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 more quickly once transplanted in the garden. When planted from seeds, 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 Nierembergia.
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 1 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 a problem
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 lessen the need for chemical fertilizers.
Types of Nierembergia
When you shop for Nierembergia plants or seeds, be prepared for some confusing botanical nomenclature. There are 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 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 dead-heading 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 moderate.
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: 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. 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 take off 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 plant for containers, including hanging baskets and window boxes. Ordinary commercial potting soil is sufficient; make sure the containers are well-draining. 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 afresh in the spring.
Overwintering
At the end of the growing season, Nierembergia plants are normally just 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
The 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 or chemical pesticide; 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 may cause the plants to decline temporarily; sharply pinching them back will prompt vigorous reblooming when temps drop again 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 may 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 drought, but too much water can cause root and stem rot, causing the plants to collapse. There is no need to irrigate plants on weeks when rainfall is providing adequate moisture. This is a good plant for gardens where deer are a nuisance, as these browsing animals seem to be put off by Nierembergia.
Propagation by seed is better done from commercial purchased seed or collected seeds that are started indoors eight to ten weeks before outdoor planting time. In this fashion, you’ll be assured of summer blooms.
