Hardy Geraniums are in general very serviceable and these four have been very useful and successful for me. They are tolerant of diverse and adverse conditions and are especially useful in dreaded dry shade.
Geranium macrorrhizum has big (macro) rhizomes and thick rooting stems by which it can spread to 12”-18”+ wide, growing to about a foot high and making a thick, weed-competing ground cover. If well fed and watered, this plant could dominate an area. The foliage is very aromatic and sticky and is medicinal, as is the root. The flowers can be pink, dull magenta or white. The plant is variable in form and tolerance to drought. It has done well in my xeriscape, occasionally suffering in the worst dry, but then coming back strong each spring.
There are many forms: Album has white flowers, ‘Bevan’s Variety’ has deep red sepals and deep magenta petals, and ‘Ingwersen’s Variety’ has pale pink flowers, pale green foliage and has excellent form. I was given a strongly aromatic variety with beautiful pink flowers that was brought from Bulgaria.
Geranium dalmaticum is from Yugoslavia. It is said to be similar to G. macrorrhizum but smaller in all ways. It is also rhizomatous, but only gets 4”-6” tall and 12” in diameter. The small dark green leaves are deeply cut and aromatic, turning to a vibrant red fall color. The flowers are a clear, shell pink. It is good in sum or part shade.
Geranium cantebrigiense is a hybrid of G. macrorrhizum and G. dalmaticum. It was bred at Cambridge University and also occurs naturally in the wild. It forms mats of glossy aromatic foliage, intermediate between its parents. It is very strong and vigorous with rich pink-violet flowers, making a dense ground cover. This one has been very tough in my xeriscape, lush and beautiful where many others would have died. It would be one of the best for dry shade. Because it sets little seed, it blooms a very long time. Its fall color is wine red.
A variant of G. cantebrigiense, found in the Biokovo Mountains of Yugoslavia, is named ‘Biokovo’. It forms a shorter, supposedly looser mat with white flowers tinged pink. It also has great red fall color.