How to Plant, Grow, and Care For Wild Petunias

Wild petunia (Ruellia humilis) is a wonderful wildflower that you can add to just about any garden layout. These versatile flowers look great in containers and raised beds. They are equally at home in a cottage garden or larger naturalized areas. 

These US-native flowering beauties have a long blooming period to liven up your garden throughout the spring, summer, and fall. They’ll also bring in the pollinators and attract plenty of attention from passers-by. They are medium-sized plants and just the right size to fit into any gardening theme. 

These will reseed each year, so you’ll never be without a few wild petunias. If you are looking for a plant to come back reliably year after year, this is a great choice. You’ll only need one plant to start a population. Once you have a healthy plant, it’s easy to propagate and establish a healthy patch of these colorful flowers.

Now, let’s dig a little deeper to learn more about these wonderful plants and all the ways you can use them to enhance your home garden.

Plant Natural History

Wild petunia is native to much of the central and eastern United States, with the exception of the northern Great Plains States and New England. They grow naturally in prairies and glades, grasslands, along roadways, and along forest edges. In many places throughout their range, they are so common that they are considered to be roadside weeds and even naturally appear in lawns and gardens.

Wild petunias are part of the Acanthus family (Acanthaceae) which contains approximately 2500 species throughout the world. Most of these plants are from tropical regions, although some grow in temperate regions. The wild petunias of the genus Ruellia contain over 300 unique species of often colorful and ornamental plants. 

Characteristics

Wild petunia is an herbaceous perennial wildflower. Each year, these plants form multi-stemmed clusters of upright, leafy stems topped with delicate-looking flowers. Dense clusters have an appealing rounded form. 

The leaves are simple and grow as opposite pairs along the entire length of the stems. Each leaf is an elongated oval, measuring up to three inches long and one inch wide. The leaves stay solid green throughout the growing season and are slightly fuzzy to the touch, being covered with a fine layer of soft, downy hairs. 

Flowers appear in late summer and persist throughout the summer and into mid-fall. The blooms are showy, with a thin, delicate appearance, but don’t let that fool you. These flowers are surprisingly tough, surviving full sun and other harsh conditions. Their pale lilac color is very attractive without being gaudy. 

Each flower has a broadly open face with five petals, narrowing to a thin, trumpet-like tube at the base. Flowers frequently display darker purple stripes within the tubular openings. Individual flowers generally bloom for a single day and then drop off.

Propagation

It’s very easy to propagate wild petunias because they readily propagate themselves. Starting from scratch, you can obtain seeds and start your own plants. If you already have wild petunias in your yard, propagate your established plants by collecting seeds, taking stem cuttings, or dividing larger clusters. Do not dig or remove wildflowers from their natural habitats.

Seed

These petunias are prolific self-seeders. Seeds will germinate best after they have been allowed to cold stratify and rest in moist soil during the winter months. If you are buying fresh seeds to start some new plants, direct sown the seeds in late fall, allowing them to overwinter naturally. 

If you want to start seeds indoors, you’ll need to cold-stratify them. Plan ahead so you can store seeds in your refrigerator for about 70 days before planting. After cold stratification in your refrigerator, sow the seeds in fresh potting soil, covering them with a minimal sprinkling of loose soil. Place the pots or trays in a protected, warm location and keep the soil moist until the seeds germinate. You’ll need some patience here; it can take between four and six weeks until germination. 

After germination, continue to keep your seedlings moist but not wet. Allow them to grow several inches tall before transplanting outside into a permanent location or container garden. Each seedling should have at least two pairs of true leaves before transplanting outdoors. This will make them both easier to handle and a little tougher. 

Cuttings

These are great plants for propagation with cuttings. Using sharp snippers, simply take a healthy stem cutting four to six inches long. Strip off the lower two or three inches worth of leaves and place the stripped section of the stem in a vase or cup of water.

Within a few weeks, the stem will start to develop fine, new, white roots. Allow the roots to grow a few inches, and then transplant your cuttings into fresh soil. This is an ideal way to start new plants for pots and containers. 

Division

It’s easy to propagate wild petunias by division. After a few years, they will develop into large clusters of stems. Divide your clumps in spring or fall. Use a sharp spade to divide the cluster in half, digging out the roots and stems from the half you’d like to transplant. Carefully remove the part of the plant you have separated and continue to follow the instructions for transplanting.

Transplanting

Grab your gardening gloves and plan your transplanting for a cool spring or fall day. First, prepare your container or garden plot by loosening the soil. Dig a hole slightly larger than the container or root ball of the plant that you’d like to transplant.

Carefully remove your plant from its pot and transfer it into the hole. Fill in the gaps around the plant’s roots with fresh soil and tamp it down gently. Water your transplant well to help it settle into its new home, and keep it moist for the first couple of weeks following transplanting. 

How to Grow

Wild petunias are easy to grow. These plants are highly adaptable and well-suited for many varied conditions. Make sure to offer them a location with plenty of sunlight and generally moist soil, and they should perform well with minimal trouble. 

Sunlight

Choose a location with full sun or partial shade. Ideally, your wild petunias should get at least four hours of bright sunlight each day. Plants grown in shadier conditions won’t flower as prolifically as those grown in full sun.

Water

Wild petunias like moist soil, although they are also quite drought-tolerant. You’ll need to water freshly planted seeds and seedlings, but once they’ve become established, it’s unlikely that you’ll ever need to water them again. 

Soil

Wild petunia performs well in average-quality, well-drained soil. These plants are not picky about soil pH or soil quality and will tend to grow well in almost any soil type as long as it’s well-drained.

Climate and Temperature

Wild petunias are hardy perennials in USDA Plant Hardiness Zones 4 – 8. They tolerate cool climates with winter freezes, as well as warm climates with long, hot summers. They don’t do well in temperature extremes; they won’t survive winters in extremely cold zones and will tend to die back during excessively hot summers. However, their roots can survive in these conditions.

Fertilizing

You don’t need to worry about adding fertilizers to your wild petunias. These plants grow well in natural conditions. You can always boost the soil in your flower garden by adding an annual side dressing of organic compost around your plants. As the compost slowly breaks down, it releases nutrients into the surrounding soil. 

Maintenance

Wild petunias generally grow very well without regular maintenance. You will, however, end up with ever-increasing patches of petunias. Help keep your petunia patch looking great by thinning any unwanted seedlings each spring. This will allow more spacing between plants and allow them to look their best. 

Mulch

While mulching isn’t necessary for wild petunias, it does have some benefits. Natural, biodegradable mulches are the best choice. They break down over time and add some nutrients back into the soil.

Mulches also help retain soil moisture and protect plant roots from temperature extremes. Mulching around your plants is aesthetically appealing and helps keep the weed population down.

Garden Design

Wild petunias are a versatile addition to your landscape. They grow well in so many different conditions that it’s hard to find a place where wild petunias wouldn’t add a touch of charm. Grow them in your pollinator garden to help attract butterflies and bees. Their long blooming period will help guarantee there’s always a source of nectar available. 

Use wild petunias in your native plant garden or pocket prairie, surrounded by other colorful and hardy native plants. Their low stature allows you to use these plants as effective borders and edging, growing along a pathway, or placed in odd corners where they can fill in the available space. Wild petunias have good shade tolerance so you can grow them at the edge of a sunny area where they receive some shade, saving the sunnier places for full-sun-loving plants.

If you have limited space available, try growing them in a container on your patio. They have good drought tolerance, making them a great option for containers and rock gardens. If you don’t want to maintain your plants from one year to the next, particularly in planters, wild petunias are easily started from seed each year and grown as annuals.

Varieties

Mexican Petunia, Ruellia simplex

The Mexican petunia is an ornamental wildflower native to Central and South America and is cold-hardy in zones 8 through 10. These purple-flowering plants grow readily from seed and can be used as an annual, but be aware that they spread aggressively in warm climates. This wildflower is listed as an invasive species in Florida. 

Red Ruellia, Ruellia elegans

The red ruellia, also known as Brazilian petunia, is an annual wildflower native to Brazil. This attractive red-flowering plant grows quickly and spreads rapidly by self-seeding. Hummingbirds and butterflies love the long-blooming, tubular flowers.

Carolina Wild Petunia, Ruellia caroliniensis

Carolina wild petunia is a common perennial wildflower native to the southeastern United States. It has a long flowering season, blooming sporadically from spring through fall. The lavender, trumpet-shaped flowers attract pollinators and readily reseed themselves in lawns and gardens.

White Ruellia, Ruellia metziae 

White ruellia is a white flowering species native to native only to Texas. It is well adapted to living in harsh environmental conditions, including dry, gritty soil, and long arid summers. For a plant adapted to thrive in the desert, it’s no surprise that this species thrives on neglect. The white flowers bloom throughout the summer and into fall, attracting butterflies and bees. 

Desert Ruellia, Ruellia californica

Desert ruellia is an evergreen shrub native to southern California and Mexico. This shrub can grow up to five feet tall and thrives only in hot, arid climates. Numerous lavender flowers bloom from spring through summer, providing nectar for pollinators and hummingbirds. 

Wildlife Value

Wild petunia is a good choice for your wildlife-friendly landscape. The flowers attract butterflies, native bees, and other beneficial insects. Wild petunia is a larval host plant for buckeye butterfly caterpillars, so you may see these prickly-looking caterpillars feasting on the leaves. The white peacock butterfly also uses it as a larval host plant. These plants are not bothered by browsing deer.

Common Problems

Wild petunias are generally trouble-free. There are no serious pests or diseases associated with these plants. They are resistant to deer, wet soil, heat, humidity, and drought. The most serious problem you are likely to encounter is that they can spread aggressively by self-seeding. Pull any unwanted seedlings each spring to help control spreading.