Soapworts - the Genus Saponaria
During the last two weeks I introduced you to the campions and catchflies, members of the genus Lychnis and Silene. These are both members of the Pink Family, Caryophyllaceae. This week I'll describe another group of close relatives: the soapworts, also known as Saponaria. As previously mentioned, the genus Lychnis and Silene are separated based on subtle floral differences. The genus Lychnis has 5 styles and a capsule that opens with 5 teeth. Silene have 3 styles and capsules that open with 6 teeth. The genus Saponaria has flowers very similar to the previous two genera but their flowers have 2 styles and capsules that open with 4 teeth. Again, as gardeners, we are more interested in how they may be incorporated into our gardens.
Certainly, compared to Lychnis and Silene, there are far fewer garden worthy soapworts. There are about 20 species in total, all hailing from Europe and neighboring western Asia. Like the campions and catchflies, soapworts may inhabit meadows, woodlands or alpine regions. However, unlike their close relatives, soapworts are rather long-lived perennials. Most prefer full sun and well-drained soil but the common soapwort, S. officinalis, will tolerate some shade. Like the campions and catchflies, pink is the dominant colour although white and even yellow forms exist. Several are highly fragrant, a feature not so common among Silene and Lychnis.
The common name ‘soapwort' comes from the Latin sapo, meaning soap. The leaves of common soapwort or bouncing bet, S. officinalis, have been used since medieval times as a source for soap. Today, museums still utilize soap from this plant to clean delicate fabrics. This highly fragrant species has long been a popular subject for the cottage garden. The double form is particularly attractive. Plants spread fairly quickly by underground rhizomes and can become a bit of a pest. Use in areas where it can be contained and promptly deadhead to help reduce the spread of their seedlings. Common soapwort is the tallest Saponaria, reaching 60-90 cm. The stems can be a little weak so light support, especially for the double-flowered form, is recommended. Full sun and evenly moist soil will result in the strongest plants but they will tolerate some shade. They can survive into zone 2b.
Above are images of S. officinalis, the wild form, double white and double pink.
The other common soapwort is the creeping soapwort, S. ocymoides. This trailing perennial is easy to grow from seed and will even self-seed to a degree. Masses of pink (more rarely reddish or white) flowers are produced in mid-late spring. This species is ideal for cascading over retaining walls, slopes or in the rock garden. This one is also super hardy, rated for zone 2b.
Details of S. ocymoides
Less commonly seen is the straw-yellow flowered species, S. bellidifolia. This rather tender species (zone 7) has 50 cm stems topped with a tight cluster of flowers. This one also benefits from light staking and may be better used in a wildflower setting.
The remaining species are all rock garden plants and more difficult to find (try specialty alpine growers). They require full sun and well-drained soil and prefer some protection from excess winter-wet. They are also less hardy than the previous species, rated for zones 5 or warmer. Saponaria caespitosa (zone 5) is a tufted, tap-rooted species that produces wiry stems, 15 cm in length, which end in a cluster of pink flowers. This species blooms in late summer, useful for extended the blooming season in the rockery. Also late-blooming is S. pamphylica (zone 5). This tufted species has attractive blue-grey foliage and fairly stiff, upright stems to 15 cm topped with a few bright pink flowers. Very choice is S. haussknechtii (zone 7) which produces a tight mat of bluish foliage and quite large pink flowers in summer. Saponaria pumilio (zone 5) is another taprooted alpine species with somewhat fleshy leaves. It has large, almost stemless, pink flowers in summer but is challenging to grow as they are sensitive to excess winter-wet. Looking similar but easier to cultivate is the hybrid S. x 'Olivana' (zone 5), which is a combination of S. ocymoides, S. pumilio and S. caespitosa. Finally there is S. lutea (zone 6). This tufted alpine has arching 10 cm stems that end in a cluster of straw-yellow flowers with contrasting purple stamens.
Above are images of S. X Olivana and S. lutea
While the soapworts offer less variety than the campions and catchflies, they do have some rather attractive members that are well worth seeking out.
I would like to thank the following people for the sue of their photos: Isabelle Rey (S. lutea), chaosmosis (S. officinalis double white) and poppysue (S. officinalis wild form)
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