Delicate, azure blue flowers bursting forth from lush, very hardy plants: These are the hardy geraniums.
The precise appeal of these often diminutive, sometimes bold charmers is tough to pin down. But it's simple from a gardener's point of view. Hardy geraniums give a lot and require very little. For instance, they grow in most climates, take shade, serve admirably as a weed-choking ground cover, and produce quantities of flowers. It is even possible to have a succession of geraniums blooming from early spring to late fall. Is it any wonder gardeners are so excited about them?
Just to be clear, I'm talking here about the plants of the genus Geranium, not those other "geraniums" -- the Pelargoniums. I apologize in advance for the name confusion, but the habit of gardeners to call those tender southern African plants "geraniums" is deeply rooted. Though both are members of the same plant family, they couldn't be more different. The Pelargoniums include common "geraniums" such as the Lady Washington geranium (P. domesticum), the ivy geranium (P. peltatum), and the scented geraniums (various species including P. capitatum and P. crispum). The effort to distinguish Pelargoniums from hardy geraniums is why you will sometimes see the latter refered to as the "true" geraniums.
There are about 500 species of geraniums world wide. They thrive on every continent -- throughout Africa, from western Europe to China, from Siberia and Alaska down the Americas to Patagonia. There are even species endemic to the Pacific Islands, including Hawaii. Some of these are available from nurseries.
Leaves of hardy geraniums are typically divided into leaflets arranged in a palm-like fashion. They range from the thumbnail-sized brown leaves of G. sessiliflorum 'Nigricans' (zones 8 to 10) to the rich mid-green dinner-plate-sized leaves of G. maderense (zones 9 to 10). You can find leaves with all sorts of quilting, veining, and blotching. Growing geraniums for their leaves alone gives valuable texture to those in-between sites that are so troublesome in the garden. Plant heights range between 5 and 36 inches.
Flowers all have five equal-sized petals. They range in size from 1/4-inch to 1-1/2 inches in diameter and can be violet, blue, pink, white, and magenta. There are no yellow or clear red geraniums. Very few flowers are "doubled" (have more than one set of petals). Although the largest flowers are not truly flamboyant and bloom is frequently sporadic rather than concentrated, there are species whose seasonal show of flowers is delightful. For example G. magnificum (zones 5 to 9) makes a five-week display of violet-blue flowers for the middle or front of a perennial border that is "magnificent" by any standard.
Hardy geraniums are incredibly tough and useful garden plants. They need little care and are pest- and disease-resistant. Most are hardy to about -20°F (zone 5). Some are much more cold tolerant, and one, G. pratense, can withstand temperatures up to -50°F (zone 2).
Most are soft-stemmed, herbaceous perennials that pass the winter season in dormancy and put on new leaves in spring.
Geraniums require well-drained, fertile, and moist soil. If you live where summer rain is infrequent or nonexistent, plan to water weekly or so. Keep in mind that geraniums are wild flowers and in most gardens do not need much coddling.
If growth is untidy, cut plants back in midseason to about 1 inch above the main stem (2 or 3 inches above the soil level). Plants will renew leaves and produce occasional flowers during the remainder of the growing season.
Growing geraniums in southern regions with high summer heat and humidity may be a challenge, but a midseason cutback of leaves will frequently renew the plant. Give G. pratense a mulch around its roots if you live where summers are very hot.
As a general rule of thumb, geraniums do best in morning sun and afternoon although some geraniums such as G. sanguineum (zones 5 to 9) and G. pratense thrive in full sun.
Propagate species types by seed, but any named varieties, such as 'Johnson's Blue', must be propagated by division of the crowns or by root cuttings. Do either in early spring.
Hardy geraniums make landscape problems a virtue. Here are my recommendations for some specific garden situations.
For shady areas, our native East Coast wildflower, G. maculatum (zones 4 to 9), is unrivaled. The best selections have inch-sized light pink flowers that fade to cream in the center.
Deep shade is always a problem for gardeners. G. nodosum (zones 5 to 9) does well in these conditions, forming small colonies of slightly shiny mid-green leaves with scattered funnel-shaped flowers in light lilac to quite dark pink.
If you would like an imposing plant that will form a clump in the shade, G. phaeum (zones 3 to 9) -- particularly the wonderful form 'Samobor' -- is a good choice. 'Samobor' has maroon blotches on its leaves and reddish maroon flowers. There is an ethereal white form, G. phaeum 'Album' that harmonizes beautifully with green and white variegated plants and also some dark forms with rich, dark chocolate-colored flowers.
A well-known, widely available hardy geranium for shade is G. endressii 'Wargrave Pink' . There are many other varieties of this species available.
The last time I counted, there were 34 named varieties of G. oxonianum (zones 5 to 9). In my opinion, the four best are: 'A.T. Johnson' (luminous pink); 'Phoebe Nobel' (dark pink); 'Winscombe' (pale pink fading to dark pink); and 'Walter's Gift' (pale pink flowers with darker veins and leaves marked with maroon). Grow any of these in shade to partial sun, and shear them to the ground in midseason to produce new leaves and new flowers.
My two favorites are varieties of G. macrorrhizum 'Ingwersen's Variety' and 'Czakor' (both hardy in zones 3 to 9). The former has aromatic leaves, which smell of balsam or pine, and pale pink flowers. 'Czakor' has strong magenta-colored flowers. Both are aggressive, weed smothering, very attractive ground covers. In mild-winter regions, they remain evergreen all year.
A less aggressive offspring of G. macrorrhizum is G. cantabrigiense (zones 4 to 9). There are two fine color forms: 'Biokovo' (white with a flush of pink) and 'Cambridge' (mid-pink with a slightly paler throat).
In Rock Gardens or Containers
If you wish to put a geranium in a specialized location, such as in a container on a porch or patio or in a rock garden, you might like to try the neat and compact G. cinereum 'Ballerina' or G. cinereum subcaulescens (zones 4 to 9). The former has inch-wide pale lavender flowers with wine-colored veins that contrast pleasantly with its ash-gray leaves. Or consider the flat little mound of brown leaves formed by the more cold-tender G. sessiliflorum 'Nigricans' (zones 8 to 10). Its flowers, however, are small, white, and in hiding. G. dalmaticum (zones 4 to 9), with nickel-sized leaves and a flush of pale pink flowers in late spring, is more showy.
Perhaps you are hoping to fill a perennial border this year or tuck a geranium in some sunny location in the garden. G. sanguineum should be on everyone's list. Particularly nice forms to try are G. sanguineum striatum with pale pink flowers and deep pink veins; 'Cedric Morris' with large, mid-green leaves and 1 1/4-inch light magenta flowers; or the beautiful G. sanguineum 'Album', which is more open and billowy in habit than the other two selections and whose flowers are pure white.
Are you crazy about blue in the garden? I've mentioned the violet-blue flowers of G. magnificum. The hybrid G. 'Spinners' (zones 4 to 9) also has deep blue flowers, but there is a hint of mauve to the color. 'Johnson's Blue' (zones 4 to 9) is a clear sky blue, and G. wallichianum 'Buxton's Variety' (zones 6 to 9) is also a light blue, but the center of each flower is white, and the leaves are faintly mottled in a lighter creamy green. G. himalayense (zones 5 to 9) has deep blue flowers that fade toward red in the center of the petals. There is double form of G. himalayense 'Birch Double', with smaller, lilac blue flowers. Perhaps you would like a paler color? G. pratense 'Mrs. Kendall Clarke' is a pale gray blue with gray veins.
If you are looking for white, G. clarkii 'Kashmir White' (zones 3 to 9) is a good choice. The flowers are quite large. They are white but with lilac veins, and there is a faint lavender wash over the petals. They look like a host of butterflies fluttering over the surface of the finely dissected leaves.
A geranium that has a very long flowering season, but, alas, is only hardy in zones 8 to 9, is G. riversleaianum 'Mavis Simpson'. Its pale pink flowers start in early spring and continue until early fall, forming a charming contrast with its gray-green leaves.
If you would like to make a dramatic statement in the garden, there are two magenta geraniums that draw the eye like a magnet. G. psilostemon (zones 5 to 9) forms, over a number of years, an imposing clump of dinner-plate-sized, mid-green leaves through which branched flowering stems bear an endless succession of inch-sized, black-eyed, magenta flowers. A more sprawling plant, and one of the finest geraniums for the perennial border, is its hybrid offspring 'Ann Folkard' (zones 5 to 9), whose purplish magenta flowers with their dark eyes form a fine contrast with chartreuse leaves. 'Ann Folkard' also blooms over a long period -- from spring to fall.
Growing hardy geraniums is a dangerous passion. There are so many wonderful plants to choose from. They are becoming widely available in the United States and Canada though mail-order nurseries, and most gardeners find it impossible to stop at only one.
Robin Parer owns and operates Geraniaceae Nursery in Kentfield, California.
Photography by Mike MacCaskey/National Gardening Association
Article published on June 23, 2008.