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Purple lisianthus flowers.
Popular as a cut flower, and ideal for cutting gardens, lisianthus adds an air of elegance to the summer garden in warm temperate and sub-tropical regions, with blooms in shades from white through pink and mauve to vivid blue. Lisianthus can be tricky to grow, and it's not a plant for cool to cold areas!

What you need to know about lisianthus

Name: Lisianthus, prairie gentian (Eustoma grandiflorum).

Height: from 60–90cm, reaching maximum height during flowering. 

Foliage: mid-green to grey-green.

Climate: warm temperate to sub-tropical; glasshouse-grown for the florist trade in cooler areas.

Soil: rich loam with a pH between 6.5 and 7; will not tolerate moderate to high acidity.

Position: dappled or light shade, especially in areas with hot afternoon sun.

Flowering: single or double rosette flowers in white, pink and blue, some bi-colours; may last 2–3 weeks in a vase.

Feeding: controlled-release fertiliser at planting and regular applications of water-soluble or liquid fertilisers through the growing and flowering period.

Watering: keep moist but not wet; over-watering may cause fungal diseases.

Appearance and characteristics of lisianthus

Lisianthus is a colourful flowering annual that enjoys warm, sunny conditions. It starts as a compact seedling with mid to grey-green leaves, and then develops tall, slender, multi-branching stems that produce masses of distinctive lisianthus flowers.

The fineness of the stems means the plants are brittle, and can be easily damaged by strong winds. Planting them close together for support or staking is essential. There are some dwarf varieties available that don't need staking—these are ideal for growing in pots.

The petals in flower buds appear twisted, untwirling as they open to form beautiful rosette blooms. Lisianthus flowers look delicate, but will last in a vase for two to three weeks with regular water changes.

Deep blue hues of a flowering lisianthus

How to grow lisianthus

Lisianthus can be raised from seed, but it is a very slow process—it may take close to six months for the seedlings to be large enough to plant out. That means sowing seeds before the coldest months of the year so they will be ready to transplant in spring. Unless you live in the tropics or have a heated glasshouse, this amounts to “mission impossible”. Instead, buy seedlings or bloomer pots (advanced seedlings with flower buds already present)—that way, you can enjoy beautiful white, pink, purple and blue lisianthus flowers from the start!

Lisianthus has a reputation for being tricky but, as with most plants, if you give it what it needs, it will grow and flower well.

  1. Wait until all danger of frosts has passed, in mid-spring, before planting out.
  2. Choose a sunny spot.
  3. A rich, moist but free-draining soil is essential.
  4. Check the pH before planting: 6.5–7 is ideal; add garden lime if the pH is below 6.5.
  5. Work in a controlled-release fertiliser at planting to maximise flowering.
  6. Space plants about 15–20cm apart.
  7. For taller varieties, hammer in appropriately sized stakes for support.

Caring for lisianthus

Lisianthus plants do not like to dry out—make sure the soil is kept moist at all times, but never wet. During hot spells, water early in the morning. If you need to water again in the evening, be very careful to keep the plants themselves dry, as they are very susceptible to fungal diseases that spread rapidly in high humidity or when the leaves are wet.

Being annuals and flowering freely, growing lisianthus plants need a plentiful supply of nutrients throughout the growing season. In addition to the controlled-release fertiliser added during soil preparation, apply a water-soluble or liquid plant food at label strength every three to four weeks to ensure your lisianthus plant remains healthy and vigorous

Lisianthus diseases and pests

Mildews, rusts and other fungal diseases can be troublesome during warm to hot humid conditions. Good air circulation around the plant will assist in eliminating them, but this isn’t always possible when plants are grown close together for mutual support. If required, an application of general-purpose garden fungicide may prove helpful.

Insect pests like aphids and thrips may appear from time to time. Unless they are in plague proportions and are damaging flowers, treatment is not necessary. If required, apply an insecticidal soap or pyrethrum spray.

If you like this then try

Impatiens: bright, flowering annuals that produce colourful carpets of flowers in warm to sub-tropical areas.

Bougainvillea: a vibrant-flowered climber that thrives in temperate to tropical climates.

Poinciana: flame tree with fern-like leaves and masses of scarlet flowers; best grown in tropical and sub-tropical areas.

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