Mexican Petunia

Ruellia coerulea

Leisure and Cultural Services Department

“Jockey Club One Person, One Flower” Scheme

2016/17

116mis\[D9-2]OPOF 2016-17 翠蘆莉(E)

Mexican Petunia

Scientific Name: Ruellia coerulea

Common Names: Mexican Petunia, Mexican Bluebell,

Britton’s Wild Petunia

Family: Acanthaceae

Genus: Ruellia

Place of Origin: Mexico

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Form and Characteristics

Distribution:Tropical and subtropical regions

Species: There are tall and dwarf cultivars with the latter

characterised by dense clusters of leaves.

Flower Colour: Pink, purple, violet, white, etc.

Flowering Period: Summer to

autumn, with summer being

the peak season.

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Form and Characteristics

• A renascent herbaceous perennial

• An erect plant that stands 30 to 70 cm in

height with a similar spread.

• It has rhizomes from which new shoots can

develop.

• The fleshy stem, reddish brown to dark purple

in colour, is slightly quadrangular, grooved and

usually lignified at the base.

• Its dark-green leaves, about 8 to 20 cm long,

are simple, opposite and linear-lanceolate, and

have purplish-red veins and petioles.

• The flowers grow in axillary cymes and resemble

Petunia with their blue to violet funnel-shaped

corollas.4

Form and Characteristics

• Flowers open in the morning and fade by dusk, lasting only

one day.

• Each flower usually develops into a capsule (except for

some cultivars).

• The long, ellipsoid capsule is about 2.5 to 3 cm in length.

Containing 12 to 20 seeds, it splits open lengthwise when

mature.

• The flat, round, brown seeds (about 0.2 cm

in diameter) are covered

with soft hygroscopic hairs.

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Growth Habits

• The plant prefers a warm tropical climate and full sun, with

an optimum growth temperature of 20˚C to 30˚C.

• It can cope with partial shade.

• Direct exposure to sunlight encourages maximum flowering

and the extent of flowering may be dependent on the

amount of light it receives.

• The above-ground parts of the frost-intolerant

plant wither in the freezing winter; as

temperature rises, however, new shoots grow

from the underground rhizomes.

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Growth Habits

• The plant is not particular about soil. It thrives in

humus-rich, well-drained soil.

• It can grow in clay or sand.

• It is very drought-tolerant and can get by with little

watering.

• It can adapt to soggy or waterlogged soil.

• Soil moisture should be controlled during the growing

season for optimum bloom.

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Plant Care

• The plant needs little pruning in general.

• Heavy pruning to an aged plant with a woody base

after the flowering period can help resume vigorous

growth.

• Application of fertiliser in an appropriate amount after

pruning can induce new shoots and encourage healthy

plant growth.

• Pruning the stems after the flowers wilt can promote

growth of new buds and reduce wastage of nutrients.

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Propagation – Seed Sowing

• Mexican Petunia is largely propagated by seeds. Sowing can be carried

out in spring or autumn.

• The optimum temperature for germination is between 22°C and 25°C.

• The seeds should be covered with a thin layer of soil after being

sowed. Keep the growing medium moist and the seeds will germinate

in 7 to 10 days.

• The nursery tray can then be relocated to a brighter area under

subdued light. The seedlings are ready for transplant in about 5 to 6

weeks when 4 to 6 young leaves have emerged.

• Given a suitable environment, flowers will bloom about 8 to 10 weeks

after the seedlings are transplanted.

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Growing Medium for Seed Sowing

• Peat moss, Vermiculite, Perlite (1 : 1 : 1)

• Subsoil, Peat moss, River sand (1 : 1 : 1)

River sand Perlite Peat moss Vermiculite

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Propagation – Soft Tip Cutting

• Cutting can be carried out in spring or autumn.

• The rooting medium should preferably be well-aerated, properly drained and clean sandy soil.

• The optimum temperature for cutting is between 22°C and 24°C.

• Select healthy and sturdy soft tips without flower buds as cuttings, each of which should be 10 to 12.5 cm long.

• Each cutting should have at least 3 to 4 nodes and preferably short internodes.

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• Strip all but the top 3 to 4 leaves and insert the

bottom one-third to half of the cuttings into

the medium.

• Water the mixture thoroughly, then leave the

cuttings in a partially shaded place for around

one week before moving them to a brighter area

under subdued light. Keep the medium moist

throughout the period.

• Roots begin to develop in about 2 weeks and

cuttings with vigorous root development can be

transplanted for establishment.

Propagation – Soft Tip Cutting

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Growing Medium for Potting

River sand Perlite Peat moss Vermiculite

• Black topsoil, Peat moss, Subsoil (2 : 1 : 1)

• Peat moss, Perlite, Vermiculite (1 : 1 : 1)

• Subsoil, Peat moss, Perlite (2 : 1 : 1)

• Subsoil, Peat moss, Vermiculite (2 : 1 : 1)

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Potting up• The seedlings are ready for transplant after 4 to 6 true leaves

have emerged.

• The plant needs little pruning in general. To promote the growth

of more lateral buds and flowers, you may consider pinching.

• Transplant the seedlings into a pot with a diameter of 13 cm.

• Water the plant immediately after transplant.

• Keep the transplanted seedlings in a semi-shaded place for 2 to 3

days to protect them from direct sunlight.

• After that, place the seedlings under sunlight for 8 to 10 hours a

day to encourage growth and flowering.

Handling of Seedlings

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Watering

• Soil with adequate moisture is essential for healthy

root growth in a newly repotted or transplanted

plant.

• Once the plant is established, it requires little

fertiliser and water.

• Keep the growing medium well-drained.

• Soggy or waterlogged soil will result in poor

growth and even root rot.

• Water the plant when the topsoil gets dry.

Handling of Seedlings

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Light and temperature

• Keep the transplanted seedlings in a semi-shaded

place for 2 to 3 days to protect them from direct

sunlight.

• Abundant sunlight is required for exuberant growth.

• Place the seedlings under sunlight for 8 to 10 hours a

day.

• Insufficient exposure to sunlight will result in

poor flowering.

• Optimum growth temperature is 20˚C to 30˚C.

Handling of Seedlings

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Fertilising

• When potting up or repotting seedlings, organic matter or

slow-release chemical fertilisers may be used as a base

fertiliser.

• Apply fertiliser once every 3 to 4 weeks during the growth

period. Frequent light applications are preferred.

• Application of fertiliser in an appropriate amount after

pruning can encourage healthy plant growth.

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Fertilising

• Apply chemical fertilisers containing nitrogen(N),

phosphorous(P) and potassium(K) (Fast-release

fertiliser).

• The ratio of nitrogen, phosphorus and potassium

should be 10 : 30 : 20.

• Avoid excessive use of nitrogen fertiliser (which

stimulates leaf growth) as it will lead to the overgrowth

of stems and leaves and hamper flowering. The

branches, becoming too tall and soft, may easily topple.

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Prevention and Treatment of

Pests and Diseases• Mexican Petunia is rarely affected by pests or diseases.

• Keep the soil well-drained and avoid over-watering.

• Apply only the appropriate amount of fertiliser.

• Loosen the soil and weed regularly.

• Ensure sufficient light and space for the plant.

• Keep the growing environment clean and

well-ventilated.

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Horticultural Application

• Floral display / Garden

• Edging plant

• Ground cover

• Nectar plant for insects

• Bog garden

• Pond garden

• Household greening

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Points to Note

• Keep the plant in a shaded, cool and well-ventilated place to

protect it from the scorching heat.

• As the fruits crack when mature, it is advisable to pluck or snip

the browned fruits before they crack. This will prevent the seeds

from spreading all over and growing into weeds.

• To carry out horticultural maintenance properly, please wear

gloves when handling plants and wash hands afterwards.

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The information leaflet, planting demonstration and

presentation materials on Mexican Petunia will be

uploaded to the following webpage in due course:

http://www.lcsd.gov.hk/en/green/education/

greeningschool/one.html

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