Cupflower (Nierembergia scoparia 'Purple Robe')

Overview

The Nierembergia scoparia ‘Purple Robe’, commonly known as Cupflower, is a jewel for the late spring and summer garden. Valued for its masses of small, cup-shaped, violet-blue flowers, this cultivar provides excellent ground-level texture and color until the first hard frost. It forms a dense, spreading mound ideal for softening borders or filling containers.

As a tender perennial, Nierembergia scoparia ‘Purple Robe’ provides reliable color, often treated as an annual in cooler climates. It thrives when provided with consistent moisture and well-drained, rich soil. Gardeners seeking continuous, low-growing bloom that prefers cooler summer conditions will find the Cupflower indispensable.

This compact variety, reaching only about 6 inches tall, requires moderate care but offers significant visual returns, especially in mixed plantings where its delicate foliage and flowers can stand out. Its ability to perform well through periods that slow down other bloomers makes the Nierembergia scoparia ‘Purple Robe’ a highly practical choice.

Fast Facts

• Plant Family: Solanaceae
• Plant Type: Herbaceous perennial
• Hardiness Zones: USDA Zones 7-10
• Size at Maturity:
  • Height: 0.25-0.75 ft
  • Spread: 0.5-1 ft
• Bloom Time: May to frost
• Bloom Description: Violet-blue
• Sun Exposure: Full sun to part shade
• Water Needs: Medium
• Maintenance Level: Medium

How to Grow

Sow seeds of the Cupflower indoors 6-8 weeks before your area’s last expected frost date, or sow seeds directly into the garden 1-2 weeks before this date. Transplant seedlings or purchased plants out just before the threat of frost to ensure success. Nierembergia scoparia ‘Purple Robe’ prefers moist, organically rich, well-drained soils.

Maintain consistently moist soil conditions throughout the growing season; this plant will not tolerate drying out. While it enjoys full sun, those in regions experiencing intense summer heat will see better performance if the plant receives some part afternoon shade, especially during the hottest part of the day. Applying a summer mulch is beneficial as it helps retain vital moisture and keeps the soil temperature cooler around the roots.

Pinch back young plants early in their development to encourage a bushier, more floriferous habit. Deadheading spent blooms helps stimulate the production of new flowers. A crucial mid-season tip: if flowering slows significantly due to summer heat, cut the plants back by about one-third. This pruning will encourage a fresh flush of blooms as temperatures moderate.

If you successfully site your Cupflower in a sheltered spot with a southern exposure, it may survive a mild winter (Zones 7-10). For guaranteed overwintering, take cuttings in late summer and bring them indoors.

Landscape Uses

The compact mounds of Nierembergia scoparia ‘Purple Robe’ make it exceptionally versatile in landscape design. It excels when used for crisp edging along pathways or defining the front of a mixed border, providing a low, colorful ribbon of violet-blue. Consider using this Cupflower in containers, hanging baskets, or window boxes where its trailing habit can cascade gently over the edges.

Because of its medium water needs and preference for cool conditions, pair it with other mid-season bloomers that share similar cultural requirements, such as calibrachoa or low-growing impatiens in partial shade settings. In rock gardens, the low-growing, spreading habit of the Nierembergia scoparia ‘Purple Robe’ works beautifully nestled between stones.

Utilize this variety to create visual flow within tiered plantings. Place taller perennials behind it, allowing the Cupflower to fill the gap between hardscape elements and taller background specimens, ensuring continuous color near eye level.

Standout Features

Flower Qualities

• Showy

Noteworthy Characteristics

Nierembergia scoparia, commonly known as cupflower or tall cupflower, is typically described as a shrubby tender perennial that forms a dense spreading mound. The ‘Purple Robe’ cultivar is specifically noted as being compact, reaching only about 6 inches tall and spreading to 12 inches wide, all covered in striking violet-blue flowers. While the genus offers pale blue cup-shaped flowers to 1 inch wide, this cultivar offers dense, low cover perfect for edging beds and borders throughout the season.

Tolerances

Potential Problems

Nierembergia scoparia ‘Purple Robe’ generally exhibits few serious insect or disease issues, which contributes to its ease of use. Gardeners should, however, remain vigilant for slugs and snails, which can chew on the foliage and tender stems, especially during moist periods.

The primary disease concern noted is susceptibility to tobacco mosaic virus, though this is relatively uncommon if introducing certified clean stock. To manage slugs and snails, employ cultural controls like removing debris or using appropriate baits or handpicking when populations are detected. Proper spacing and soil drainage can also help mitigate common fungal issues associated with overly damp conditions.

Frequently Asked Questions

What hardiness zones is Cupflower suitable for?

Nierembergia scoparia ‘Purple Robe’ is winter hardy as a perennial in USDA Zones 7 through 10, though it is often grown as an annual elsewhere or in cooler parts of Zone 7.

How large does Nierembergia scoparia ‘Purple Robe’ grow?

This variety is notably compact, typically growing between 0.25 and 0.75 feet tall (3 to 9 inches) and spreading between 0.5 and 1 foot wide.

What sun exposure does Cupflower need?

This plant prefers full sun but performs best and maintains better bloom during hot summers when sited with part shade, particularly afternoon shade.

When does Nierembergia scoparia ‘Purple Robe’ bloom?

The Cupflower produces its lovely violet-blue blooms consistently from May until the first frost touches the garden.

Conclusion

The Nierembergia scoparia ‘Purple Robe’ is a resilient and beautiful choice, offering continuous mounds of violet-blue flowers that enrich borders and containers. Its manageable size and pleasing cultural requirements make the Cupflower a dependable element in beds requiring consistent mid-season performance. Ensure your soil stays consistently moist and consider afternoon shade in hot climates, then plan your first planting around your last spring frost date.

Companion Planting

When selecting neighbors for Nierembergia scoparia ‘Purple Robe’, focus on plants that share its medium water requirements and preference for cool summer performance. Annual companions like sweet alyssum or dusty miller provide a soft, contrasting texture near the fine foliage of the Cupflower. For perennial borders in Zones 7-10, consider pairing it with Heuchera cultivars, which offer contrasting foliage colors without demanding excessive heat tolerance.

In foundation plantings or rock gardens, group the Cupflower with other similar low-growing spreads like creeping thyme or certain sedums. These companions help keep the soil surface cool and moist, which benefits the Nierembergia scoparia ‘Purple Robe’ and prevents competition for moisture near the soil line.

Propagation Tips

While often treated as an annual, increasing your stock of Nierembergia scoparia ‘Purple Robe’ is straightforward via late-summer cuttings. Take four-inch tip or stem cuttings just before fall weather turns cold. Ensure the cuttings are free from flower buds and place them in a moist rooting medium, such as a mix of peat and perlite, under high humidity conditions.

To successfully overwinter the cuttings, place them in a sheltered, minimally heated environment, like a cold frame or a protected porch, especially in northern zones. If you successfully overwinter any parent plants in a mild Zone 7 location, ensure they are heavily mulched and protected from winter wetness. Propagating the Cupflower ensures you have healthy, established young plants ready to set out again next spring.