<em>Solanum</em>: planting, pruning, cultivation

Description and botany

The Solanum is a sarmentous climbing plant belonging to large botanical family Solanaceae, just like potato (Solanum tuberosum), tomato and the toxic belladonna and Datura.

It is native to warm, humid regions, notably South America, more precisely Brazil and Chile. Genus Solanum comprises about 1,400 herbaceous, shrubby and arborescent species including Solanum jasminoides, recently renamed Solanum laxum but commonly called “false-jasmine nightshade”, Solanum crispum, another luxuriant liana, and Solanum rantonetii, often called “gentian tree” or “tree gentian” because of intensity of its blue-violet flowers: very floriferous, it is widely cultivated.

They have produced interesting cultivars with white or ultramarine blue flowers.

Not to forget Solanum pseudocapsicum, better known as “Jerusalem cherry” or “Jerusalem cherry tree” with its round, fleshy fruits resembling small tomatoes in orange, yellow or red.

All are tender and only planted outdoors in areas free from frost. They are classic features of Mediterranean gardens. In more continental regions, they are easily grown in a large pot and moved indoors for winter.

With very rapid growth, this sarmentous climber, once established, develops long flexible, almost voluble shoots that clamber over any support. Size varies according to Solanum species.

Solanum jasminoides and Solanum crispum can reach adult size, on average 5 to 6 m high and nearly as wide, within one or two seasons. If left unrestrained, they can spread as groundcover.

Solanum rantonetii forms a bushy plant with often trailing shoots and shows less vigorous development: it will not exceed 2 m in height and will present a frequently very ramified silhouette at maturity.

Some Solanums: S. jasminoides ‘Album’, S. crispum, S. pseudocapsicum and S. rantonetii

Solanum pseudocapsicum forms a small, rounded, very ramified shrub not exceeding 45 cm in height. With its miniature-tree appearance, it is so often grown indoors that it is nicknamed “apartment Solanum”.

Shoots, more or less flexible and trailing, carry an elegant luxuriant foliage reminiscent of jasmine. Foliage is evergreen to semi-evergreen in mild climates but can be deciduous if exposed to frost. Leaves, arranged alternately along stems, are oblong to lanceolate, or strongly pinnate, sometimes divided into 3 or 5 lobes or bearing lobed leaflets, often with undulate margins. Measuring from 2 to 25 cm according to species, they are glossy or downy.

Colours range from bright green to dark green, sometimes reddening with cold. Some cultivars bear sumptuous variegated foliage with cream.

This luxuriant vegetation forms an elegant setting for flowering. Solanum is prized for its flowers and decorative fruits.

Plant becomes covered with a multitude of small flowers that renew continuously from May until first frosts. Flowering can sometimes last up to eight months in regions where frost does not occur. Five-petalled flowers are bell-shaped, trumpet-flared or more often small stars, typical of Solanaceae (hence nickname “Star of Bethlehem”).

Solanum jasminoides ‘Album’

They measure from 1 to 6 cm in diameter and open in numerous small clusters, sometimes umbel-like or paniculate, 2 to 15 cm wide, in axil of leaves or at ends of shoots.

Often characterised by a violet-blue recalling gentian, some cultivars offer very bright light blue or pure white flowers highlighted by a cluster of prominent yellow-orange stamens.

Slightly scented, flowers exude a discreet jasmine-like perfume. After flowering, they turn into fruits, small toxic berries if ingested, round or ovoid, violet, red, vermilion, orange or yellow, 1 to 2 cm diameter. This decorative fruiting is nevertheless rare in our climates.

Fortunately, Solanum pseudocapsicum, most often grown as a seasonal indoor plant, allows enjoyment of decorative potential of these fruits that last throughout autumn and much of winter when this shrub is kept warm or grown outdoors in mild climate. Dotting whole plant, like cherry tomatoes or tiny oranges, initially green, they turn yellow, orange then bright red on ripening. They inspired nicknames for this Solanum species such as Jerusalem cherry and shoemaker’s orange.

Like jasmine, Solanum is quite tender, rarely enduring temperatures below -5 °C/-8 °C. It is easy to grow outdoors in very mild-winter regions. It is a classic of Mediterranean gardens but can adapt as far as Paris region in very sheltered situations. Elsewhere, in cold climates it should be reserved exclusively for container culture and wintered frost-free, like conservatory plants.

It needs heat and sun as well as a fertile, cool but very free-draining soil.

Solanum rantonetii with sumptuous intense blue-violet flowers

This sarmentous liana is easily trained against a wall, a trellis, a pergola. Untrained and left free, it can also form a magnificent, somewhat tangled and wild groundcover.

Its light flowering brings much charm and elegance to garden or terrace.

Main species and varieties

More than 1,400 species of Solanum, among them classic Solanum jasminoides with star-shaped white, blue or violet flowers and Solanum crispum, the hardiest of the Solanums, which are two vigorous but tender lianas. Solanum rantonnetii, “gentian tree”, is a more shrub-like species with an astonishing gentian-blue of flowers!

All have produced sumptuous cultivars that have enriched palette of blues, ranging from pastel blue to most intense ultramarine blue.

Collect in garden or year-round in conservatory!

Most popular

Solanum jasminoides Blue

A slender, evergreen liana in mild climate. Fast growth, very floriferous, to train against a wall or to let climb on a trellis or fence.

• Flowering time July to November
• Height at maturity 5 m

See the product sheet

Solanum crispum Glasnevin

It continuously produces an abundance of mauve flowers. The hardiest of the Solanums! It climbs trellis, arch, pergola, stair banister... It can also be grown in a container on a terrace in colder regions.

• Flowering time July to November
• Height at maturity 5 m

See the product sheet

Solanum rantonetti

It is called 'Gentian tree' because of the intense blue of its flowers! Hardy only down to -5°C, it is very well suited to Mediterranean climate. Elsewhere, it should be confined to pot culture and wintered frost-free.

• Flowering time July to November
• Height at maturity 2 m

See the product sheet

Our favourites

Solanum jasminoides Blue

We love this great classic of Mediterranean gardens, easy to grow in mild climate!

• Flowering time July to November
• Height at maturity 5 m

See the product sheet

Solanum jasminoides Album

A superb form with white flowers! This false jasmine is as decorative as the blue-flowered type. Hardier than it looks!

• Flowering time July to November
• Height at maturity 5 m

See the product sheet

Planting

Where to plant Solanum?

From its tropical and subtropical origins, Solanum has retained a marked sensitivity to cold. Not very hardy, it does not tolerate severe frosts. It is easy to grow in the open ground in Mediterranean or coastal areas, elsewhere its hardiness will be severely tested.

Foliage is destroyed by cold from 0°C–2°C, while its stump survives only down to about −5°C. Some are hardier than they appear, sometimes resisting down to −8 to −10°C in a well‑sheltered position, under a thick protective mulch, the stump resuming growth in spring without difficulty.

In regions with harsh winters, north of the Loire, grow Solanum in a large container, well sheltered on a terrace and overwinter indoors, protected from frost.

It needs warmth and sun: give it a very sunny position, sheltered from draughts. In hot climates it prefers semi‑shade rather than scorching sun that burns its flowers.

Once well established it is drought‑resistant in summer and can cope with ordinary, even slightly calcareous soil, provided it is always perfectly drained. It prefers fertile, deep soils in which it will truly flourish.

Solanum has a thousand uses in a mild‑climate garden: flowering an arbour, winding around a tree, dressing a well‑exposed wall, a trellis or a wire fence… What a joy when it provides welcome shade after covering a pergola! Its foliage remains semi‑evergreen in mild climates: a useful asset when masking an unsightly wall or façade. Untrained, it forms an elegant groundcover.

This woody liana needs an airy spot because its growth is rapid from the first year after planting.

Some solanums, such as Solanum rantonnetii, can even be trained as standards or grown as bonsai.

The Solanum will also form a pretty, floriferous shrub in a large pot, well sheltered on a balcony or terrace, to be brought indoors to protect from frost in cold regions. For indoor‑grown Christmas cherries, place near a window but avoid scorching sun.

When to plant Solanum?

Planting Solanum is done in spring, from March to May after last frosts, because this plant is frost‑tender. Meanwhile, you can pre‑cultivate it in a pot in a warm, bright room to hasten growth. Planting in September–October is possible in mild climates.

How to plant Solanum?

Given the rapid and vigorous development of Solanum, 1 plant per m² is sufficient as it can spread 3–6 m in just two or three seasons. Dig at 20 cm from wall or support used.

• Soak the rootball in a bucket of water before planting
• Dig a hole two to three times wider than the rootball
• Spread a layer of gravel or clay pebbles to improve drainage
• Mix a little well‑rotted compost into the excavated soil
• Position the plant with base of stems level with the soil
• Backfill the hole
• Firm down lightly
• Water generously
• Mulch the base to keep cool in summer
• Train branches onto the support

How to plant Solanum in a pot?

Substrate must be very free‑draining to avoid stagnant moisture at the roots of Solanum.

• In a large terracotta pot, place a good drainage layer (gravel or clay pebbles) to one quarter of the pot height
• Plant Solanum in compost for Mediterranean plants or for geraniums, or in a mix of turf, sand, leaf mould and garden soil
• Train stems onto the support
• Water
• Overwinter the pot in a frost‑free but light place, such as a conservatory or cool greenhouse

→ Learn more about growing Solanum in a pot in our advice sheet: Solanum en pot.

Maintenance, pruning and care

Le Solanum requires little care once established. Sun and regular watering are the secrets to ensure good development.

In ground

Water regularly and thoroughly during first year after planting to aid establishment. Afterwards it will tolerate drought well and will only need occasional watering in summer to support flowering.

The Solanum is quite greedy and needs fertile soil to improve flowering. It benefits from regular feeding during growth, especially in poor soil. A top-dressing of compost by forking in in spring and summer will encourage and prolong flowering.

Train new shoots as they develop. Regularly remove faded flowers to encourage renewal of flowering.

In mild regions, if severe cold is forecast, protect aerial parts with a winter fleece and mulch the stump from October with dead leaves. More information in our advice sheet “How to protect Mediterranean plants from cold”.

In areas with harsh winters, bring potted solanums indoors before first frosts, keeping them frost-free in a very bright room.

In a pot

The Solanum grown in a pot must be watered more frequently. Water regularly, avoiding letting the rootball dry out when it is hot. During growth water once or twice a week and apply a liquid fertiliser twice a month. Reduce watering in winter to once every two weeks and stop all feeding.

Frequently mist foliage with limescale-free water if you want to keep your potted Solanum indoors year-round, as leaves and flowers wilt quickly when atmosphere is too dry.

Top-dress each year in spring with compost and repot every 3 years in spring, annually for Solanum pseudocapsicum.

Bring pots indoors as soon as temperatures fall below 2–3°C and overwinter them out of frost in a greenhouse or a minimally heated conservatory where temperature will not drop below 10°C. You can put them back outside in spring when temperatures have warmed and frosts are definitely over.

→ Learn more in our advice sheet How to overwinter a Solanum?

At the start, help stems climb their support and train them as they develop.

When and how to prune a Solanum?

No pruning is strictly necessary, but it can be useful to contain growth!

For Solanum jasminoides and crispum, pruning simply involves controlling spread, removing weak or damaged branches and balancing the branches to restore a pleasing rounded habit.

Solanum tends to become invasive but tolerates pruning well, even severe pruning, and does not mind being cut back annually.

• Prune each year in spring, early March.
• Cut stems back to three to four buds (about 30 cm from soil) and remove old branches and broken stems.
• You can also refresh the liana throughout the season without problem to control congestion or encourage branching.

Pruning Jerusalem cherry is not necessary every year given its limited growth. Pinch young stems in spring to encourage branching and cut stems back by half every three years if you have managed to keep this species that long, as very dry indoor air often proves fatal after a year.

Training a Solanum as a standard

It is easy to train Solanum rantonnetii or « Arbre aux gentianes » as a small standard bush by pruning lower branches.

→ Learn more in our tutorial: How to prune a climbing or standard Solanum?

How to train Solanum?

Stems of Solanum do not have tendrils, which is why it is necessary to train them by tying with ties as soon as they are planted in ground or in a pot. Supports are many: Solanum can take support against a wall, cascade over top of a low stone wall, twine around a tree, climb a wire fence or a trellis.

On a smooth wall: fit hooks and stretch nylon lines horizontally every 50 cm to guide stems.

Potential diseases and pests

The Solanum has no enemies; only plants grown indoors may be more vulnerable to red spider mite infestations, common when the plant lacks water and when the environment is too dry and confined. To eliminate them, spray with a stinging nettle infusion.

Aphids are sometimes visible on leaves. Spray with soapy water.

Propagation

Le solanum multiplies easily by cuttings of herbaceous stems between April and June. Layering is also possible, though more tedious.

How to propagate solanum?

Solanum cuttings will flower from following summer.

• With pruning shear, take 5 to 8 cm cuttings from supple, green, non-flowering shoots
• Remove lower leaves
• Push cuttings into buckets filled with potting compost, turf and sand
• Firm down and water
• Regularly moisten substrate with a spray bottle
• Place pot in partial shade under cover, frost-free in winter at a temperature between 10 and 15 °C in greenhouse or conservatory
• Plant in ground or repot each cutting individually the following spring

By layering

Layering solanum at end of autumn produces rooted layers about one year later.

• Dig a long trench 15 cm deep and 1 to 2 m long depending on length of chosen shoot
• Bend this long low stem down towards soil
• Remove lower leaves
• Make a notch in the bark of about 3 to 5 cm on sections to be buried, at a node
• Bury one or several sections 15 cm deep to encourage rooting
• Secure layers in soil with metal pegs driven into soil
• Cover with potting compost, firm down and water
• Thereafter, water when soil is dry
• One year later, the following autumn, separate layers from parent plant; they will be sufficiently rooted: cut stems where they enter soil
• Replant layers in ground at permanent position or in pots

Associate

Slender and of rare elegance, Solanum thrives in gardens of varied styles, giving them charm and poetry. It is a staple of blue or white romantic gardens. Above all, it is a classic in Mediterranean and exotic gardens, where it brings a refreshing presence in summer.

While Solanum does well alone on a trellis or a fence, it is found in fresh, romantic combinations with climbing roses and other beautiful climbing plants such as clematis, honeysuckle, jasmine, passionflower, a trumpet creeper (Campsis radicans) or Podranea ricasoliana.

An exotic pairing idea: Solanum jasminoides ‘Album’ (or ‘Blue’) on a structure with a few Dahlia ‘Victoria Ann’ in front, accompanied by Colocasia ‘Madeira’

In a Mediterranean garden, for a more exotic touch, pair it with a Mediterranean climbing plant such as bougainvillea or Plumbago capensis (Cape leadwort).

In our mildest regions, train it against a wall in open ground at foot of Mexican orange, abutilon or tree mallow.

In a pot kept warm over winter, it pairs perfectly with Convolvulus mauritanicus or Ampelaster carolinianus, a climbing aster that flowers in late autumn.

→ Discover other ideas for pairing Solanum