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. 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. We’ll help you identify them by their looks (and aren’t they beautiful!), understanding in which invasive category they fall, where they are prevalent, and most importantly, why they are such problematic plants – and why it is best to get rid of them altogether.
Invasive Alien Plants (IAP) are classified as such because they are non-local and have been introduced and spread outside their natural distribution area. They pose many threats to our environment and indigenous flora, as well as fauna. If alien invasives take over an area, they will compete with and even completely replace native, indigenous flora. This in turn affects the food, shelter, nesting sites etc. of our fauna. IAPs tend to change soil nutrition as well as water availability, and can also affect the light coming through and an area’s temperature.
Our list covers Category 1 IAPs. By law, all plants in this category are prohibited and, whether in rural or urban areas, must be removed and destroyed.
We also provide a non-invasive alternative to each IAP listed, so there is no reason why your garden shouldn’t look its full glory.
This blog will cover:
- Ageratum conyzoides & houstonianum
- Kalanchoe delagoense
- Canna indica
- Echium vulgare
- Ipomea purpurea & Ipomea indica
- Lantana camara
- Lilium formosanum
- Mirabilis jalapa
- Nerium oleander
- Tradescantia zebrina
Ageratum conyzoides & houstonianum – Billygoat weed & Mexican (garden) ageratum
- Description: These annual herbs have bright green, soft, hairy leaves and produce fluffy attractive mauve, blue, pinkish or white flowers all year round. They grow about 30cm to max 1m high.
- Category & where prevalent: Category 1. Prevalent in Eastern Cape, Kwa-Zulu Natal Limpopo and Mpumalanga.
- Why is it a problem: People have introduced this plant as an ornamental into their gardens in the past as it is attractive, very hardy and tolerates many growing conditions. The fact that this plant flowers all year round is what causes a problem as this means that it is constantly producing seeds which is how this plant spreads. 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 there are hybridized forms of this plant available nowadays that have been bred to be sterile and not seed. Ageratum is said to be a good mosquito repellent when grown in the garden and is also said to have insecticidal and nematicidal (nematodes) properties.
- Non-invasive alternatives: Scabiosa ‘Butterfly blue’, Felicia ‘Glenwood’, Sterile Ageratums.
AKalanchoe (Bryophyllum) delagoense – Mother of millions/ Chandelier plant
- Description: This is a hard to resist alien invader. 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; it is indestructible. This madagascan perennial succulent has erect stems with pencil shaped leaves which 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 & where prevalent: Category 1. Prevalent 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, and that is that not only does it produce thousands of small plantlets at the tips of the leaves but it also produces small fruits with numerous seeds in it. This plant can quickly take over rocky outcrops, open forests as well as grassy remnant vegetation, competing with indigenous species. On top of this, the plant is also very poisonous to humans and animals.
- Non-invasive alternatives: Cotyledon flanaganii/orbiculata, Aloe cooperii, Senecio ficoides.
Canna indica – Indian Shot
- Description: This perennial rhizomatous plant exhibits erect, leafy shoots, with large green or purple-bronze leaves and 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 & where prevalent: Category 1. Kwa-Zulu Natal, Gauteng, Eastern Cape, Western Cape, Mpumalanga, Limpopo.
- Why is it a problem: This plant not only spreads via seeds but also has underground rhizomes, which means that it forms dense spreading clumps, competing with and often replacing indigenous species. The reason why people tend to want to have this plant growing in their garden is not only because it is an attractive ornamental, but also because it grows in very damp areas where other plants often struggle – it often invades swamps and wetlands. It sucks up so much water that it is actually said to deal with drainage problems.
- Other facts: The hard black seeds of this plant are often used for jewellery making as well as are 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. The leaves can be used to make paper. These facts are not being relayed to encourage keeping it in your garden. We are rather saying that when removing it, you can maybe make use of parts of the plant. Many non-invasive canna hybrids exist, which are actually a lot more ornamental.
- Non-invasive alternatives: Wachendorfia thyrsiflora, Zantedeschia aethiopica, Canna hybrids.
CannEchium vulgare – Blue Echium
- Description: Blue echium is a deep rooted biennial that can grow up to 1m. The leaves and stems are covered with coarse, white hairs. It has a very long flowering period with blue or purple flowers appearing from October through to April.
- Category & where prevalent: Category 1. Western Cape, Free State, Gauteng.
- Why is it a problem: This plant 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: The flowers of this plant, (related to borage) can be added to salads, crystallised or made into a cordial. The roots of this plant are often used 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 alternatives: Limonium perezii, Aristea ecklonii & capitata, Lobostemon fruticosus (not so easy to find but similar look).
Ipomoea purpurea & Ipomoea indica – Common morning glory & Perennial morning glory
- Description: These climbing and twining plants are highly attractive with 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 and indica is a perennial variety. In tropical parts, this climber can flower throughout the year but in other parts will flower from November-May.
- Category & where prevalent: Purpurea – category 3, indica – category 1 & 2 dependent on province. Kwa-Zulu Natal, Gauteng, Mpumalanga, Limpopo, Eastern Cape, 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 tends to invade 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 alternatives: Thunbergia grandiflora (not easy to find sometimes), Petrea volubilis, Wisteria sinensis.
Lantana camara – Tick berry
- Description: Tick berry is a spreading shrub or scrambler growing up to about 2m tall. The stems are covered with hairs and thorns and 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 and these colours are often all displayed in one head. Flowering takes place from September through to April and is followed by purplish-black fruits when ripened.
- Category & where prevalent: Category 1. Western Cape, Eastern Cape, Kwa-Zulu Natal, Mpumalanga, Limpopo, North West.
- Why is it a problem: The seeds of this plant are poisonous to humans and animals, particularly grazing animals. This plant is said to lead to massive livestock mortalities. Strangely enough, these seeds are not poisonous to birds and this is how the plant is dispersed so easily. It spreads so vigorously that it will replace indigenous plants and will lead to an area not being able to be grazed. The hairs and thorns on stems also lead to invaded areas almost being impenetrable.
- Other facts: The main reason this plant has become so invasive is due to humans planting them in their gardens and these plants being able to escape via seed dispersal. Supposed sterile flower varieties are cultivated but this cannot really be trusted as years ago there was a pure yellow form ‘brought out’, which was meant to be sterile, but this eventually became invasive as well. Lantana leaves are very medicinal and the stems have been used to make furniture.
- Non-invasive alternatives: Polygala fruticosa & Polygala myrtifolia, Orphium frutescens, Verbena hybrids (if you want lower growing).
LAKALANCHOE (BRYOPHYLLUM) DELAGOENSE – Lilium formosanum – Trumpet lily/ St Joseph’s Lily
- Description: The St Joseph’s lily is a bulbous plant that can reach a height of 2m high and has narrow, shiny foliage. From January through to March, magnificent, large, funnel-shaped white flowers are formed on spikes, which are highly fragrant.
- Category & where prevalent: Category 1. Eastern Cape, Kwa-Zulu Natal, Gauteng, Mpumalanga, 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 badly affect grasslands and wetlands.
- Other facts: An interesting fact is that the bulb is very much edible and can be cooked and eaten like a potato. It is very rich in starch.
- Non-invasive alternatives: Amaryllis belladona, Zantedeschia aethiopica, Non-invasive lily hybrids.
Mirabilis jalapa – Four o’ clock plant
- Description: The Four o’clock plant is a bushy perennial shrub that produces masses of fragrant, funnel-shaped, tubular flowers. The plant is named the four o’clock plant, because the flowers open in the late afternoon and then fade in the evening. These flowers come in pink, red, yellow, white and some bi-colours. The slight scent permeated 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 plant spreads easily via seed dispersal and thrives in conditions like dry sandy areas where other plants would struggle. It also flourishes if growing in summer rainfall areas. This plant has the capacity to completely take over and also doesn’t have many known pests and diseases.
- Other facts: This is a rather confusing plant as there are varying opinions as to how this plant can be used. Some people say it is edible to a certain extent and red dye can be made from the flowers, which can be used as food colouring, but others say it is poisonous. One confirmed use is that the red dye made from the flowers can be used for dying fabrics.
- Non-invasive alternatives: Azalea hybrids, Cistus species, Pentas lanceolata
Nerium oleander – Oleander
- Description: Oleander is an evergreen shrub or small tree with dark green hardy foliage and masses of beautiful pink, red or white flowers that have a strong, lovely fragrance, appearing from September. These flowers are followed by brown-red fruit follicles that split open to reveal seeds with tufts of hair.
- Category & where prevalent: Category 1. Eastern & Western Cape, Kwa-Zulu Natal, Mpumalanga.
- Why is it a problem: There is a massive misconception in regards to Oleanders, which is that 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 aliens because they spread rapidly via seed dispersal and land up competing with indigenous species.
- Other facts: Oleander, although it is one of the most toxic plants in the world, is used medicinally (but best leave this to the professionals who know how to work with it). Not only is Oleander poisonous when consumed, it will also highly irritate your skin if you come into contact with the milky sap, and when it burns it releases toxic fumes.
- Non-invasive alternatives: Non-invasive Oleanders, Bauhinia galpinii, Escallonia ‘pink’, Raphiolepis indica ‘Pink’.
Tradescantia zebrina – Wandering Jew
- 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. 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 plant was very popular as an ornamental because of its lovely colourful foliage but 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, competing and overtaking indigenous species. Secondly, the plant is known to cause skin irritations to humans as well as your much-loved pets.
- Other facts: The plant is said to have medicinal properties, but only to be used by those that know what they are doing.
- Non-invasive alternatives: Crassula multicava purple/red, Tradescantia virginiana hybrids, Ajuga reptans, Lamium maculatum.
No doubt, you would have recognised a number of these plants – you might even have them in your garden. They are all very attractive and are therefore hard to resist, but 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 IAPs pose when planted, propagated, traded or kept in our gardens.
The answer is simple: remove and destroy! And replace it with an environmentally friendly substitute. Should you need any extra information on how to remove and destroy these plants, then please let us know. Our maintenance team is also on standby to help restore your garden.