Invasive Alien Plants – Beautiful, Harmful & Illegal

We're flipping the other side of the coin today to discuss 10 culprit plants and weeds that are often kept in gardens for their pleasing or extraordinary looks and ornamental value.

Today, we’re flipping the other side of the coin to discuss invasive alien plants. We will focus on 10 culprit plants and weeds that are often kept in gardens for their pleasing or extraordinary looks and ornamental value. But many gardeners do not understand the harmful impact of keeping these buggers in local gardens. These specimens are all on the invasive alien plant list of South Africa and pose a threat to our environment.

Firstly, we’ll help you identify them by their looks (and aren’t they beautiful!). Furthermore, this article will enable you to understand in which invasive category they fall, and where they are prevalent. Most importantly, we will discuss why they are such problematic plants – and why it is best to eliminate them altogether.

WHY ARE THEY CLASSIFIED AS INVASIVE ALIEN PLANTS?

Invasive Alien Plants (IAP) are classified because they are non-local. People have introduced these invasive plants in local gardens. Consequently, they now spread outside their natural distribution area. These invasive plants threaten our environment, indigenous flora, and fauna. If alien invasive plants take over an area, they will compete with and even completely replace native, indigenous flora.

This in turn affects our fauna’s food, shelter, nesting sites, etc. Invasive alien plants tend to change soil nutrition and water availability. Moreover, it affects the light reaching an area and the temperature. Our list covers Category one, Invasive Alien Plants. All plants in this category are prohibited by law.

To be part of the solution, you should remove and destroy all invasive plants found in rural or urban areas. We at Contours Landscapes, also provide non-invasive alternatives to each alien invasive plant listed. Consequently, should you remove all the illegal invasive plants and replace them with the plants we recommend, your garden will not lose any of its beauty.

What are some of the most common invasive alien plants in South Africa?

1. Billygoat weed & Mexican (garden) ageratum

Billygoat weed - one of sa's Invasive Alien Plants
Billy goat weed One of South Africas Invasive Alien Plants

Description: These annual herbs have bright green, soft, hairy leaves. They produce fluffy attractive mauve, blue, pinkish or white flowers all year round. These invasive plants grow about 30cm to max 1m high.

Category & area where prevalent: Category 1. Found in Eastern Cape, Kwa-Zulu Natal Limpopo and Mpumalanga.

Why is it a problem: People have introduced this plant into their gardens as an ornamental. Moreover, it is attractive, hardy, and tolerates many different growing conditions. The fact that this plant flowers all year round cause a problem. This means that it constantly produces seeds, enabling this invasive plant to spread. This plant is so vigorous that it has the potential to compete with and replace indigenous species. Also, all parts of these plants are poisonous to humans and pets.

Other facts: One needs to note that this plant’s hybridised forms are available nowadays. Thanks to agricultural science, hybrids are sterile and do not produce seeds. Ageratum is a good mosquito repellent when grown in the garden. Furthermore, it has insecticidal and nematicidal (nematodes) properties.

Non-invasive plant alternatives: Scabiosa ‘Butterfly blue’, Felicia ‘Glenwood’, Sterile Ageratums. 

2. Mother of millions/ Chandelier plant

Mother of millions - one of sa's Invasive Alien Plants
The Mother of Millions or chandelier plant is an Alien Invasive Plant

Description: This is a hard-to-resist invasive alien plant. It is indestructible not just because of its beauty but also because it is one of those plants that you do not have to have any form of green finger to grow. This Madagascan perennial succulent has erect stems with pencil-shaped leaves. They are pale green to brown with dark green to red spots. The deep orange to magenta cluster flowers are very attractive, resembling those of Cotyledons.

Category & area where prevalent: Category 1. Found in Gauteng, Kwa-Zulu Natal Limpopo and Mpumalanga. 

Why is it a problem: The problem is in the common name of this plant ‘mother of millions’. There is a double-whammy problem with this plant. It produces thousands of small plantlets at the tips of the leaves. Furthermore, it also produces small fruits with numerous seeds. This plant competes with indigenous species. It can quickly take over rocky outcrops, open forests, and grassy remnant vegetation. On top of this, this invasive plant is also very poisonous to humans and animals.

Non-invasive plant alternatives: Cotyledon flanaganii/orbiculata, Aloe cooperii, Senecio ficoides

3. Indian Shot (Canna LILY)

Indian shot - one of sa's Invasive Alien Plants
An invasive Alien Plant the Canna Lily is still found in many gardens

Description: This perennial rhizomatous plant exhibits erect, leafy shoots with large green or purple-bronze leaves. It produces red or orange tropical-looking flowers on top of tall flowering spikes. The green spiny fruits, when ripe, open up to release black, perfectly round, hard seeds.

Category & area where prevalent: Category 1. Found in Kwa-Zulu Natal, Gauteng, Eastern Cape, Western Cape, Mpumalanga, and Limpopo.

Why is it a problem: This plant not only spreads via seeds but also has underground rhizomes which form dense spreading clumps. The above-mentioned enables this invasive alien plant to compete with and often replace indigenous species. People tend to want to have this plant growing in their garden. It is an attractive ornamental, growing in damp areas where other plants often struggle. The Canna often invades swamps and wetlands. It sucks up so much water that it is actually said to deal with drainage problems.

Other facts: People often use the hard black seeds of this plant for jewellery making and for rattles in some musical instruments. It is also used to make purple dye. The rhizomes of this canna are edible when cooked and are even medicinal. You can even make paper from the leaves of this plant. We are not encouraging you to keep Canna Lillies in your garden by stating all these interesting facts. We say you can use their parts when removing the invasive Canna plants. Many non-invasive Canna hybrids exist, which are actually a lot more ornamental.

Non-invasive plant alternatives: Wachendorfia thyrsiflora, Zantedeschia aethiopica, and Canna hybrids.

4. Blue Echium (Blueweed)

Blue echium - one of sa's Invasive Alien Plants
The Blueweed plant is unfortunately categorised as an Invasive Alien Plant

Description: Blue echium is a deep-rooted biennial that can grow up to 1m. Coarse, white hairs cover the leaves and stems of this invasive alien plant. It has a very long flowering period with blue or purple flowers appearing from October through to April.

Category & where prevalent: Category 1. Found in Western Cape, Free State, and Gauteng.

Why is it a problem: This plants seeds and spreads very easily, invading cultivated crops, pastures, roadsides as well as home gardens where people try to keep it as ornamental. The plant is also poisonous and a skin irritant.

Other facts: People often add the flowers of this plant, to salads, crystallise it, or make it into a cordial. Furthermore, they often use the roots of this plant to make a red dye. When working with this plant, remember to wear gloves, as the hairs on this plant can hurt you and are a skin irritant.

Non-invasive plant alternatives: Limonium perezii, Aristea ecklonii & capitata, Lobostemon fruticosus (not so easy to find but similar look).

5. Common morning glory & Perennial morning glory

Common morning glory - one of sa's Invasive Alien Plants
The Morning Glory with its attractive funnel shaped flowers is an Invasive Alien plant

Description: These climbing and twining invasive alien plants are highly attractive. They have heart-shaped leaves and purple-blue, sometimes magenta to white funnel-shaped flowers. Purpurea is an annual form and, at some stage, will usually die back. Indica is a perennial variety. In tropical parts, this climber can flower throughout the year, but in other parts, it will flower from November-May.

Category & area where prevalent: Purpurea – category 3. Indica – category 1 & 2 dependent on province. Found in Kwa-Zulu Natal, Gauteng, Mpumalanga, Limpopo, Eastern Cape, and Western Cape. 

Why is it a problem: This plant spreads via the dispersal of very fine seeds and forms dense growth over other plants and trees, therefore competing with other species. It invades woodlands, riverbanks, coastal dunes, roadsides and home gardens. This climber is well sought after by people, which is what has also led to the distribution and invasion of this plant.

Non-invasive plant alternatives: Thunbergia Grandiflora (not easy to find sometimes), Petrea Volubilis, Wisteria Sinensis.

6. Tick berry

Tick berry - one of sa's Invasive Alien Plants
Dont let the colourful flowers of the Tick berry fool you Although beautiful this is an Invasive alien Plant

Description: Tick berry, also known as Lantana, is a spreading shrub or scrambler growing up to about 2m tall. Hairs and thorns cover the stems of this invasive plant. The leaves are dark green, rough, and have a strong smell when crushed. The flowers are pretty flat tops in pink, red, crimson, orange, yellow or white. The Lantana plant often displays all these flower colours in one head. From September through to April the plant flowers. Flowers are followed by purplish-black fruits when ripened.

Category & where prevalent: Category 1. Found in Western Cape, Eastern Cape, Kwa-Zulu Natal, Mpumalanga, Limpopo, and North West.

Why is it a problem: The seeds of this plant are poisonous to humans and animals, mainly grazing animals. This plant leads to massive livestock mortalities. Strangely enough, these seeds are not poisonous to birds, which is how the plant is easily dispersed. It spreads so vigorously that it will replace indigenous plants. Animals will no longer be able to graze once this invasive plant takes over an area. The hairs and thorns on stems also make invaded areas almost impenetrable.

Other facts: This plant has become so invasive mainly due to humans who plant them in their gardens. As soon as it produces seed, this plant can ‘escape’ via seed dispersal. Some people claim to have cultivated sterile flower varieties. Unfortunately, we cannot always trust these varieties. Years ago, a pure yellow form brought out was meant to be sterile, but it eventually became invasive. Lantana leaves are very medicinal. Some crafty people use the plant’s stems to make furniture.

Non-invasive plant alternatives: Polygala Fruticosa & Polygala Myrtifolia, Orphium Frutescens, Verbena hybrids (if you want lower growing).

7. Trumpet lily/ St Joseph’s Lily

Trumpet lily - one of sa's Invasive Alien Plants
The Saint Josephs lily with its magnificent flowers is unfortunately listed as an Invasive Alien Plant

Description: The St Joseph’s lily is a bulbous plant that can reach a height of 2m high and has narrow, shiny foliage. These invasive plants form magnificent, large, funnel-shaped white flowers on highly fragrant spikes. They usually flower from January through March.

Category & where prevalent: Category 1. Found in Eastern Cape, Kwa-Zulu Natal, Gauteng, Mpumalanga, and Limpopo.

Why is it a problem: This plant spreads via seeds and bulbs, which multiply. St Joseph’s lilies compete with and often completely replace indigenous species. They have a tendency to affect grasslands and wetlands badly.

Other facts: A fascinating fact is that the plant’s bulb is very much edible, and it can be cooked and eaten like a potato. It is very rich in starch.

Non-invasive plant alternatives: Amaryllis Belladona, Zantedeschia Aethiopica, Non-invasive lily hybrids.

8. Four o’clock plant

Four o’ clock plant invasive alien plants
The four oclock plant with its cute flowers is an Invasive Alien Plant

Description: The Four o’clock plant is a bushy perennial shrub that produces masses of fragrant, funnel-shaped, tubular flowers. The flowers on this plant open in the late afternoon and then fade in the evening. This is the reason why it is known as the four o’clock plant. These flowers come in pink, red, yellow, white and some bi-colours. The slight scent permeated by the flowers has a vanilla tone.

Category & where prevalent: Category 1. Gauteng, Limpopo, Mpumalanga and North West province. We have also noticed Western Cape and Natal gardens and areas with these plants overtaking.

Why is it a problem: This invasive plant spreads easily via seed dispersal. It thrives in conditions like dry sandy areas where other plants would struggle. It also flourishes growing in summer rainfall areas. This plant has the capacity to take over completely. Moreover, it doesn’t have many known pests and diseases.

Other facts: This is a rather confusing plant as people have varying opinions on what to use this plant for. Some people say it is edible to a certain extent and that they can make red dye from the flowers. Popular opinion is that one can use the dye for food colouring. On the other hand, some people say it is poisonous. One confirmed use is that you can use the red dye made from the flowers for dying fabrics.

Non-invasive plant alternatives: Azalea hybrids, Cistus species, Pentas lanceolata

9. Oleander

Oleander plant with flowers is an invasive alien plant
The Nerium shrub with its masses of beautiful flowers is an Invasive Alien Plant

Description: Oleander, also known as Nerium, is an evergreen shrub or small tree with dark green hardy foliage and masses of beautiful pink, red or white flowers. Appearing in September, the flowers have a strong, lovely fragrance. These flowers turn into brown-red fruit follicles that split open to reveal seeds with tufts of hair.

Category & area where prevalent: Category 1. Found in Eastern & Western Cape, Kwa-Zulu Natal, and Mpumalanga. 

Why is it a problem: There is a massive misconception regarding Oleanders. People think they are on the invasive list purely because all parts of the plant are highly toxic to humans, birds and other animals. This is not true. They have been declared alien invasive plants because they spread rapidly via seed dispersal and compete with indigenous species.

Other facts: Oleander is a medicinal plant, although one of the world’s most toxic plants. It is best to leave the plant’s medicinal use to the professionals who know how to work with it! Not only is Oleander poisonous when consumed, but it will also highly irritate your skin if you come into contact with the milky sap. Furthermore, when it burns, it releases toxic fumes.

Non-invasive plant alternatives: Non-invasive Oleanders, Bauhinia Galpinii, Escallonia ‘pink’, Rhaphiolepis indica ‘Pink’.

10. Wandering Jew

Invasive alien plants in south africa - the wandering jew
The Wandering Jew with its attractive foliage is an Invasive Alien Plant

Description: This perennial, evergreen creeper grows to about 500mm high and has attractive bluish-green foliage with two broad silver bands above and purple below. The Wandering Jew flowers on and off through the year with pink or violet-blue, small, pretty flowers.

Category & where prevalent: Category 1. Particularly bad in Eastern Cape but can become problematic anywhere.

Why is it a problem: This invasive plant was very popular as an ornamental because of its lovely colourful foliage. However, there are a couple of reasons one should not plant it, or let it exist in your garden. Firstly, it spreads like crazy via fragmented stems and roots, as well as seed dispersal. It will invade and take over shady spots, disturbed forests and stream banks. Furthermore, it will compete with and overtake indigenous species. Secondly, the plant causes skin irritations to humans and our much-loved pets.

Other facts: The plant has medicinal properties, but is only to be used by those that know what they are doing.

Non-invasive plant alternatives: Crassula multicava purple/red, Tradescantia virginiana hybrids, Ajuga reptans, Lamium maculatum.

I have invasive alien plants in my garden. What Now?

You would have undoubtedly recognised several of these invasive alien plants – you might even have them in your garden. They are all very attractive and are, therefore, hard to resist. At the end of the day, the most important thing is that we protect our environment and local flora and fauna. This means not contributing to the persisting problems that these invasive alien plants pose when planted, propagated, traded or kept in our gardens.

THE ONLY SOLUTION TO GET RID OF INVASIVE ALIEN PLANTS – REMOVE AND DESTROY THEM!

The answer is simple: remove and destroy! And replace it with an environmentally friendly substitute. Please let us know if you need any extra information on removing and destroying these invasive alien plants. Our Garden Maintenance team is also on standby to help restore your garden.

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Let’s plan your landscaping project together!

We plan, install and maintain award-winning landscapes for our commercial clients and project partners. Clients who wish to add function, value and inspiration to their outdoor spaces and properties.

Our roots are in Cape Town, but our footprint stretches deep into southern Africa.