Soapwort Plant Profile

close up view of the flowers on a soapwort (Saponaria officinalis) plant

Nigel Hicks/Dorling Kindersley/Getty Images

Soapwort (Saponaria officinalis) is a multipurpose perennial herb that has a place in any herb garden. As its name suggests, soapwort long has been used to make detergent and soap due to the saponins of its roots and leaves that create bubbles. But the plant also has ornamental value.

The herb grows erect with green, leafy stems without side branches. It readily flowers throughout the summer months. Forming in clusters, its blooms are approximately 1 inch in diameter with five petals, and they give off a sweet, floral scent that's somewhat reminiscent of cloves.

Soapwort is a very fast-growing plant that readily self-seeds. It grows successfully no matter when it is planted. Soapwort is regarded as invasive in many regions, so take care to supervise its spread if you choose to plant it in your garden. The plant was introduced to North America by European settlers, and has naturalized across the U.S. as a roadside weed.

Botanical Name Saponaria officinalis
Common Name Soapwort, common soapwort, bouncing bet, crow soap, wild sweet William, soapweed
Plant Type Herbaceous perennial herb
Mature Size 1 to 3 feet tall; similar spread
Sun Exposure Full sun to part shade
Soil Type Dry to medium-moisture, well-drained soil
Soil pH 5 to 7 (acidic to neutral)
Bloom Time May to September
Flower Color Pink, white
Hardiness Zones 3 to 9 (USDA)
Native Area Europe, Asia

How to Grow Soapwort

Soapwort is a vigorously growing plant that requires little maintenance. In fact, the most effort you put into the plant might be to stop it from spreading all throughout your garden. The herb isn't very fussy about where it's planted, though it would prefer a sunny spot with well-draining soil.

Soapwort has seen various applications throughout history. The Romans were said to use the herb as a water softener. Farmers would make soap out of it to bathe sheep before shearing, as well as to clean wool. And colonists to the United States brought the plant with them from Europe as a soap substitute.

When roughly chopped and then boiled in some water, soapwort creates a cleanser that can effectively remove oils, but is so mild that museums sometimes even use it to wash delicate textiles. At home, you can use it to launder fragile fabrics, such as lace. Soapwort also is gentle on sensitive or irritated skin. People are known to boil its roots to make a wash for itchy skin, acne, and psoriasis. And boiling its leaves, stems, and roots can create a sudsy hair-washing solution.

Light

If you want a dense plant with plenty of blooms, grow soapwort in full sun. It also can tolerate a bit of shade, though the plant might not be as lush.

Soil

Soapwort is easy to grow in most soil varieties, as long as the soil is well-draining. This means the herb can become invasive in some gardens. When planted in moist, rich soil, soapwort might grow uncontrollably and take on a disheveled and floppy appearance. Soil that is slightly rockier can help to temper its growth. 

Water

The herb prefers consistent moisture, but it can tolerate some drought. During a prolonged dry spell, be sure to give soapwort regular watering.

Temperature and Humidity

Soapwort is a hardy plant that thrives in the full range of conditions found in its growth zones. It prefers a minimum of 130 frost-free days per year, though it can survive winter temperatures well below freezing. For cold climates, a layer of mulch can help to protect the plant over the winter. This plant grows equally well in arid climates as it does in humid regions.

Fertilizer

Once established, soapwort plants can grow for years with little assistance. If you have poor soil, consider fertilizing once per year in the spring with an all-purpose fertilizer. But feed lightly, as too many nutrients can damage the plant.

Pruning

Deadhead flowers during its blooming period to promote more flowering. Once the plant is finished blooming in the fall, cut it back by about half, especially if it experienced robust summertime growth. This helps to keep soapwort neat and healthy, and it limits invasive spreading.

Propagating Soapwort

Soapwort spreads with creeping underground rhizomes and easily reseeds itself. If you wish to plant it in different locations, it’s easy to take divisions from an established soapwort plant with the roots attached. This should be done in the spring or fall, though divisions can be successful at any point during the growing season as long as they're kept moist. Soapwort is typically not ideal for planting in pots due to its growth habit.

Harvesting

Pick flowers, leaves, and stems as needed. Harvest soapwort roots in the fall.

Toxicity of Soapwort

Although soapwort has some usage in the culinary world, including creating foam on beer and brewing tea for throat issues, it's best not to eat it. The herb is toxic in high doses and can cause vomiting, diarrhea, and other health problems. The saponins in soapwort also are harmful to fish, so it's not a good idea to plant it next to any bodies of water where aquatic life resides.

Landscape Uses

Soapwort is suitable for ground cover, edging, walls, and more, and it works well for living roofs. It is a good choice for gardeners seeking to attract pollinators. Given its extreme vigor, it is perhaps best suited for cottage gardens and other areas where its urge to spread and naturalize is not a serious flaw.