Tharp's spiderwort (Tradescantia tharpii)
Tharp's spiderwort (Tradescantia tharpii) is a compact perennial for deep shade, offering rose to purple blooms from May to July.
Complete Plant Information
Overview
Tharp’s spiderwort, or Tradescantia tharpii, is a highly valuable, compact herbaceous perennial prized for its adaptation to deeply shaded garden environments. This native plant offers contrasting rose to purple flowers atop tidy foliage, providing essential late spring and early summer color where many other perennials struggle. It forms attractive clumps perfect for naturalizing in woodland settings or stabilizing moist banks.
This particular subspecies, Tradescantia tharpii, is known for remaining relatively neat compared to some of its sprawling relatives. While individual flowers last only a day, the succession of bloom stretches the display, offering consistent textural interest with its strap-like green leaves throughout the growing season. Gardeners appreciate Tharp’s spiderwort for its resilience in medium-moisture, shady spots.
Native to the prairies and woodlands of Texas, Missouri, Kansas, and Oklahoma, it brings a touch of native ecology to the landscape. Whether used in rock gardens or naturalized drifts, Tradescantia tharpii reliably returns year after year in adaptable hardiness zones, making it a dependable structural plant for difficult shady corners.
Fast Facts
- Plant Family: Commelinaceae
- Plant Type: Herbaceous perennial
- Native Range: Texas, Missouri, Kansas, Oklahoma
- Hardiness Zones: USDA Zones 4-9
- Size at Maturity:
- Height: 0.5-1 ft
- Spread: 0.5-1 ft
- Bloom Time: May to July
- Bloom Description: Rose to purple
- Sun Exposure: Part shade to full shade
- Water Needs: Medium
- Maintenance Level: Medium
How to Grow
Plant Tradescantia tharpii during the spring or fall, focusing on establishing the roots before intense summer heat or winter cold arrives. The ideal location offers protection from the harsh afternoon sun, thriving best in part shade to full shade conditions. Soil preparation is key to success; ensure the planting medium is acidic, sandy, and well-drained loam. While Tharp’s spiderwort generally prefers consistently moist soils, it shows good tolerance for slightly drier sites once established.
Water regularly when establishing the plant, providing a medium amount of moisture consistently throughout the season. Fertilizing is rarely necessary if the soil is rich enough, as this plant adapted to lean, native soils. To maximize flower production, deadhead each spent flower cluster immediately after all buds within that cluster have opened. This practice encourages rebloom later in the season.
After the plants set seed in the summer, you may notice the foliage looking tired or entering a period of semi-dormancy. This is the ideal time to cut the stems back hard, almost to the ground. This vigorous pruning promotes a flush of attractive new foliage growth and often results in a second round of bloom extending into the late summer or fall. Divide overcrowded clumps of Tradescantia tharpii every few years during the spring to keep the plants vigorous; they will naturally naturalize and spread slowly over time.
Landscape Uses
Tradescantia tharpii excels in applications where reliable, low-growing color is needed beneath deciduous trees or on woodland edges. Its suitability for naturalizing shines when allowed to spread gently along moist areas adjacent to streams, ponds, or marshy borders, softening hardscapes beautifully. Use Tharp’s spiderwort to fill the middle or front layers of shade borders, pairing it with later-blooming shade lovers like hostas or ferns to ensure continuous seasonal interest.
For structured gardens, incorporate this clump-forming perennial into rock gardens where the sharp drainage mimics its native habitat. The contrasting strap-like foliage serves as an excellent groundcover component in woodland gardens, bridging the gap between taller shrubs and ground-level mosses or ferns. Its preference for acidic soil means it pairs well with rhododendrons, azaleas, and woodland phlox, creating a cohesive, shaded tapestry.
Standout Features
Flower Qualities
- Showy
Noteworthy Characteristics
The specific epithet honors Benjamin Carroll Tharp (1885-1964), noted botanist and professor at the University of Texas. Tradescantia tharpii, commonly called Tharp spiderwort or shortstem spiderwort, is a compact, clump-forming perennial that is native to Missouri, Kansas, Oklahoma and Texas. Flowers are borne in terminal clusters atop short stiff stems, featuring three petals often in shades of rose to purple, accented by contrasting yellow stamens. When the stems of these spiderworts are cut, a characteristic viscous secretion is released that hardens into silky threads, giving rise to the common name.
Tolerances
- None listed
Potential Problems
Tradescantia tharpii is renowned for being exceptionally tough, facing no serious insect or disease issues when sited correctly. The primary threat often comes from early season garden pests. Young shoots are susceptible to damage from snails and caterpillars, who enjoy the tender new growth emerging in spring. Damage from slugs or snails can distort the emerging foliage, reducing the plant’s aesthetic appeal early on.
To manage these pests, apply preventative slug and snail baits or beer traps early in the season before significant chewing occurs. Another cultural challenge arises later in the summer when the foliage of the spiderwort often sprawls or declines unattractively following its primary bloom and seed set. The solution here is aesthetic maintenance: cut the stems back hard to the ground immediately after seed development to encourage clean, refreshed foliage growth for the remainder of the season.
Frequently Asked Questions
What hardiness zones is Tharp’s spiderwort suitable for?
Tradescantia tharpii is reliably hardy across USDA Zones 4 through 9.
How large does Tharp’s spiderwort grow?
This compact perennial typically reaches mature heights between 0.5 and 1 foot tall, with a similar spread of 0.5 to 1 foot wide.
What sun exposure does Tradescantia tharpii need?
This species performs best when situated in part shade to full shade locations in the garden.
When does Tradescantia tharpii bloom?
Tharp’s spiderwort generally blooms from May through July, with lovely rose to purple colored flowers.
Conclusion
Tradescantia tharpii offers reliable texture and subtle color perfectly suited for shaded woodland settings or woodland borders. Its medium maintenance requirement, coupled with its ability to naturalize, makes Tharp’s spiderwort an excellent choice for gardeners looking to establish low-maintenance native plantings. Check your local USDA zone compatibility before purchasing to ensure this resilient perennial thrives long-term in your landscape.
Companion Planting
Selecting appropriate partners is crucial for maximizing the impact of Tradescantia tharpii in a shade garden. Because Tharp’s spiderwort performs best in moist, acidic soil, companion plants that share these preferences will create a cohesive planting scheme. Consider pairing it with native ferns, such as Ostrich Fern (Matteuccia struthiopteris), which offer contrasting vertical texture against the strappy blades of the spiderwort.
Plants with different bloom times are also excellent companions; for instance, spring ephemeral bulbs like Mayapple (Podophyllum peltatum) will provide early interest, disappearing just as the Tradescantia tharpii comes into its peak flowering period. Later blooming shade perennials like Astilbe or Foamflower (Tiarella cordifolia) will take over when the spiderwort’s initial flush fades, ensuring continuous color.
Seasonal Care Calendar
Spring is the time to assess the plant after dormancy breaks; this is the best opportunity to cut back any old, dead foliage from the previous year and apply a light layer of compost if soil improvement is desired. Early spring is also when young shoots are most vulnerable, so monitor for snails and caterpillars, treating promptly as needed.
Mid-summer, once the main bloom is complete and seed heads have formed, is the ideal moment for rejuvenation pruning. Cutting Tradescantia tharpii stems close to the ground reinvigorates the plant, promoting clean new growth which may lead to beneficial rebloom into the fall months. Deadheading individual flower clusters as they fade also enhances the overall display during the May to July period.
Propagation Tips
Division is the easiest and most effective way to propagate Tradescantia tharpii and keep established clumps vigorous. Perform this task in early spring just as new growth begins to emerge or in early fall once temperatures cool slightly. Carefully dig up the entire clump and gently tease apart sections, ensuring each new division has a healthy set of roots and several viable shoots. Replant these divisions immediately into well-prepared, moist soil at the same depth they were previously growing.
While seed is an option, the germination process for many Tradescantia species can be slow and unpredictable, making division the preferred method for home gardeners seeking exact replicas of the parent plant. If you choose to save seeds, harvest the capsules when they begin to dry and mature after the initial bloom cycle, storing them in a cool, dry place until planting in the spring.
Common Mistakes
A frequent error when growing Tharp’s spiderwort is failing to prune back the foliage after the primary summer seed set. Allowing spent flowering stems to remain leads to a messy appearance where the foliage sprawls and yellows, masking the plant’s inherent neat structure. Remember that hard cutting back promotes renewal.
Another pitfall involves soil conditions; planting Tradescantia tharpii in heavy, poorly draining clay soil, especially in full sun, will almost certainly lead to root rot or scorching. This plant demands well-drained, acidic conditions; amending heavy soil with sharp sand and organic matter is crucial to mimic its native Texas and Missouri woodland habitats.
