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

Description and botany

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

It originates from warm, humid regions, notably South America, specifically Brazil and Chile. The genus Solanum includes about 1,400 herbaceous, shrubby and arborescent species, among them Solanum jasminoides, recently renamed Solanum laxum but more commonly called “false jasmine”, Solanum crispum, another luxuriant liana, and Solanum rantonetii, often called “Gentian tree” because of the intense colour of its blue-violet flowers: very floriferous, it is widely cultivated.

These species have produced interesting cultivars with white or ultramarine-blue flowers.

Impossible to forget Solanum pseudocapsicum, better known as the “Jerusalem cherry” or “pommier d’amour”, with its round, fleshy fruits resembling small tomatoes in orange, yellow or red.

All are tender and can only be grown in ground where frost is absent. They are classic features of Mediterranean gardens. In more continental regions, they are easily grown in a large pot and brought indoors for winter.

With a very vigorous growth habit, this rambling climbing plant, once established, produces long flexible shoots, almost voluble, that climb over any support. Size varies according to Solanum species.

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

Solanum rantonetii forms a bushy shrub with often trailing shoots and offers a less vigorous development: it won’t exceed 2 m in height and typically produces a highly ramified silhouette at maturity.

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

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

The more or less flexible and drooping shoots carry an elegant, luxuriant foliage reminiscent of jasmine. The foliage is evergreen to semi-evergreen in mild climates but can be deciduous if exposed to frost. The leaves, arranged alternate along the stems, are oblong to lanceolate, or strongly pinnate, sometimes divided into 3 or 5 lobes or bearing lobed leaflets, often with undulate margins. Ranging from 2 to 25 cm long depending on species, they may be glossy or downy.

From bright green to dark green, they sometimes redden in cold weather. Some cultivars bear splendid variegated foliage with cream.

This luxuriant vegetation forms an elegant backdrop to the flowering. Solanum is prized for its flowers and decorative fruit.

The plant is covered with a multitude of small flowers that renew continuously from May until first frosts. Flowering can last up to eight months in frost-free regions. The 5-petalled flowers are bell-shaped, widely trumpet-shaped or more often small star-shaped, typical of Solanaceae (hence its nickname “Star of Bethlehem”).

Solanum jasminoides ‘Album’

They measure 1 to 6 cm in diameter and open in numerous small clusters, sometimes umbel-like or paniculate, 2 to 15 cm across, at the axil of leaves or at shoot tips.

Often characterised by a gentian-like violet-blue, some cultivars produce very bright light blue or a pure white shaded by a cluster of prominent yellow-orange stamens.

Lightly scented, the flowers give off a delicate jasmine fragrance. After flowering they develop into fruits, small toxic berries if ingested, round or ovoid, violet, red, vermilion, orange or yellow and 1 to 2 cm in diameter. This decorative fruiting is, however, rare in our climate.

Fortunately, Solanum pseudocapsicum, mostly grown as a seasonal houseplant, allows enjoyment of this decorative fruiting that lasts through autumn and much of winter when the shrub is kept warm or grown outdoors in a mild climate. Dotting the plant like cherry tomatoes or small oranges, they start green, turn yellow then orange and become bright red when ripe. They have earned this Solanum species the nicknames Jerusalem cherry and florist’s orange.

Like jasmine, Solanum is quite tender, rarely tolerating temperatures below -5 °C / -8 °C. Easy to grow in ground in very mild winter regions, it is a staple of Mediterranean gardens but can adapt as far north as the Paris region in very sheltered spots. Elsewhere, in cold climates, it must be grown exclusively in pots and wintered frost-free, like an orangerie plant.

It needs warmth and sun as well as a fertile, cool but very well-drained soil.

Solanum rantonetii with sumptuous intense blue-violet flowers

This rambling liana readily scrambles up a wall, trellis or pergola. Untrained and left free, it can also form a magnificent, somewhat tangled groundcover.

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

Main species and varieties

There are over 1,400 species of Solanum, including classic Solanum jasminoides with star-shaped white, blue or violet flowers and Solanum crispum, the hardiest of the Solanums — two vigorous but tender lianas. solanum rantonnetii, ‘the gentian tree’, is a more shrubby species with flowers of an extraordinary gentian-blue!

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

Perfect to collect in garden or to grow year-round in conservatory!

Most popular

Solanum jasminoides Blue

A slender, evergreen liana in mild climate. With rapid growth, very floriferous, to train against a wall or to let it climb on wire mesh or a fence.

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

See the product sheet

Solanum crispum Glasnevin

It produces tirelessly a multitude of mauve flowers. It is the hardiest of the solanums! It climbs trellis, arch, arbour, stair railing... It is also grown in a pot on a terrace in the coldest 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 to -5°C, it is very well suited to Mediterranean climate. Elsewhere, it should be grown exclusively in a pot and overwintered frost-free during winter.

• 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 remained very frost-sensitive. Not hardy, it does not tolerate severe frosts. It is easy to grow in ground in Mediterranean or coastal regions, as elsewhere its hardiness will be severely tested.

Foliage is destroyed by cold from 0°C–2°C, while its stump only weakly survives down to -5°C. Some are hardier than they appear, sometimes surviving down to -8 to -10°C in well-sheltered situations under a thick protective mulch, with the stump reshooting in spring without difficulty.

In regions with harsh winters, north of the Loire, grow Solanum in a large container kept sheltered on a terrace and bring it indoors for winter, safe from frosts.

It needs heat and sun: provide a very sunny position, sheltered from draughts. In hot climates it prefers partial shade rather than blazing sun that scorches its flowers.

Once established it is tolerant of summer drought and can cope with ordinary, even slightly calcareous, soil provided it is always perfectly drained. However, it prefers fertile, deep soils in which it can truly flourish.

Solanum can be used in countless ways in a mild-climate garden to flower an arbour, twine around a tree, dress a well-exposed wall, a trellis or a wire fence… What joy when it provides welcome shade after covering a pergola! Foliage remains semi-evergreen in mild climates: a significant asset when masking an unsightly wall or façade. Untrained, it forms an elegant groundcover.

This liana with woody climbing stems needs an airy position as growth is rapid from the first year after planting.

Some Solanum, 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 sheltered on a balcony or terrace; bring it inside to protect from frost in cold regions. For “love-apples” grown indoors, place near a window but not in scorching sun.

When to plant Solanum?

Planting Solanum is done in spring from March to May after last frosts, as this plant is frost-tender. In the meantime, 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, vigorous growth of Solanum, 1 plant per m² will be sufficient as it can spread 3 to 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 bed of gravel or clay pebbles to aid drainage
• Mix a little well-rotted compost into the excavated soil
• Position the plant with the base of the stems level with the soil
• Fill the hole
• Firm gently
• Water thoroughly
• Mulch the base to keep soil cool in summer
• Train branches onto the support

How to plant Solanum in a pot?

Potting mix must be very free-draining to avoid waterlogging the roots of Solanum.

• In a large terracotta pot, place a good drainage layer (gravel or clay pebbles) up to one-quarter of the pot’s 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 sheltered from cold but in light, in a conservatory or cool greenhouse

→ Find out more about growing Solanum in a pot in our care guide!

Maintenance, pruning and care

Solanum needs little care once established. Sunlight and regular watering are the secrets to ensuring good growth.

In open ground

Water regularly and thoroughly during first year after planting to support establishment. Thereafter it will withstand drought well and will only require occasional watering in summer to support flowering.

Solanum is fairly greedy and needs fertile soil to improve flowering. It appreciates regular fertiliser applications during growth, especially in poor soil. A top dressing of compost by raking in in spring and summer will encourage and prolong flowering.

Train new shoots as they develop. Remove faded flowers regularly, which will encourage renewal of flowering.

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

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

In pots

The Solanum grown in a pot must be watered more regularly. Water regularly without letting the rootball dry out when hot. During growth, water once to twice a week and apply a liquid fertiliser twice a month. Reduce watering in winter to every 15 days and stop all feeding.

Spray foliage often with soft water if you want to keep Solanum in pots indoors year-round, as foliage and flowers wilt quickly when air 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 sheltered from winter frosts in a cool greenhouse or conservatory where temperature will not fall below 10°C. You can take them back outside in spring when temperatures have warmed and frosts are definitively over.

→ Find out 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 truly essential, but it can be useful to contain its growth!

With Solanum jamsinoides and crispum, it simply involves controlling spread, removing frail or damaged branchlets and balancing the branches to restore a neat rounded habit.

Solanum tends to be vigorous but tolerates pruning well, even severe pruning, and is not harmed by being cut back every year.

• Prune every year in spring, early March.
• Cut stems back to three to four buds (about 30 cm above ground) and remove old branchlets and broken stems.
• You can also refresh the liana throughout the season without problem to control crowding 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 kills it after a year.

Training a Solanum as a standard

Solanum rantonnetii, or “gentian tree”, can easily be trained as a small standard shrub by pruning lower branches.

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

How to train Solanum?

Stems of Solanum have no tendrils, so they must be trained by tying to a support as soon as planted in ground or into a pot. Supports are varied: Solanum can lean against a wall, cascade over a low stone wall, twine around a tree, climb a wire fence or a trellis.

On a smooth wall: fix hooks and stretch nylon wires horizontally every 50 cm to guide the stems.

Possible diseases and pests

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

Presence of aphids is sometimes visible on leaves. Spray soapy water.

Multiplication

Le Solanum multiplies easily by herbaceous stem cuttings between April and June. Layering is also possible, although more tedious.

How to propagate a Solanum?

Solanum cuttings will flower from the following summer.

• Using pruning shears, take cuttings of 5 to 8 cm, supple, green and without flowers
• Remove lower leaves
• Insert the cuttings into buckets filled with potting compost, turf and sand
• Firm down and water
• Regularly moisten the substrate with a spray bottle
• Place the pot in partial shade under shelter, frost-free in winter at a temperature between 10 and 15 °C in the greenhouse or conservatory
• Plant out in open ground or repot each cutting individually the following spring

By layering

Layering Solanum carried out at the end of autumn produces rooted layerings 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 towards the soil
• Remove lower leaves
• Score the bark for about 3 to 5 cm on the parts to be buried, at a node
• Bury one or several sections 15 cm deep to encourage rooting
• Secure the layerings in the soil with metal pegs driven into the ground
• Cover with potting compost, firm down and water
• Thereafter, water when the soil is dry
• One year later, the following autumn, separate the layerings from the parent plant; they will be sufficiently rooted: cut the stems where they enter the ground
• Replant the layerings in open ground in their permanent position or into pots

Associate

Slender and of rare elegance, Solanum flourishes in gardens of various styles, lending them charm and poetry. It is a staple of blue or white romantic gardens. Above all, it is a classic of Mediterranean and exotic gardens, where it brings a great deal of freshness in summer.

While Solanum does well on its own on a trellis or a fence, it also appears in fresh, romantic combinations with climbing roses and other beautiful climbers such as clematis, honeysuckle, jasmine, passionflower, a trumpet vine (Campsis radicans) or Podranea ricasoliana.

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

In Mediterranean gardens, 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 the feet of Mexican orange, Abutilon or tree mallow.

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

→ Discover more ideas for pairing Solanum