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What is Ruellia?

J.M. Densing
J.M. Densing

Ruellia refers to a genus of flowering plants also known as wild or Mexican petunias. This plant strongly resembles the petunia, although the two are not closely related. There are many different species that are available in a variety of different colors. It grows freely in the wild in warm climates and spreads extremely quickly when conditions are right. It is also cultivated for garden use and doesn't require much care to thrive.

The genus Ruellia does not have a specific native area of origin and species originated all over the globe, mainly in warm sub-tropical to tropical climates. It is most common in Africa, Asia and the Americas. A few species are able to thrive in temperate climates as annuals. The plants grow best in high levels of heat and may grow out of control and becoming invasive under the right conditions. The rapid spread of invasive growth can crowd out other plants that were already established in the area. Some gardeners consider Ruellia a nuisance because of these tendencies, while others enjoy the ease of care.

Man mowing the grass
Man mowing the grass

Most Ruellia species are evergreen perennials, with a blooming season that usually lasts from late spring until fall, but some go year round. Height can vary depending on species, ranging from 8 to 48 inches (20 to 122 cm). The leaves are usually dark green, smooth, and have a long ellipse shape with a pointed end. The flowers strongly resemble true petunias, with a trumpet-like shape that flares out into distinct petals. The flowers come in a wide array of colors including purple, red, pink, blue, and white.

Common uses for Ruellia in the garden include borders, containers, flower beds, and greenhouses. Some types are also used in bog gardens or planted near the edges of ponds. It thrives in extremely moist soil, but it will tolerate drought conditions if they occur. It should be planted in part or full sun and watered at least twice a week. It will produce more flowers in the sun than in the shade, and will spread more readily in moist conditions. It can be propagated, or reproduced, easily using cuttings and will often self-seed without any intervention.

When used in the garden, care need to be taken with Ruellia to ensure that it does not push out other garden plants. When it self-seeds, the seeds tend to travel several feet, contributing to rapid spreading. It may need to be thinned out if the spreading is a problem, however gardeners may enjoy having large areas of the low maintenance, flowering plants.

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