In the days when we quickly had to order a few flowering shrubs to fill the instant colour aisles of our nurseries before a busy weekend, Solanum rantonnetii was always first on our shopping list. We just could not go wrong with ordering this plant, and it is still a bestseller because it is almost always in bloom, and to boast produces blooms in such a calming colour – purple, lilac or violet blue, depending on how you describe the colour.
If you glance at an individual bloom, it’s just a pretty flower (1,5 – 2,5 cm in diameter), attached to a relatively large shrub that generously produces hundreds of these flowers at a time. If you take the time to look long and hard at a single open flower, you appreciate its true beauty. It has a small, almost star-shaped glowing yellow heart with gold stamens, surrounded by light purple, soft, wavy, fused petals overlaid with an almost violet coloured daisy-like shape.
The Solanum Rantonnetii, or blue potato bush is a woody shrub that grows to about 2 x 2 m. It has a tumbling, drooping growth habit that makes it unsuitable for planting singly as a specimen plant; rather plant quite a few of them between other large shrubs in the background of a large bed, or in a row against a wire fence or palisade boundary. It tumbles over and grows through supports, so when planted along a boundary it gives pleasure to you and those passing by.
When does the Solanum Rantonnetii bloom?
Solanum rantonnetii flowers throughout the year, taking only short breaks. The flower production depends on the frequency of your pruning sessions. Every time it is tamed with a pruning tool, it rewards you with new foliage and more blooms.
Most suitable climate for Solanum Rantonnetii
It tolerates cold and light frost, but it can shed some of its leaves and become semi-deciduous during the colder months, despite being known as an evergreen. Temperatures that drop too low will kill it, so in very cold climates, rather plant it in a sheltered area. It flourishes in subtropical climates, growing luxuriantly and requiring lots of pruning. In places with dry summers and winter rainfall, it fares equally well.
What they need
Location: full sun or morning sun, in the company of other shrubs such as smaller bougainvillea types, plumbago and Cape honeysuckle (tecoma), which all prefer medium water.
Soil: well-drained sandy soil enriched with lots of organic material.
Water: too much watering or lots of rain results in lush foliage with few or no flowers. Allow the soil to dry out between watering sessions.
Fertilizing: feed during spring and late summer (preferably after a good pruning) using potassium-rich fertilizer.
Watch out for this
- All the ornamental plants in the potato family are poisonous. (The blue potato bush and the ordinary potato are both classified in the same plant family, Solanaceae.)
- This plant needs to be pruned back heavily on a regular basis to promote bushy growth and lots of flowers.
Other uses in the garden
Clever commercial growers quickly recognized the potential of S. rantonnetii for creating standards or lollipops, because it reacts so well and so quickly to drastic pruning. In the controlled shape of a standard, you can use these plants in flowerbeds, and in large garden pots, where they will be far more prominent than in their usual background position. When they are grown in this fashion, the growth points need to be pinched off very regularly to maintain the formal shape. This also ensures that they remain dense and lush with plenty of flowers.
In a nutshell
- Too much water means fewer flowers.
- Too little sunlight causes sparse growth.
- Plant in a sheltered position in very cold regions.
- Solanum rantonnetii ‘White’ has snow-white flowers with yellow throats.
- Solanum rantonnetii ‘Variegatum’ has a pretty variegated leaf type with pale green and cream foliage and lightly scented blue to violet flowers with yellow centres. The variegated leaf types do not grow as fast as the ordinary ones and in warm regions fare better in light shade where the foliage will not get sunburned.
- Solanum rantonnetii ‘Montreux’ is a 2 x 2 m evergreen with deep violet-blue flowers with yellow centres, a good container plant as well as a strong summer colour plant with other shrubs in a garden bed. It is fairly low maintenance but must be regularly pruned. Plant in full sun to light shade and avoid heavy frost areas.