Horticulture Magazine

Verbena Bonariensis

purple verbena bonariensis flowers
By CHRIS LEE
Chris Lee, MA - Gardening Writer

Chris is a gardening writer and nature enthusiast. He graduated from Oxford Brookes University in 2022 with an MA in Psychology. Chris works with the Leeds Green Action Society, helping their food cooperative by growing various fruit and vegetables on their two allotments in Hyde Park, Leeds.

/ Updated August 29th, 2023
Reviewed By COLIN SKELLY

Colin is a Horticulturist and Horticultural Consultant with experience in a range of practical and managerial roles across heritage, commercial and public horticulture. He holds the Royal Horticultural Society’s Master of Horticulture award and has a particular interest in horticultural ecology and naturalistic planting for habitat and climate resilience.

/ Meets Our Editorial Guidelines

Verbena bonariensis is a perennial purple-topped plant that not only looks great but is also quite easy to grow and look after.

Adding these plants to your garden will help to give it a unique look and add plenty of colour.

You can buy V. bonariensis in containers or grow them yourself from seeds.

Each approach has its advantages, but providing you take care of your plants properly, they should thrive and last for many years regardless of which option you choose.

Overview

Botanical NameVerbena bonariensis
Common Name(s)Purple Top, Argentinian Vervain
Plant TypePerennial Flower
Native AreaSouth America
Hardiness RatingH4
FoliageSparse, oblong leaves
FlowersSpikes or panicles of small purple flowers
When To SowMarch, April, May
Flowering MonthsJune, July, August, September
When To PruneMarch
Sunlight

Preferred
Full Sun

Exposure
Exposed or Sheltered

Size

Height
1.5 – 2.5M

Spread
1.5 – 2.5M

Bloom Time
June – September

Soil

Preferred
Most Soil Types

Moisture
Moist but well drained

pH
Any

V. bonariensis is part of the Verbena family and goes by many names, including Purpletop Vervain, Tall Verbena, Argentinian Vervain and Pretty Verbena.

It’s native to South America, but today it is grown in many different parts of the world.1Mahr, S. (n.d.-m). Verbena bonariensis. Wisconsin Horticulture. Retrieved March 27, 2023, from https://hort.extension.wisc.edu/articles/verbena-bonariensis/

lilac flowering umbels of verbena bonariensis with white hydrangea in the background

Because of its propensity to self-seed, it is considered an invasive species in some areas.2Verbena bonariensis (clusterflower vervain). (2022). CABI Compendium. https://doi.org/10.1079/cabicompendium.56181

For example, in Washington state, it’s on the invasive species list.3Tall Verbena. (n.d.). Washington State Noxious Weed Control Board. Retrieved March 27, 2023, from https://www.nwcb.wa.gov/weeds/tall-verbena

There are also certain places where it’s considered to be a weed, including Australia, New Guinea and Fiji.4Sweet, L. (2016, September 20). Verbena bonariensis Risk. California Invasive Plant Council. Retrieved March 27, 2023, from https://www.cal-ipc.org/plants/risk/verbena-bonariensis-risk/

Why Grow Verbena?

Below are some of the main benefits of growing V. bonariensis in your garden:

Adds Colour

Many people want to add more colour to their garden and V. bonariensis are a great choice of plant to do this.

verbena flowers in a large. field with colourful butterfly sat on a flower

With its vibrant purple flowers, it will stand out even amongst other colourful plants. 

Attracts Butterflies

Verbena plants will also attract butterflies and other pollinators to your garden.

This is beneficial as they will help to pollinate your plants and beautify your garden.

Works Great With Other Plants
a country garden with an old potting shed and verbena bonariensis flowers and poppy seedheads in the foreground

Another great benefit is that it looks great when used with other plants, especially colourful perennials.

Mixing it with plants of other colours makes it very easy to brighten up your garden.

Planting

When growing Verbena, you can either buy plants that have already been established or grow them yourself from seed.

Let’s look at planting established plants first.

blooming flowers of Argentinian Vervain in a large park

Before planting, you should make sure you have a good spot for them.

They do best in full sunlight but can also tolerate partial shade, so bear this in mind when picking your spot.

When planting them, be sure to dig a generous-sized hole to accommodate the roots and it’s never a bad idea to use a good quality fertiliser after planting to encourage the best growth.  

the square shaped leaves of verbena bonariensis plant

If you’re growing from seed, then you have a couple of options – you can either plant them directly in the soil or grow them in containers first and plant them when they’re more established.

If you plant the seeds directly, then the best time to do this would be in April/May.

This will give them plenty of time to become established and they’ll benefit from direct exposure to the sun during the hottest period of the year.

butterfly sat atop the flowers of purple top

If you want to grow them indoors before planting, you should sow them around three months before you plan to plant them.

The benefit to growing indoors is that you can grow your plants earlier, since they’ll be protected from frost during the winter.

When To Plant

The best time to plant (when planting directly in the soil) would be in early spring.

Verbena bonariensis growing in the wild with wind turbines in the background

As mentioned above, you can grow them earlier than this if you have them in containers.

Plant Care & Growing Tips

Watering

How often you need to water your plants will vary depending on the season.

Spring would be the best time to plant V. bonariensis and during the hotter periods in spring/summer, you should water them around once per week, taking care not to cause the soil to become waterlogged.

a field of purple vervain flowers being watered by a large sprinkler

Make sure to soak your plants well but don’t let them sit in oversaturated soil for too long since it can cause the roots to rot.

To avoid this, you should water them on sunny days and water as early in the day as possible so there’s plenty of time for the sun to evaporate any water.

Maintenance

It’s a good idea to add a layer of mulch to your plants in the autumn.

This will help to protect the roots during any frosty periods in the winter.

Pruning
shrubby Verbena bonariensis in a herbaceous border

Although these plants don’t require too much pruning, it can help to encourage new growth, so it’s not a bad idea to lightly prune them as you see fit.

The best time to prune your plants is in early spring – usually around March – this will ensure that new growth comes through and your plants will be looking their best for the summer.

Habitat & Growing Conditions

V. bonariensis is native to South America and can be found in many countries throughout the region, including Brazil and Argentina.

a stunning multi-coloured butterly sat on Verbena bonariensis plant
Butterflies love Verbena, so they’re a great choice if you want to attract them to your garden

They enjoy a sunny climate, although they can still survive in colder climates, particularly as they self-seed so well.

Propagation

Propagating often isn’t necessary because these types of plants self-seed naturally – however you can propagate them yourself very easily using cuttings in containers.

dry seed heads of vervain in winter

The best type of stems to use would be those that look healthy but don’t have any flowers or buds. Then, follow these instructions:

  1. Prepare a container by packing it with some good quality soil and then plant the cutting into it.
  2. You should make a hole that’s roughly 2/3 the size of the cutting when planting. Be sure to water it well immediately after planting.  
  3. Although V. bonariensis generally enjoy the heat, it’s important that you don’t leave any cuttings in direct sunlight. Instead, you should find a partially shaded area and ideally use a propagation mat, so you can control the temperature.
  4. You should regularly check on your cuttings to make sure they’re thriving. You should only water them when the soil feels dry and it’s better to use a spray bottle rather than pouring water into it, since it’s very easy for the soil to become overly saturated.
  5. After 3-4 weeks, your cuttings should have taken root. To check if this is the case, you should gently pull them at the base. If you feel resistance, then they have taken root.
  6. You should wait another month or two before planting them outside. Be sure to pick a good spot, with plenty of space that gets at least some direct sunlight during the day.

“If taking cuttings of Verbena boniarensis, I will do it in September and peel away side shoots from the main stem, which root easily,” shares Colin Skelly, a Horticultural Consultant.

“I rarely do this, though, because they self-seed so readily and I harvest seedlings from the garden if I need them.”

Common Diseases & Problems

In general, V. bonariensis is resistant to diseases and pests, but there are certain problems it can suffer from:

Powdery Mildew

Powdery mildew is a common type of fungus that affects many plants.

It gets its name from the fact that infected plants develop a layer of mould on their leaves that resembles powder.

If you notice any plants that are affected by powdery mildew, you should remove and destroy them, since it can spread very easily.

magnified view of powdery mildew on the leaf of a plant

Powdery mildew thrives in moist conditions – knowing this will help you to take steps to prevent it from appearing in the first place.

Firstly, you should make sure that there’s plenty of space between each plant. This will help to improve circulation.

You should also take care when watering your plants to ensure you don’t get any water on the leaves. This is very often why powdery mildew develops.

It’s also a good idea to water your plants earlier in the day, so there is plenty of time for them to dry out in the sun.

Leaf Spot

Leaf spot manifests by causing the leaves of infected plants to develop small red/brown spots.

Not only does it look unsightly, but it also affects a plant’s ability to photosynthesize properly.

If you notice any plants that are affected by leaf spot, then you should immediately dig them up and destroy them.

As for avoiding leaf spot, the same advice for powdery mildew applies.

You can treat less severely infected leaves with a fungal spray too.

Rust

Rust gets its name from the fact that infected leaves develop reddish/brown spots.

If you catch it early, then it’s usually not too much of a problem and you can simply pick off any leaves that are affected.

You can also use a fungicide to treat rust.

However, if it’s more widespread, then it’s usually better to get rid of the plant to prevent it from spreading to others.

Spider Mites

Pests usually aren’t a problem for Verbena, but spider mites can sometimes be an issue.

close up of spider mites on a plant

Not only do they pierce the leaves of plants, but female mites can lay many eggs, which hatch very quickly.

If you notice spider mites on your plants, then you should spray them with water or use a good insecticide. 

Aphids

Aphids can also be a problem for V. bonariensis, although they’re quite easy to get rid of.

ladybird shown feeding on aphids on a verbena plant

You can simply spray them with water to remove them from the leaves of your plants.

It’s also a good idea to encourage insects that feed on them to inhabit your garden, such as ladybirds.

Scale

Scale infestation causes problems for plants for a couple of reasons.

Firstly, it will make it difficult for affected plants to photosynthesize and therefore affect their growth.

magnified view of black scale shown on the leaf of a plant

It can also cause plants to lose their leaves when it’s more serious.

Using insecticidal soap can help to keep plants free of scale, but treatments may need to be done regularly to ensure you kill off any remaining eggs.

FAQs

Should I Pinch Out Verbena?

Pinching out V. bonariensis when they’re young will encourage them to branch and give them a more pleasing appearance, so you certainly shouldn’t be afraid to do this when you think it’s needed.

How Far Apart Should I Plant Them?
bright lilac coloured flowers of Verbena bonariensis in a large perennial field

It’s a good idea to leave approximately 10 inches between each plant.

This will ensure they each get enough moisture when you water them, and that air circulation is good too.

Are Verbena bonariensis Plants Perennial?

Yes. Once you’ve planted Verbena, you can expect them to last for several years, providing they’re properly cared for.

What Are The Best Soil Conditions?
gardener shown planting verbena in soil

These plants do well in soil that’s moist and well-drained.

They can also do well in chalky and clay soils.

Using fertiliser and mulch in the autumn/winter can also help to make the soil conditions better and ensure they’ll thrive.

Is It Better To Buy Plants Or Grow From Seeds?

The obvious benefit of buying plants that are established is that you can get the benefit of them immediately and can add colour and interest to your garden without having to wait for them to grow.

magnified view of the seed head of a Verbena plant

Providing you get them from a quality supplier, you also know that they will be healthy and have been grown in optimal conditions.

Growing from seed has its own advantages too though.

When growing from seed, you can control the type of soil and fertiliser used as well as how often they’re watered.

There’s also a satisfaction that comes with watching your flowers thrive over the weeks and months.

References

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