound about twelve inches high by twenty inches wide. Propagation by stem cuttings is easy in early spring. This is another dioecious species and seed is difficult to obtain.

Erodium x kolbianum ‘Natasha’

Erodium x kolbianum ‘Natasha’

Erodium x kolbianum ‘Natasha’, a hybrid between E. ruprestre and E. glandulosum, has silver leaves that are deeply dissected and about three inches long. Its flowers are presented in umbels and are the palest pink, about three-fourths of an inch in diameter, with dramatic purple and silver blotches and veins on the two upper petals. Flowers with several extra petals are occasionally produced. In the rock garden, plants form dense mounds up to six inches high and eighteen inches wide. Highly floriferous, ‘Natasha’ is also attractive in a container. Propagation is by stem cuttings in the early spring.

Erodium ruprestre comes from the massif of Montserrat, west of Barcelona in northeastern Spain. Its pinnately divided leaves are silver above and green beneath. It is a compact mounding plant about eight inches high by twelve inches wide. The flowers are pale pink without blotches but with darker pink veins, particularly noticeable on the two upper petals. Like its offspring, E. x kolbianum ‘Natasha’, E. ruprestre flowers prolifically over quite a long period in late spring and summer. Stem cuttings taken in early spring seem the easiest way to propagate this species.

The main problem for growers of erodiums is stem rot brought on by excessive moisture when the plants are not in active growth, usually during the winter months; leaves yellow, tips wilt and dying stems follow. Encircling plants with grit or sand usually helps, as it prevents mud-splash onto sensitive stems and leaves. A cool greenhouse may be another option, although there are fewer problems in the garden if drainage is good. Gophers and voles are sometimes attracted to erodium roots; the first sign of animal damage is a plant that has toppled over.

Silvery foliage of Geranium cuneatum subsp. tridens on Haleakala, Maui

Silvery foliage of Geranium cuneatum subsp. tridens on Haleakala, Maui

Geraniums

Tourists driving up the road to the Visitors Center of Haleakala National Park on the island of Maui—if they are looking at the vegetation and not the breathtaking view—will see the sparkle from hundreds of silver-foliaged shrubs within the predominantly olive and gray green vegetation. Few people would guess that the silver shrub is a geranium (Geranium cuneatum subsp. tridens) discovered as recently as 1976. Located in decaying lava flows, exposed to intense solar radiation with no shelter from wind, and experiencing wide swings in temperature, G. cuneatum flourishes. It ranges from three to five feet tall and may spread to five feet wide. The stems are gray and twiggy, sporting silver leaves about one inch long with parallel veins and three conspicuous teeth at the tip. The flowers are creamy white and about three-fourths of an inch wide. Occasional shrubs have flowers with distinctive red veins. The leaves have been described as resembling the wings of a insect; certainly, geranium would be the last thing on your mind until you saw the beak-like fruit, which is characteristic of the geranium family. Seeds of G. cuneatum germinate readily, but plants have been hard to maintain in cultivation. Could it be that a decaying high altitude volcano and daily immersion in cool fog is hard to duplicate in the average garden? Enjoy it where it lives; it is a fascinating plant.

Geranium hanaense, discovered even more recently (1988), is a low shrubby mound, also with silvery leaves but, unlike the last, is found in a protected site in the upper Hana Rainforest in East Maui. There is much speculation as to why it might be now living in a bog, like a fallen lady, when it seems that it should be in a drier area. It does not appear to be in cultivation.

Geranium argenteum is an alpine plant from the southern French Alps, Apennines, Slovenian Alps, and northeastern Italy, found on limestone, dolomite, and igneous rock. It is an herbaceous perennial in the form of a rosette with rounded, silvery, silky leaves that are deeply seven lobed. Each lobe is divided into three parts and the lobes do not lie flat, a distinctive characteristic. Deep pink, pale pink, and white flowers appear in this species and are about one and a half inches in width. In time the plant will make a mound of about eight inches high by twelve inches wide. The main requirement for growing G. argenteum successfully is excellent drainage and a summer that is not too hot. Although it is a very attractive plant for a rock garden or container, it is continually being lost in cultivation. One can find, however, the occasional smug gardener who grows it to perfection. It is an ideal plant for an alpine house with an obsessively attentive custodian. Rock garden societies occasionally offer seed of this species.

Geranium harveyi creating a river of silver in the Entry Borders at Strybing Arboretum

Geranium harveyi creating a river of silver in the Entry Borders at Strybing Arboretum

Geranium harveyi creates the illusion of a molten river of silver in the garden. It forms a woody stemmed mound that elongates to about twelve inches high by two feet wide. Small, lobed and toothed leaves are about one inch wide and long and covered with dense silvery hairs. The light magenta flowers are about three-fourths of an inch in diameter. Flowering is not profuse, but the leaves are the outstanding feature of this plant. It seeds readily in some gardens, but is never a nuisance. It should be given a haircut in early summer to keep the mound neat and tidy. It comes from the Transkei and Cape Province in South Africa. Winter hardiness may be a problem beyond USDA zone 7. Propagation is by stem cuttings in early spring.

Pelargoniums

There are only a few pelargoniums with silvery leaves. One of the most markedly silver is Pelargonium sericifolium, a little branching subshrub, eight inches by eleven inches, with deeply divided palmate leaves covered with a silver indumentum of long, silky, glossy hairs. The flowers are intense pinkish purple. This species comes from the extreme northwestern Cape Provence, in the Succulent Karoo of South Africa. In different areas, it can be found on granite, gneiss, and deep red sand. Rainfall throughout its range is only four to eight inches a year, but there are early morning mists. Winters are mild and summers exceedingly hot. Stem cuttings root readily and seeds germinate easily, although they are not easy to find in seed lists. Plants prefer full sun and limited water, best in a dry greenhouse with strong light during the winter.

Sarcocaulon

The last genus in the family, Monsonia, does not include any species with truly silvery foliage, as far as is known. Recently, botanists have considered making the genus Sarcocaulon a sub-group of the genus Monsonia. Sarcocaulon peniculinum comes the closest to our silvery leafed ideal. It is the rarest of all South African sarcocaulons. Growing in truly harsh conditions in southwest Africa between the Orange River and Rosh Pinah (probably the only town to have sarcocaulon growing on its golf course, according to RO Moffett), it is found in shallow clay depressions in rocks in mountainous deserts; it does not even have the advantage of fog for moisture, but exists on extremely sparse and occasional rainfall. It is leafless for most of the year, leaves and flowers appearing only after rain. It is a prostrate, dwarf shrublet, about three inches high by seven inches wide, with only two swollen horizontal branches. The upper surfaces of these branches have small, deeply divided, densely hairy, silver leaves. Flowers are moderately large, up to one and a half inches across, and pale pink to deep pink. Seeds have been difficult to obtain, although the seed of most species germinate readily. Overwatering is the main cause of death for sarcocaulons in gardens.

When the world contains so many plants with silvery leaves that are easy to cultivate, it might be asked why we would bother with the silver-leafed Geraniaceae? Lives there a gardener who is not challenged by a difficult plant? This is a remarkably diverse family, and some of its members survive in dramatically harsh conditions. The fact that plants, related to the ubiquitous red potted geranium, are surviving on the tops of high mountains and in the most rigorous deserts should give us a greater appreciation of this remarkable family. Along the way, the Geraniaceae will provide plant collectors and growers with yet another fascinating group of plants to acquire, cultivate, and enjoy.


A Resource Guide to Erodium and Their Kin

The Geraniaceae Group is a great resource for seed of unusual plants in the family. Membership is ten pounds sterling per year and includes an annual seed list and a quarterly magazine. Contact the Membership Secretary: Ms Penny Clifton, 9 Waingate Bridge Cottages, Haverigg, Cumbria LA18 4NF England.

Plants and Seeds

Silverhill Seeds (native South African species), PO Box 53108, Kenilworth, 7745, South Africa. www.silverhillseeds.co.za

Geraniaceae Nursery, 122 Hillcrest Avenue, Kentfield, CA 94904, 415/461-4168. www.geraniaceae.com

For Further Reading

Craib, Charles. The Sarcocaulons of Southem Africa. Hystrix Natural History and Cultivation Series, Vol. 1 No. 3, May 1995.

Moffett, RO. The Genus Sarcocaulon. Bothalia 12, 4 (1979):581-613

Van der Walt, JJA and PJ Vorster. Pelargoniums of Southern Africa, Vol. 2. Cape Town and Johannesburg: Juta, 1981.

Yeo, Peter F. Hardy Geraniums. Portland, Ore: Timber Press, 1985.