Mexican petunia

Sun

Full sun to partial shade; flowering is strongest in full sun.

Water

Keep evenly moist while establishing. Established plants tolerate short dry spells as well as wet ground; water containers when the surface begins to dry.

Soil

Adaptable to sandy, loamy or clay soils, including periodically waterlogged ground. Use a free-draining potting mix in containers, especially when overwintering indoors.

Height

3-4 ft (0.9-1.2 m)

Spread

2-3 ft (0.6-0.9 m) initially; spreading rhizomes can form much wider colonies

Flowers

Purple to violet-blue flowers from late spring into autumn; flowering may continue much longer in frost-free climates. Cultivars also have pink or white flowers.

Foliage

Evergreen. Opposite, narrow, lance-shaped dark green leaves on upright green to purplish stems.

Growth

Fast in warm weather

Care needed

High

• Pollinators
• Heat tolerant
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Hard

Toughness

Fairly tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   2.2 ft (0.68 m)

3. After 2 years

   3 ft (1.1 m)

   full size

About 2 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Invasive in

the US and Australia

In the garden

Spreads vigorously: plan to contain it.

Growth rate

Fast

• Check local invasive-plant guidance before planting; choose a non-invasive alternative where this species threatens natural areas.
• Water regularly during the first growing season, then water during prolonged dry spells if flowering slows.
• Feed container plants lightly with a balanced fertiliser during active growth; rich garden soil usually needs no extra feeding.
• Use a thin organic mulch around plants, keeping it clear of the stems.
• Remove unwanted shoots promptly, digging out their attached rhizomes rather than simply cutting the tops.
• Keep containers away from drains and natural waterways, and do not dump seed heads, roots or potting mix in garden waste areas outdoors.

Pruning. In late winter or early spring, cut frost-killed stems back to healthy growth or near ground level before new shoots develop. In frost-free areas, shorten leggy stems in early spring; remove seed capsules before they mature if growing a fertile plant.

Late winter

Check overwintered pots for spider mites and remove dead or damaged stems.

Spring

Plant out after frost danger has passed and the soil has warmed.

Late spring

Apply mulch and begin regular watering for newly planted specimens.

Summer

Inspect for spreading shoots and developing seed capsules; remove both promptly.

Early autumn

Take cuttings if you need to keep plants through a cold winter.

Autumn

Move container plants under cover before frost where winters are too cold for outdoor survival.

• Use in large patio containers for upright foliage and a long display of purple flowers, where local guidance permits.
• Combine with cannas and ornamental grasses for contrasting broad and narrow foliage.
• Plant in repeated groups along sunny borders for a continuous band of summer colour, only where spread can be managed.
• Use a locally recommended sterile selection in warm-climate courtyards; allow space for its continuing rhizome spread.

Garden styles it suits: Modern tropical, Tropical, Modern courtyard, Southern, Mexican hacienda and Luxury resort.

Plant it with: Canna, Daylily, Society garlic, Blue-eyed grass and Gulf muhly grass.

Wildlife: Flowers attract bees and butterflies. In invaded wetlands and waterways, dense colonies can displace native vegetation, so wildlife value does not justify planting it where it is invasive.

• Unwanted colonies and seedlings: remove plants with their rhizomes, collect seed capsules before they burst, and monitor repeatedly for regrowth.
• Spider mites, especially under cover: look for stippled leaves and fine webbing; rinse foliage thoroughly and use insecticidal soap labelled for the purpose if needed.
• Sparse flowering and floppy growth in shade: move to a sunnier position and avoid excessive nitrogen feeding.
• Winter losses in cold or persistently wet pots: provide frost-free shelter, good drainage and much less water while growth is slow.

Not known to be toxic to cats, dogs, horses or people, but species-specific poisoning information is limited. No particular part is established as poisonous; it is not an edible plant, and ingestion should be discouraged.

Where it spreads. Spreads aggressively by rhizomes and explosively dispersed seed. Listed as invasive in Florida and invasive or naturalised elsewhere in the southeastern United States, including parts of the Gulf Coast. It is also an environmental weed in parts of eastern Australia, including Queensland and New South Wales. Avoid planting near wetlands, drains or waterways.

• Carolina wild petunia (Ruellia caroliniensis)

  Usually shorter, with broader, often hairy leaves rather than Mexican petunia's long, narrow leaves.

• Hairy wild petunia (Ruellia humilis)

  A lower-growing plant with noticeably hairy stems and broader leaves; it does not form the same tall, cane-like clumps.

• Garden petunia (Petunia × atkinsiana)

  Has soft, sticky-hairy foliage, branching or trailing stems and usually larger flowers, rather than smooth, narrow leaves on upright stems.

Ruellia honours the French physician and botanist Jean Ruel, while Mexican petunia refers to its Mexican origin and petunia-like flowers, although it is not a true petunia.

Propagation. Divide rooted clumps in spring or take softwood stem cuttings in warm weather. Fertile plants also grow readily from seed, but deliberately raising or sharing seed is inadvisable where the species is invasive. Cultivars should be propagated vegetatively to retain their characteristics.

Accepted botanical name

Ruellia simplex

In the US and Canada

Introduced in Hawaii, the lower 48 states, Pacific Basin, Puerto Rico and US Virgin Islands.

Native range

Argentina Northeast, Argentina Northwest, Bolivia, Brazil Northeast, Brazil South, Brazil Southeast, Brazil West-Central, Cayman Is., Costa Rica, Cuba, Dominican Republic and Ecuador.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.