Photo: Prenn / CC BY-SA 3.0 / Wikimedia Commons

Ruellia

Ruellia simplex

A tough, upright perennial with petunia-like purple trumpets that flowers through the warm months and tolerates almost anything, which is exactly why it spreads and is listed as invasive in Florida.

Mature size0.3–1.2 m tall, 0.4–1.5 m spreadGrowthFastSunSun/part shadeWaterModerate

Heat: 4 of 5

Salt: 2 of 5

Drought: 3 of 5

Shade: 3 of 5

Ease of care: 4 of 5

Use in a design Get it looked after

Season

Through the Dubai year

How Ruellia behaves through Dubai's seasons, month by month.

JJan

FFeb

MMar

AApr

MMay

JJun

JJul

AAug

SSep

OOct

NNov

DDec

Avg high °C

24°

26°

29°

34°

38°

40°

42°

40°

36°

31°

27°

Best planting window

Oct – Dec

Jan – Mar

Purple, pink or white trumpets, each lasting a day

Mar – Nov

Cut back to renew, and remove old stems

Fresh stems after the cut-back

Light balanced feed

Best planting window: Oct–Mar
Plant in the cool season; use edging or a pot to contain the clump.
Purple, pink or white trumpets, each lasting a day: Mar–Nov
NC State reports flowering from late spring to early autumn; UAE timing is not well documented and follows the warm-season pattern.
Cut back to renew, and remove old stems: Feb–Mar
Remove spent flowers and seed capsules during the season to limit self-seeding.
Fresh stems after the cut-back: Mar–Apr
Light balanced feed: Mar, Jun

In Dubai's mild winters ruellia slows rather than stops, and a late-winter cut-back to a short stubble sets off a flush of fresh stems in March and April. Flowers open from spring through autumn, each lasting a single day, with a fresh set each morning on a well-watered clump. Seed capsules form behind the flowers and burst open when ripe, so removing spent stems through the season limits seeding. In winter growth slows, which is the moment to tidy the clump before the next flush.

Meet the plant

Meet the Ruellia

Meet ruellia, known as Mexican petunia, a plant that cannot be accused of fussiness. It grows in clay or sand, in drought or in a wet patch, in sun or part shade, and from late winter to autumn it sends up purple, pink or white trumpets that look like petunias held on tall, slim stems. Each flower lasts only a day, but the plant replaces them so steadily that a stand always looks in bloom.

That toughness has a second face. Its seed capsules burst open explosively, flinging seed some distance, and underground stems spread the clump outward, so ruellia does not stay where it was put. In Florida it is classed as invasive and University of Florida's assessment finds no recommended use for it. A Dubai garden has fewer wet places for it to colonise, but it will still crowd neighbouring beds and be difficult to dig out.

Contained by edging, or replaced by a sterile cultivar such as 'Purple Showers', it is a cheerful, easy filler. Planted without thought, it becomes a weed you chose.

Ruellia simplex, sold as Mexican petunia, Mexican bluebell, or under older names Ruellia brittoniana and Ruellia tweediana, is a perennial from Mexico and Central and South America. The Florida Natural Areas Inventory describes it as growing to about a metre tall, with dark green, lance-shaped leaves and purple, pink or white trumpet flowers 4 to 8 cm across. NC State Extension notes that each bloom lasts one day, and that in cultivation the plant is more often 60 to 90 cm tall. In Dubai it is used as a mass planting, a border or a container filler through the warm months.

Its tolerance is unusually broad. NC State reports that it thrives in boggy conditions and in drought once established, in sun or part shade, and in clay, loam or sand, whether acidic or alkaline. That breadth is also the problem. Seed capsules of 4 to 28 seeds burst open explosively, the seeds becoming sticky when wet, and rhizomes spread the plant underground. University of Florida classes it as invasive in all regions of Florida with no beneficial uses, and the Florida Natural Areas Inventory lists it as a Category 1 invasive on the Florida Invasive Species Council's list.

In a desert city the risk to natural areas is lower, but the garden problem is the same: it escapes edging, seeds into lawns and neighbouring beds, and removal means digging out the whole root system. University of Florida recommends buying only a sterile cultivar such as 'Purple Showers', or a native Ruellia, and asking the nursery which variety is being sold. Used with edging and deadheading, it is a colourful, undemanding filler.

Design

Where to use it

Mass plantingLow borderContainer fillerMoist-bed accent

Use ruellia where its spreading habit can be contained, such as a bed bounded by paving or deep edging, or a large pot. It suits a moist, sunny spot where little else will thrive, and where its purple can sit against broad tropical leaves. Keep it away from a lawn edge or a bed of finer plants that it could swamp, and plan to remove spent stems before seed capsules ripen.

Heliconia

Heliconia's bold, upright bracts and ruellia's soft purple trumpets share the same moist, tropical conditions and give contrast in texture.

Elephant ear

Elephant-ear's huge leaves suit the same moist bed and give a strong backdrop to ruellia's slim stems and small purple flowers.

Hibiscus

Hibiscus's large flowers and ruellia's smaller trumpets both want regular water, so they share an irrigation zone easily.

Care guide

How to grow it in Dubai

Watering: Summer: Moderate: it tolerates both drying out and wet soil once established, but looks best with regular deep watering in the heat.
Winter: Reduce frequency as growth slows.
Establishment: Water regularly until the clump has rooted and begun to spread.
Soil: Adaptable: NC State lists clay, loam and sand, acidic or alkaline, and good drainage to occasionally wet.
Feeding: A light balanced feed in spring and early summer is enough; heavy feeding mostly adds leafy growth that must be cut back.
Pruning: Cut back hard in late winter to renew the clump. Remove spent stems and seed capsules through the season, since the capsules burst open and scatter seed.
Planting: Plant October to March in sun or part shade. Contain it with deep edging or a pot, and ask the nursery whether the plant is a sterile cultivar such as 'Purple Showers'.
Pests: Generally trouble-freeSouthern blight in wet, warm conditions (occasional)

Avoid these

Common mistakes

Planting it beside a lawn or a bed of finer plants without edging. Rhizomes and self-sown seedlings will find the gap, and it is far easier to contain on day one than later.
Assuming a dwarf or compact variety will not seed. University of Florida identifies only a few sterile cultivars such as 'Purple Showers', so ask the nursery which variety is being sold.
Letting spent flowers and seed capsules build up. The capsules burst open when ripe and scatter seed, so removing spent stems regularly limits spread.
Planting it as a quick fix in a spot you may later want to replant. Removing an established clump means digging out the entire root system.

Extra notes

Good to know

University of Florida's assessment classifies Mexican petunia as invasive in all regions of Florida, with no beneficial uses; the Florida Natural Areas Inventory records it as Category 1 on the Florida Invasive Species Council's list. The concern is natural wetlands and woodland, which Dubai largely lacks, but the plant's behaviour is the same.
NC State Extension also lists it as invasive in South Carolina, Texas and Hawaii, and notes removal can be challenging from a home landscape.
Its seeds develop a gel-like coating when wet, which lets them adhere to surfaces as they dry; the capsules hold between 4 and 28 seeds.
UF/IFAS tested 'Purple Showers' and found it non-invasive, which is why extension advice points gardeners to that cultivar in Florida.

Toxicity: No toxicity is reported in the sources consulted.

Pros

Petunia-like purple, pink or white flowers through the warm months
Tolerates heat, drought once established, and wet soil
Adapts to clay, loam and sand, acidic or alkaline
Few insect or disease problems reported
Easily cut back in late winter to renew the clump

Cons

Spreads by explosive seed capsules and underground rhizomes into neighbouring beds
Classed as invasive in Florida, and listed as invasive in South Carolina, Texas and Hawaii
Each flower lasts only a day
Hard to remove once established; the whole root system must be dug out
Fertile cultivars still seed; check which variety you are buying

FAQ

Common questions

Is ruellia invasive in Dubai?

It is listed as invasive in Florida and other warm regions because it spreads by explosive seed capsules and underground rhizomes into natural areas. Dubai has few wet natural habitats for it to invade, but it can still spread into neighbouring beds and be hard to remove, so use edging.

How can I stop ruellia spreading in my garden?

Contain it with deep edging or a large pot, remove spent flowers and seed capsules through the season, and cut it back hard in late winter. Pull any self-sown seedlings early.

Is there a non-invasive ruellia?

University of Florida identifies 'Purple Showers' as a sterile cultivar that has been tested and found non-invasive. Ask the nursery which variety you are buying, because plants are often sold under the generic name.

Why do the flowers only last a day?

That is normal for the species: each bloom opens in the morning and fades within about a day. A well-watered clump produces new flowers daily, so the plant still looks in bloom.

What can I plant instead for purple colour in a small bed?

A sterile cultivar such as 'Purple Showers' is the closest match. For seasonal colour without any spread risk, Petunia gives purple and pink through the cool months, and Plumbago gives a taller, softer blue shrub.

Not sure how it suits your garden?

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