He knew it well, though it was seldom to be found even in the shady places in Wales where he had occasionally seen it. He knew of no place here in England where it had ever, to his knowledge, been discovered. When he wanted seed to make powders or infusions against colic or stone, he had to be content with the poor relatives of this rarity. Now what, he wondered, viewing its very late and now somewhat jaded flowers, is a bunch of the blue creeping gromwell doing in these parts? Certainly Domville had not had it when he left the abbey.
- Ellis Peters, The Leper of St. Giles, 1995
Just so did creeping gromwell provide the clue that would lead Brother Cadfael to solve the mystery of the murder of Huon de Domville. Being an herbalist, Cadfael noticed the posy and that it was out of place. Certainly, you understand because, as a gardener, you notice plants before you see much else.
But there is another mystery. What was the plant that Brother Cadfael spied? Culpeper noted the long-established medicinal value of gromwell in his Complete Herbal. Cadfael was drawn into this mystery in the first place because he was out and about looking to restore his supply of herbs. Was it a Lithospermum or a Lithodora? We may never know which; besides Cadfael is a fictitious character.
The Brother Cadfael Chronicles are set between the years 1135 and 1150. But the botanical name, Lithospermum, wasn't bestowed until around 1750 or so by Linnaeus. The genus, Lithodora, was described and separated from Lithospermum around 1844. Both have been commonly called "gromwell", in some form. But we do know that the flowers of Cadfael's gromwell were "heavenly blue", so that might help to narrow it down for you plant sleuths.
Of the two genera, Lithodora is more important horticulturally, so I'll focus on that. But I must note at this point that some of the plants within the genera are still called Lithospermum synonymously.
Lithodora (pronounced "lith-o-DOR-ah") means "stone gift", but there seems to be no record why it was named so. The stone might refer to the hard, nut-like seed the plant produces, but it might as well refer to the topography or soil type of some native habitat. Lithodora diffusa, for example, is native to southern Europe (Spain and Portugal) and a couple of areas near the southern Mediterranean.
Most species grow fewer than 8 inches in height, spreading perhaps to 18 inches. Foliage is lanceolate or linear, resembling rosemary but with hairy surfaces. Flower colors range from blue to white. (Lithospermum flowers are often yellow.) They tend to be drought-tolerant, making them ideal for xeriscaping. Acid soil is usually preferred. They aren't particularly cold hardy or heat tolerant, usually doing best in USDA climate zones 5 or 6 through 7 or 8.
Lithodora diffusa thrives in a broader climate range, usually from 5 through 9, which undoubtedly contributes to its greater popularity. Flowers appear in late spring and summer. It requires well-drained soil in full sun to partial shade. Soil pH should range between 5.6 to 6.5. Lithodora is deer resistant.
When you've chosen your planting site, take a soil sample to your nearby Cooperative Extension Service office for analysis. Follow soil test recommendations, making any amendments as needed. Remove all traces of weeds. Apply an appropriate herbicide. I prefer glyphosate. If your soil is not friable, cultivate to 8 inches deep. Water your plants in the pot before installing. Space them 12 inches to 15 inches apart. Surrounding soil should come to the top level of the root ball; don't bury it. Water again after planting.
Lithodora diffusa is great for perennial borders, ground cover, containers, hanging baskets, herb gardens, and perhaps as a lawn substitute if foot-traffic is light. It's also ideal for tucking into stone walls. Consider planting a theme garden; perhaps a medieval garden, medicinal garden, or a literary garden to celebrate plants made famous in poetry and prose. If you are looking for a plant that will do all that, and if you garden in an appropriate climate zone, plant Lithodora. Your mystery is solved.
Return to Lithodora at goGardenNow.com.