How to Plant and Grow Soapwort

With its profusion of blooms and vigorous growth habit, this old-world perennial has made a home in herb and cottage gardens everywhere.  Soapwort (Saponaria spp.) is prized for its long-lasting blooms. Available in many shades of pink and white, these little flowers are reminiscent of phlox blossoms. They bloom freely for months, usually starting in late spring, with some varieties carrying on well into the fall months. The flowers have a lovely sweet fragrance, especially in the cooler evening hours.

Soapwort first became popular as an ingredient in a gentle soap solution because of its high levels of saponins. All parts of the soapwort plant contain saponins, which are highly toxic to fish, so avoid planting it near ponds and water gardens. It is also mildly toxic to humans and livestock.

Where to Plant Soapwort

Plant soapwort in a full or partial sun location. An area with afternoon shade is ideal in extremely hot climates. Lean, well-draining garden soil is best, although soapwort can grow in rocky and sandy soils.

Low-growing types look good spilling over walls in rock gardens, troughs, and containers. Taller varieties work well mixed with other tough perennials.

How and When to Plant Soapwort

The best way to add soapwort to the garden is to plant seeds. Direct sow soapwort seeds in a prepared bed in early spring immediately after the last frost. The seeds benefit from a period of cold before they germinate. Don't amend the soil to make it rich; the plant does better in lean soil. However, if the soil lacks good drainage, amend it with compost. It needs to be well-draining. Press the seeds lightly into the soil but don't cover them. When they germinate, thin them to 1 foot apart.

You can sow soapwort seeds in a container during the winter for transplants to set out in the garden in spring. Don't cover the seeds with soil; just press them in, and place the container in a cool area with bright light.

You might be able to purchase nursery-grown plants that go into the ground after the last frost in spring. Dig holes in a prepared bed just large enough for the transplants and space them 1 foot apart. Water them well.

Soapwort Care Tips

Soapwort is easy to grow and requires little hands-on care after it is established.

Light

Plant soapworts in full sun to encourage compact growth and maximize blooming.

Soil and Water

Soapwort can thrive in rocky, sandy soils, but for best results, plant it in lean, well-drained soils. If the soil is too rich, the plant can become overly lush and floppy, taking on a messy look. Lean soil reduces unwanted spreading.

When it is newly transplanted, soapwort needs frequent watering, but after it is established, the drought-tolerant plant needs watering once a week during the summer for the best bloom production.

Temperature and Humidity

Soapwort is exceptionally cold-hardy and tolerates freezing temperatures as long as it receives at least 120 frost-free days in a year. In extremely cold areas, apply a layer of mulch around the plants in winter to protect the roots.

Soapwort doesn't grow as well in hot, humid environments.

Fertilizer

Soapwort can go years without fertilizer, but if you think your plant needs it, apply a balanced, slow-release granular organic fertilizer, following the directions on the product for the correct quantity, or spread homemade compost around the base of the plant. Don't overfertilize; the plant grows best in lean conditions.

Pruning

In the fall, after the plant has stopped blooming, cut it back for a tidier look and to minimize reseeding. Other than that, deadhead the spent blooms during the growing season to promote additional blooms.

Potting and Repotting Soapwort

Soapwort is not ideal for planting in a container because it is a low-growing, spreading plant, but if you want to grow soapwort in an area where it is potentially invasive, grow it in a container to limit its invasive tendencies. The container must provide excellent drainage; the plant can't stand soggy roots. Cut the plant back by half when it is dormant in winter, and there will be no need to repot.

Pests and Problems

The bitter-tasting, toxic leaves of soapwort don't attract animals—including deer and rabbits—or insects, and the plant is resistant to most diseases.

How to Propagate Soapwort

Soapwort can be propagated through seeds, divisions, and stem cuttings:

Seeds: Soapwort self-seeds prolifically. Save a few blooms after you deadhead them and put them in a warm, dry place to dry out. Break them open to harvest the seeds. Sow the seeds on top of a prepared garden bed in early spring by pressing them into the soil and not covering them. You can also sow seeds indoors in winter for transplants for the following spring. Germination takes about three weeks.

Divisions: Soapwort spreads itself by underground rhizomes. Dig up an existing plant and separate it into several divisions using your hands or a sharp spade, being careful not to damage the rhizomes. Replant the divisions immediately into a prepared garden bed and water them. Spring or fall is the best time of year for soapwort divisions.

Cuttings: Take stem cuttings from soapwort in late fall. Remove all but the topmost leaves and dip the stem in a rooting hormone powder. Plant the cutting in a container with sterile planting mix and cover the container with a clear plastic bag to retain humidity. Put the container in a cool area with bright light. When new growth appears, the stem has rooted. After a robust root system has developed, the cutting can be transplanted to the garden.

Types of Soapwort

Bouncing Bet

Saponaria officinalis comes in single and double forms slightly larger than a dime, in white, red, or rosy pink. The flowers are held in loose clusters on sturdy 2-foot stems with knots at the nodes. Some forms have variegated foliage. Zones 3-9

Rock Soapwort

Saponaria ocymoides develops mats of bright green leaves and is covered with sprays of small bright pink flowers in late spring. It grows 6-9 inches tall and is hardy in Zones 4-8.

Soapwort Companion Plants

Veronica

Easy and undemanding, veronicas catch the eye in sunny gardens over many months. Some have mats with loose clusters of saucer-shaped flowers, while others group their star or tubular flowers into erect tight spikes. A few veronicas bring elusive blue to the garden, but more often, the flowers are purplish or violet blue, rosy pink, or white. Provide full sun and average well-drained soil. Regular deadheading extends bloom time.

Balloon Flower

The inflated buds of balloon flowers are fun to pop, and they make excellent cut flowers. Cut them in the bud stage, and sear the base of the stems to prevent the milky sap from seeping out and fouling the water. Most commonly available in blue-violet, balloon flowers also come in pink and white, as well as shorter forms that are better suited for rock gardens and containers. In fall, the foliage of balloon flower turns clear gold; don't cut the plant down too early or you'll miss the show. They tolerate light shade but not wet feet or drought.

Blazing Star

Valued for its unusual flower shape, blazing star sends up erect spires of usually magenta, sometimes white flowers. Emerging from grasslike foliage, the blooms make a dramatic statement in flower gardens with other perennials, annuals, or shrubs. Well-drained but moisture-retentive soil is a must for this prairie native.

Helenium

Long-blooming helenium lights up the late-season garden with showy daisy flowers in brilliant yellows, browns, and mahogany, centered with prominent yellow or brown discs. Many of the best cultivars are hybrids. All are excellent for cutting. Deadhead to extend bloom time and divide the clumps every couple of years to ensure vigor.