Native to Argentina, Bolivia, Brazil, and Paraguay, the blue potato bush is cultivated all over the world for its unforgettable, lightly fragrant, and beautiful deep purple-blue flowers with yellow centers. The Lycianthes rantonnetii has even been awarded the Royal Horticultural Society's prestigious Award of Garden Merit. The use of nightshade in one of its common names is not surprising because this plant was mistakenly thought to be one of the nightshade species, even though it is not.
The large leaves of the blue potato bush are oval to elliptical, but the flowers of this species make the plant memorable. In cooler zones, the plant is described as deciduous with blossoms produced from March through October, while in the warmest zones it's considered an evergreen that may bloom year-round. Flowering is most prolific during the summer months. Its poisonous seed-bearing fruit is produced in the form of inedible, small, and bright orange-red oval berries.
|Botanical Name||Lycianthes rantonnetii, Solanum rantonnetii|
|Common Name||Lycianthes, Paraguay nightshade, and royal robe|
|Mature Size||6-10 ft. height, 6-10 ft. width|
|Sun Exposure||Full sun|
|Soil Type||Well-drained, loamy|
|Soil pH||Acidic, alkaline, or neutral (6.0 to 9.0)|
|Bloom Time||March-October or year-round in warmer areas|
|Hardiness Zones||8-11 (USDA)|
|Native Area||South America|
|Toxicity||Toxic to humans|
Blue Potato Bush Care
Well-suited to many garden types, the blue potato bush makes an excellent backdrop for small shrubs and perennials. It can be used as a focal piece in a garden or mixed in with other plants as a border. This species can also be grown in containers and makes a striking display on a patio. This non-invasive, but fast-growing species is suitable for planting in USDA hardiness zones 8 through 11. In colder zones, it may drop its leaves in the winter, while in the warmer zones it remains evergreen.
Another use for the blue potato bush is as a hedge or screening plant. Take care with placement, as all parts of this plant are poisonous. The berries, in particular, might be appealing to young children.
The blue potato bush is a fast-growing evergreen that will grow to as much as 10 feet in height and width. Although this species requires little maintenance, it should be pruned regularly to retain a pleasing shape.
Blue potato bush prefers full sun, if possible, but will tolerate partial shade in warmer areas.
Loamy soil should be well-drained but not allowed to completely dry out before the next watering.
Regular watering is important, particularly during the first growing season. Water more frequently during times of high heat.
Temperature and Humidity
This species fares well in sunny, frost-free, and coastal regions but should be protected from strong winds.
Apply a slow-release fertilizer in the spring just before new growth begins. If planted in a container, fertilize once a month with a liquid 10-10-10 fertilizer. Mulch roots with compost in the spring and again in the fall.
Blue Potato Bush Varieties
Several cultivars have been produced with different colored foliage and blossoms. The cultivar Lycianthes rantonnetii 'White' has beautiful snow-white flowers, while Lycianthes rantonnetii ‘Variegata’ has cream and grey-green leaves with blue flowers. All varieties are sweetly scented and attract butterflies.
This plant can become unruly in its appearance if not pruned. The smooth gray-brown branches grow in an arching fashion, sprawling to well over 6 feet if not pruned. On a bright note, if the shrub is not pruned, this species will also produce berries which will attract a variety of birds.
Primary pruning should take place in the winter months after blossoming has ceased. Light pruning at this time after each batch of flowers will result in a compact shape and encourage greater blossoming. No more than a third of each stem should be cut back.
They can be pruned to almost any shape and are often trimmed to a tree shape with the lower foliage clipped. If managed well, this species can be pruned to a round shape with minimal loss of flowers.
Propagating Blue Potato Bush
Propagating blue potato bush from cuttings may be easier and safer than foraging the seeds from the poisonous berries. Take your cuttings from summer to early fall, and propagate with these steps:
- Take a cutting of about 4 to 6 inches, cutting the stem right below a leaf node.
- Remove leaves from the stem, leaving at least two at the top of the cutting.
- Dip the bottom of the stem in rooting hormone.
- Insert stem into well-draining soil.
- Put a plastic bag or plastic bottle (with the bottom cut out) over each cutting.
- Place the container in a warm area with bright sun.
- Water well.
- Cuttings will root in about a month.
- Gently tug on stems to see if the roots have formed; if they are easily moved, roots have not yet formed.
- When roots have formed, remove plastic and transplant outdoors or replant in a large container.
Potting and Repotting Blue Potato Bush
Blue potato bush can be grown in outdoor containers. Choose a large pot to contain the plant's height and width. Line the bottom of the pot with gravel. Keep soil moist and well-drained, and keep in a sunny spot outdoors.
Plants can be grown into a small potted tree by removing the lower branches and pruning the remaining foliage to the desired shape. By doing this, the bush can be trained over time in the container to become shaped as a topiary lollipop (clear stem) or espaliered (clear stem with foliage growing flat against a wall or trellis).
If blue potato bushes are potted, bring them indoors when the threat of frost arrives. Continually or abruptly moving a potted blue potato bush from outdoors to indoors, however, can stress the plant and result in yellowing and dropping leaves.
Common Pests & Diseases
The blue potato bush is susceptible to pests such as aphids, caterpillars, and thrips. Aphids can be removed by directing a strong spray of water early in the day to allow leaves to dry before nighttime. Thrips can be managed by the use of horticultural oils, neem oil, or spinosad.