How to Grow and Care for Nierembergia (Cupflower)

If you are looking for a long-blooming annual plant for your garden or a container, consider the various species of Nierembergia, also known as cupflower. Sizes vary depending on species, but all plants have finely textured, stiff leaves that grow from multiple stems. From early summer through fall, the plants are covered in blue, purple, or white star-shaped saucer-like flowers with yellow centers and are known to hold their color in even the brightest sunlight.

Nierembergia is most often planted in the spring from potted nursery plants or started from seeds indoors in late winter. Seedlings grow slowly at first, but then grow more quickly once transplanted in the garden. When grown from seed, it takes about four months to produce flowering plants.

Nierembergia is not included on any lists of plants that are toxic to humans or pets, even though it is a member of the Solanaceae (nightshade) family, which includes many toxic species. However, there are some reports of neurotoxicity in grazing animals, such as sheep and cattle, when they feed on it.

Common Name	Cupflower
Botanical Name	Nierembergia spp.
Family	Solanaceae
Plant Type	Tender perennial usually grown as an annual
Mature Size	6–30 in. tall, 6–18 in. wide (varies by species)
Sun Exposure	Full to partial sun
Soil Type	Rich, moist but well-drained
Soil pH	Acidic to alkaline
Bloom Time	Late spring to first frost
Flower Color	Blue, purple, white
Hardiness Zones	7-10 (USDA)
Native Area	South America
Toxicity	Possibly toxic to grazing animals

Nierembergia Care

While most species are technically tender perennials, hardy in USDA cold hardiness zones 7 to 10, Nierembergia is grown as an annual in most areas. It grows easily in moist, rich, well-drained soil in full sun or partial shade. Space plants 6 to 12 inches apart. Other than watering and fertilizing, the plants are low-maintenance, but they do benefit from deadheading spent flowers and gently trimming new growth to encourage repeated bloom. Despite the fact that they are perennials in warm climates, these plants do not care for extremely warm soil, so a thick layer of mulch is recommended to keep the soil cool.

Light

Nierembergia can be grown in full sun but it prefers light shade during the hot afternoon hours. Shade is especially important where summer temperatures are very hot.

Soil

The soil should be rich in organic matter and have good drainage. Mulching helps to retain soil moisture and keeps the soil cool. Using well-aged composted manure as mulch has the double benefit of keeping the soil cool and adding nutrients.

Water

Nierembergia needs consistently moist soil so water regularly as needed (about one inch per week). Overwatering, on the other hand, can lead to root rot and other fungal diseases. Mature plants have good tolerance for short periods of drought, and a week without water is usually not problematic.

Temperature and Humidity

Although Nierembergia is hardy in zones 7 to 10, it does best where summers are relatively cool, and flowering will decline noticeably in hot-summer climates. Thus, it is more popular as an annual in northern climates than as a perennial in southern regions. It does equally well in arid and humid environments provided soil moisture is adequate.

Fertilizer

Fertilize about once a month with a complete fertilizer. These are heavy flowering plants that need plenty of nutrients. A heavy layer of good organic mulch, such as well-decomposed manure, can reduce the need for additional fertilizers.

Types of Nierembergia

When you shop for Nierembergia plants or seeds, be prepared for some confusing botanical nomenclature. Several Nierembergia species and their names are often used interchangeably. The two most popular species are Nierembergia scoparia (12 to 30 inches tall) and Nierembergia hippomanica (6 to 12 inches tall). Nierembergia scoparia is the taller, more shrub-like species, and Nierembergia hippomanica is the dwarf, more compact species. However, the names are not always properly used, so make sure to also pay attention to plant size specifications on the plant label.

Some of the more popular cultivars include:

• Nierembergia hippomanica ‘Mont Blanc’ is a compact cultivar with small white flowers.
• Nierembergia hippomanica ‘White Robe’, also a compact cultivar with white flowers, blooms earlier than other varieties.
• Nierembergia scoparia ‘Purple Robe’ has blue-violet flowers.
• Nierembergia gracilis ‘Starry Eyes’, is a cultivar of a Nierembergia species that is native to the Argentinian desert and is thus very drought-tolerant. Its white flowers have pale lavender highlights.
• Nierembergia ‘Summer Splash’ is a hybrid perennial for warm climates (zone 8 to 11 depending on the variety). These compact or trailing plants have white or light blue flowers.

Pruning

Pinching back young plants and regular deadheading of spent flowers will encourage additional blooming. When the plants fade in fall, simply pull them from the ground and discard them—unless you live in a zone where they can be grown as perennials. Plants that decline in the summer heat will respond well to a severe cutback, producing vigorous new growth when temperatures cool down.

Propagating Nierembergia

Nierembergia is most often propagated by stem cuttings. This can be done at any time, but late fall propagation is popular as a means for continuing plants over the winter. Here's how to do it:

1. Using sharp pruners, cut a four- to six-inch cutting from an actively growing branch.
2. Remove the leaves from the bottom half of the cutting and dip the cut end in rooting hormone.
3. Plant the cutting in a small container filled with seed starter mix. Moisten thoroughly, then place the container in a loosely secure plastic bag.
4. Keep the potting medium slightly moist and check weekly to see if it has rooted.
5. When roots have formed (you'll feel resistance when gently tugging on the stem) remove the plastic and continue growing the cutting in a bright location that is not too warm (60 to 65 degrees Fahrenheit is ideal).
6. Plant the propagated plant in the garden in the spring, after hardening off, and all danger of frost has passed.

Nierembergia can also be propagated by dividing the root clumps in spring, as new growth is just beginning, or by seeds collected from the dried flower heads (see below).

How to Grow Nierembergia From Seed

To get a head start on summer, eight to ten weeks before your average last frost date, start seeds in flats in sterile potting soil. The seeds need light to germinate so they should be barely covered with soil. Kept the soil evenly moist at 70 degrees Fahrenheit. Germination should occur within two to three weeks. Once the seedlings emerge, water less frequently and only when the soil dries out.

The seedlings will grow slowly but will grow quicly after transplanting. After hardening off the seedlings, transplant them outdoors, 6 to 12 inches apart, in rich, well-drained soil. Once the plants start growing, pinch them to encourage bushy growth.

Potting and Repotting Nierembergia

Due to its compact growth habit, Nierembergia is a good choice for containers, including hanging baskets and window boxes. Ordinary commercial potting soil is sufficient; make sure the containers drain well. Keep in mind though that container plants and hanging baskets need more frequent watering, and protect containers from the direct, hot afternoon sun to prevent root damage.

Potted Nierembergia does not winter indoors very well. It's usually best to discard plants at the end of the growing season and start with new plants in the spring.

Overwintering

At the end of the growing season, Nierembergia plants are typically pulled from the garden and discarded. If you live in a region with a long growing season, you can leave some plants in place and allow them to self-seed.

If live in a warm weather zone where Nierembergia can be grown as a perennial, then clip off the plants at ground level for the winter, rather than pulling them. They will sprout new growth from the root crown in the spring.

Common Pests and Plant Diseases

This plant does not have major serious insect or disease problems but watch out for aphids and whiteflies, along with slugs, and snails. Insect pests can be treated with a horticultural oil ; slugs and snails are best picked off by hand or baited.

Nierembergia is also susceptible to tobacco mosaic virus, a disease that affects many plants in the nightshade family. The virus is identified by yellow mottling on the leaves, and there is no cure. Affected plants should be removed and destroyed to prevent the spread of the disease.

How to Get Nierembergia to Bloom

These long-blooming plants need regular fertilizing in order to produce their profuse blossoms, so feed them monthly during the growing season. Very hot weather might cause the plants to decline temporarily; sharply pinching them back will prompt vigorous reblooming when temperatures are cooler in early fall.

Common Problems With Nierembergia

Plants Decline in Summer

Despite the fact that this plant is perennial in warm-weather zones, it does not like extremely hot summer weather and might decline radically in the heat of a southern summer. However, the plants will usually recover nicely if you cut them back severely and wait for cooler weather to return.

Plants Turn Soft and Mushy

Nierembergia thrives on consistent moisture, but once the plants are established, it's better to err on the side of too little water rather than too much. They have good tolerance for short periods of drought, but too much water can cause root and stem rot, causing the plants to collapse. There is no need to irrigate plants when rainfall is providing adequate moisture.