Introduction

Common Periwinkle Vinca minor and Bigleaf Periwinkle Vinca major are very popular garden ornamentals widely sold in nurseries and online stores throughout North America. They are part of the Apocynaceae family in the Gentianales order of dicots. They produce attractive foliage, lovely blue, lavender, or sometimes pink or white flowers, and they require little maintenance. Of course, other than trying to control them to keep them from spreading into your garden beds, lawns, forest, or other areas, they were not intended to grow. In some areas, these plants are not very invasive, but in other areas, they are quite invasive.

Since they spread only vegetatively, the primary source of invasion is through deliberate human introductions as a garden ornamental that they plant and forget about and allow them to escape. We have so many lovely native groundcovers, just do some research into native groundcovers in your region and plant those instead. Native species require no maintenance, they tend not to be invasive, and they offer added wildlife and biodiversity values that invasive species lack altogether.

Description of Vinca major & Vinca minor

Leaves & Stems of Vinca major & Vinca minor

Both species of Periwinkles are scrambling vines from stolons up to 1 m long from fibrous roots 3 – 8 cm long. Their vertical stems grow up to 30 cm tall and are semi-succulent but become semi-woody at the base (caudex).

The leaves of Vinca major Bigleaf Periwinkle are opposite, semi-evergreen, heart-shaped (cordate) to triangular in shape, and are covered with a waxy coating (cuticle) and tiny hairs. They are 4 – 8 cm long and 2 – 5 cm wide. Sometimes, they have a finely hairy (ciliate) margin; otherwise, they are entire.

The leaves of Vinca minor Common Periwinkle differ from Vinca major in that they are evergreen, glabrous (hairless), more leathery, narrowly elliptic in shape, and are only 2 – 4.5 cm long by 1 – 2.5 cm wide with an entire margin that is not ciliate.

Flowers of Vinca major & Vinca minor

The flowers of both Periwinkle species are violet to blue and each has 5 petals radiating in pinwheel-like angles from the floral tube (they are partially connate).

The edges of the petals are typically slightly fringed and occasionally the petals are even white or pink.

Bigleaf Periwinkle Vinca major has somewhat larger flowers than the Common Periwinkle, but otherwise, they appear very similar.

Fruits of Vinca major & Vinca minor

The fruits of Periwinkles are pairs of slender cylindrical follicles to 5 cm long in Vinca major or 2.5 cm long in Vinca minor.

When the follicles dry, they split open to release 3-5 naked seeds that have no tufts (coma), unlike many seeds released from follicles.

Toxicity of Vinca major & Vinca minor

All parts of the plants are considered poisonous due to the presence of toxic alkaloids, which can attach themselves to the microtubules of the cells and impair their ability to divide, causing cell death.

Periwinkles have been known to poison humans, pets, and livestock. Most wild animals seem to know better than to ingest it; even if it is the only forage material around, most still will not eat it.

Similar Species Vinca major & Vinca minor are Frequently Confused With

There are only two species of Vinca that have been introduced to North America so far. However, there are a few other genera native and introduced that can occasionally be confused for Vinca. They can be differentiated as follows:

• Catharanthus roseus – Madagascar Periwinkle appears superficially similar, but it is an upright shrub that does not have a scrambling habit. Also, its leaves are oval to oblong and 2.5-9 cm long, and they are hairless and arranged in opposite pairs. The flowers are larger, up to 5 cm in diameter, with a very long floral tube. The petals are not at right angles to the tube but may still appear somewhat pinwheel-like in shape. The corolla is also typically various shades of pink or white rather than lavender or blue. It is endemic to Africa but has been widely introduced throughout the southern half of the USA and throughout Mexico.
• Phlox divaricata – native to the eastern USA and Canada, this plant has strikingly similar flowers in the same color and sometimes with a somewhat pinwheel shape to the petals. However, it is not a vine but rather an upright herb 25-50 cm tall. The leaves are opposite but are lanceolate and lack a leaf stalk (petiole).
• Euonymus fortunei – the Fortune Spindle is an evergreen vine occasionally mistaken for Periwinkles. They are native to Asia but are widespread in the USA and Mexico. However, the individual vines grow much longer, to 20 m, and their ovate evergreen leaves are much larger than the Common Periwinkle and are not cordate or triangular like Bigleaf Periwinkle. When in flower, they are hard to mistake for Periwinkle because their flowers are much smaller and are white or greenish-white.
• Hedera helix – Eurasian Ivy is occasionally mistaken for Vinca major. However, its vines grow much, much longer than Vinca major, and its leaves are alternate rather than opposite, and they are typically larger, though occasionally they can have similar shapes. Their flowers are also much different, being numerous tiny greenish-white flowers in an umbel.

Native Distribution of Vinca major & Vinca minor

Vinca major is native to the Mediterranean region of Europe and the Middle East from Spain east to Turkey plus northern Africa.

Vinca minor is native to central and southern Europe from Portugal, France, Holland, and the Baltics, plus eastern Caucasus and Turkey.

Habitat Types Where Periwinkles Are Found

In its native environment, Periwinkles are usually associated with moist, fertile, or moderate soils that are moderately acidic to moderately alkaline.

In North America, it is found in those soil types but has also been found in moderately well-drained soil types, poor soils, and even acidic clays. They grow from sea level up to 2300 m in elevation.

Periwinkles are both found in riparian forests, open forests, grasslands, scrub, and roadsides.

Vinca minor is often found in the understory of successional forests, including mature forest types, while Vinca major is more often found in partially shaded open forests and riparian forests.

Both species can grow in full shade, part shade, and even full sun, provided the soil is moist. In arid climates, both Periwinkles are more restricted to riparian forest understory.

Human Uses of Periwinkles

Periwinkle has been long been used as a ground cover plant as a garden ornamental where it forms dense mats. It has also been used for short hedges and for filling around the bases of trees. Though it rarely remains contained to its original purpose.

The dried leaves, aerial parts, and sometimes the whole dried plant are used to extract medicines that are used to treat a number of different cancers as well as to improve blood circulation, brain function, and cardiovascular disorders.

Vinpocetine is a synthetic nootropic (brain-enhancing) drug derived from vincamine, an alkaloid responsible for much of the medicinal activity of the genus. However, unsupervised medicinal use is not recommended due to the toxicity of the plant, which can make you very ill, cause miscarriages, and possibly even death if consumed in sufficient quantities.

Distribution of Vinca major, Vinca minor in North America

Periwinkles were first brought to North America in the 1700s. It was documented in a review of flora as early as the late 1700s, showing that it was already well established in the eastern USA by then.

In Canada, Vinca major has been recorded in British Columbia. Vinca minor has been recorded in British Columbia, Ontario, Quebec, New Brunswick, Nova Scotia, and possibly Newfoundland (excluding Labrador).

In the USA, Vinca major is found in Washington, Oregon, California, Idaho, Utah, Arizona, New Mexico, Texas, Louisiana, Arkansas, Mississippi, Alabama, Georgia, South Carolina, North Carolina, Virginia, Maryland, Illinois, Kentucky, Tennessee, Ohio, Pennsylvania, New York, and Massachusetts.

In the USA, Vina minor is found throughout the entire eastern USA and most of the southern USA. The only states it has not been reported in yet in the continental USA are Idaho, California, Nevada, Wyoming, Colorado, New Mexico, North & South Dakota, and Oklahoma.

In Mexico, Vinca major so far has been reported in Baja California Norte, Sonora, Sinaloa, Durango, Nayarit, Jalisco, Colima, Michoacan, Oaxaca, Chihuahua, Nuevo Leon, Tamaulipas, San Luis Potosi, Guanajuato, Mexico State, Mexico City, Puebla, Morelos, Veracruz, and Chiapas.

In Mexico, Vinca minor has not yet been reported, but it is located on the northern border of the US in Tucson, Arizona, and San Diego, California, so it will likely be recorded there soon.

Periwinkle, particularly Vinca major, has been introduced on every continent except Antarctica.

How Periwinkles Spread

It is primarily spread through long-distance by deliberate human introductions as a garden ornamental. Despite its invasive status, this is still the primary cause of long-distance spread.

Short-distance dispersal is primarily through vegetative means. Both species spread readily through their stolons which can quickly grow 25 cm or more before producing another rooted node yielding another clone.

Short-distance dispersal also routinely occurs by fragments regenerating out of dumped yard waste. In its native range, ants sometimes spread the seeds, but in North America spreading by seeds appears to be negligible to nonexistent.

Habitats at Risk of Invasion in North America

Riparian forests and canyon bottomlands are most at risk throughout all of North America due to their preference for moist soil types.

States and provinces located next to the coasts are also at high risk due to the presence of moist soils in those areas. In those regions, all land types are at risk, closed forests, open forests, roadsides, waste areas, grasslands, shrublands, and riparian areas as well.

The habitats not at risk of invasion are open deserts and high mountainous areas above 2300 m elevation. Fortunately, due to its inability to spread by seed, this restricts its spread to vegetative spread as long as people stop deliberately planting it in their gardens.

Impacts of Invasion

Both Vinca major and Vinca minor can grow in poor soils and full shade, and both are also allelopathic, giving them a significant competitive advantage.

Allelopathic plants inhibit the germination and growth of plants of other species growing in their vicinity due to how they alter the soil conditions. As a result, both species tend to form dense mats that smother native understory species as well as prevent the germination of new trees and shrubs.

Reductions in species richness, however, varied from location to location. This has resulted in Periwinkle being viewed as a ‘limited invasive’ species that is ‘stable’. This may partly be due to its spread being limited to vegetative growth.

However, I have seen firsthand its invasive nature in coastal British Columbia, Canada, as well as Virginia and Georgia in the eastern US, where it does indeed create monocultures of dense mats that exclude all other vegetation.

In riparian corridors, its ability to reduce native vegetation reduces the available forage for both wild and domestic grazers. This is particularly problematic where it occurs in riparian habitats found in otherwise arid landscapes.

In California, Vinca major is an important year-round host to the bacteria causing Pierce’s disease, which is a serious threat to the vineyards located there.

Potential Benefits of Invasion

Vinca minor and Vinca major provide no wildlife values in North America, and due to their toxicity and tendency to form monocultures, there are no potential benefits of their presence here.

Methods to Remove Vinca major & Vinca minor

As always, prevention is the preferred method of control.

It, like most invasive species, is still widely sold online and in most local garden stores. Do not buy or transport any Periwinkle, and do not plant it in your yard.

If you see them being sold online or in your local garden stores, please inform them of their invasive status and ask them to do their part and cease selling them. Ask them to instead sell more native species as ecologically friendly garden alternatives to invasive species.

Do some research into native ground covers for your area. You will be pleasantly surprised by the number of low to no-maintenance, non-invasive native species that will grow in your area.

Physical Control of Vinca major & Vinca minor

Once already established, however, physical control is always the most effective means. Physical control is labor-intensive and time-consuming, but it usually causes the least amount of environmental damage.

Fortunately, Periwinkle seed production and spread are not an issue, so they can be physically removed at any time of year. Removal is easiest, however, when the soil is moist, as the roots cling less tightly, allowing the plants to be pulled more readily. This means that spring and fall are often the best times, but it depends on your location.

Physical methods to remove Periwinkle generally involve raking up the stolons and then pulling the plants out using hand tools.

When dealing with large infestations, rake it first as this pulls the stolons up, then the mowing macerates the vines. Given their ability to regenerate by fragmentation, this requires repeated treatments throughout the entire growing season and is only recommended for large infestations where hand removal is not feasible.

For smaller infestations raking followed by pulling plants is often sufficient, though, like all control methods, this too will have to be repeated.

Try to pull as many of the roots as possible, but you will not get them all. The starchy roots of the Periwinkles allow them to regenerate following any method of control. As a result, ongoing monitoring is essential.

Solarizing Small Patches

Sometimes a small patch could be solarized by covering it with heavy black tarps and leaving it there in the sun for 4-6 months. This is the least labor-intensive method of control. The area should still be monitored over the next couple of years to be sure that none regenerate. Any that are found can simply be pulled by hand.

Disposal of the Plants Once Removed

Due to their ability to regenerate from fragments, all plants removed should be either burned or solarized. Burning is an easy and efficient way to get rid of plants, but if burning is not allowed in your area, then they should be polarized.

To solarize, put the shrubs under a thick black tarp or into thick black garbage bags and leave them in the full sun for at least 8 weeks to be sure that none of the vines are viable anymore.

Chemical Control of Periwinkle

Chemical applications are almost never an ideal method of control for any invasive species. That is because chemical alteration of the environment often makes the environment more suitable for invasive species than native species.

Furthermore, it is often difficult to keep the chemical control method contained so that it does not directly affect any native species that are there during the application process itself. As a result, plots where chemical control is used usually show a decrease in species richness. On the other hand, in plots where only physical control is used, species riches significantly increases.

Furthermore, there are no chemical control methods that effectively target only Periwinkle. And the starchy roots appear able to regenerate the plants not long after chemical control methods are used so additional control methods will still be required.

Chemical control is not recommended.

Biological Control of Periwinkle

Biological control involves the use of a predator, herbivore, disease, or some other agent to control an invasive species once it is established in the environment. The problem with biological control is that the agent used must be entirely specific to only the target organism before releasing it into the environment. This is often difficult to determine since the agent of control is also not native to the environment and could behave differently when released there. Take the example of the mongoose and the rat. The mongoose was released in Hawaii in the late 1800s to help control the rat. To this day, there are still rats in Hawaii, but the mongoose has helped to decimate many native bird populations.

Biological control methods are extremely risky and should only be carried out by professionals after years of rigorous study. The use of biological control methods can never be used alone. They must be part of an integrated pest management approach.

In the case of Periwinkles, no biological control methods are currently being used. Most animals will not even graze on the plant. Due to its toxicity, it is not even recommended to use goats that eat anything, as it could potentially make them very ill.

Integrated Pest Management & Ongoing Monitoring

Integrated management is always the best approach. In its simplest and least impactful form, this involves physical removal methods, possibly biological control methods, replanting, and ongoing monitoring. Integrated management is required because the area needs to be monitored for returning sprouts otherwise, all the hard work done in removal could be wasted if the invasive species is allowed to regrow.

Replanting With Native Species is Crucial

In all cases of removal, the site should be replanted immediately because the bare soil will allow the Periwinkle or other potential invaders to claim the empty space left behind. A replanting program should already be planned and ready to implement immediately upon the removal of the Periwinkle. In most cases, these will be native understory plants, such as ferns, small shrubs, native vines, etc, that would have grown there before the Vinca species invaded. Find a local nursery that specializes in native species or ethically wildcraft your own from the local environment.

The only instances where replanting is not required are small isolated individuals that have not yet had a chance to form a clonal colony. In this case, simply remove the plant(s) and monitor them to make sure they do not return. Nearby native species should be able to rapidly recolonize the space they were removed from.

Ongoing Monitoring is Essential

In all cases of invasive Periwinkle removal, ongoing monitoring is absolutely essential. Yearly monitoring programs should be put in place to ensure that any surviving individuals are removed so that the population is not able to recover. This is required whether the area is replanted or not.

If yearly monitoring is not put in place to remove young plants before they have a chance to become established, then all your hard work done in the removal process will be wasted if the patch is allowed to regrow.

References and Resources

CABI on Vinca major https://www.cabi.org/isc/datasheet/56402

Canadensys Plant Search https://data.canadensys.net/vascan/sea rch

Dictionary of Botanical Terms – Lyrae’s Nature Blog Dictionary of Botanical Terms

Eflora Plants of North America http://www.efloras.org/browse.aspx?flora_id=1

Fire Effects Information System on Periwinkle https://www.fs.fed.us/database/feis/plants/vine/vinspp/all.html

iNaturalist Plant Search https://www.inaturalist.org/home

USDA Plants Database https://plants.sc.egov.usda.gov/home

Willis, Lyrae (Unpublished).  Plant Families of North America.

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