Garden

Attention, gardeners: these plants are prohibited

Susanne Loacker

There really are some “forbidden” plants in Switzerland: rapidly reproducing neophytes (Greek for new plants) make life difficult for native species, trigger allergies or are toxic to humans and animals. Around ten percent of all neophytes in Switzerland are considered to be “problem plants”. Handling and selling them is therefore prohibited by law.

A giant hogweed plant is surrounded by bushes, grasses and a tree.
© Getty Images

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These are neophytes – and this is how you recognize them

The description “new plants” sounds harmless at first. And of course not every one of these plants is a threat. We are still grateful today for the fact that the potato found its way from the Andean region to Europe at the end of the 16th century.

However, efforts are made in Switzerland to combat highly invasive plants that reproduce rapidly and displace native species or that are toxic or highly allergenic. And this is exactly what the term “neophytes” is about.

Private properties are not yet monitored to check whether prohibited plants have been removed, but there are certainly people who demand such measures. In fact, new purchases and imports are prohibited, and corresponding border controls are carried out.

If you are unsure whether a specific plant on your property is one of the forbidden neophytes, the “PictureThis” app will help you identify plants on the basis of a photo. The app itself, which is available for Apple iOS and Android, is free of charge; the fees for in-app purchases range from two to 55 francs.

To find out which plants are not authorized in your garden, it’s best to consult Annex 2 of the Federal Release Ordinance. This includes a list of eleven plants that are not permitted according to the 2008 regulation. Four of these are aquatic plants:

  • Cockayne
  • Floating marshpennywort
  • Water primrose
  • Nuttall’s waterweed
Water primrose can be seen growing along a watercourse.

Water primrose is mainly spread by humans, for example by the illegal disposal of plants from garden ponds and aquariums in the wild.

Common ragweed / Roman ragweed

Their pollen and flower heads can cause severe allergies and asthma in humans. The annual weed, which is actually native to North America, spreads through displaced soil, but also through bird food. Although its occurrence in Switzerland has been documented since the First World War, its spread has only been invasive since the 1990s.

Roman ragweed likes hot summers – so it’s quite possible that it will prevail in Switzerland in the long term, despite all the resistance. In its early stages it looks similar to chamomile plants. If you have ragweed on your property, be sure to pull out the ragweed with its roots before mid-July (before flowering). And as a preventive measure, don’t feed birds ready-made birdseed in winter.

The picture shows a close-up of common ragweed.

Common ragweed (biologically Ambrosia artemisiifolia) can cause severe allergies and asthma in humans.

Giant hogweed

This umbelliferous plant, also known as giant cow parsnip, which grows up to three meters high, originally comes from the Caucasus. It forms substances which, in combination with sunlight (or a powerful lamp), cause painful blisters in humans and animals when touched. The blisters are a kind of burn and are difficult to heal. Giant hogweed was the poisonous plant of the year in 2008. If you plan to pull it out (early in spring), you should definitely wear protective clothing, including face protection. Start by mowing larger areas. The uprooted plants must be burned.

Close-up of a giant hogweed plant growing in a meadow.

Giant hogweed (Heracleum mantegazzianum) looks harmless but can cause painful blisters in humans.

Himalayan balsam

This delicate plant, which is actually quite beautiful, originally comes from the Indian subcontinent and was brought to Europe as an ornamental plant in the 19th century. It is also referred to as ornamental jewelweed. The plant has an immense system made up of innumerable fine roots.

The problem is that it grows up to two meters high extremely fast and displaces other plants at the same time. It is slightly toxic when fresh and is therefore used as an emetic in some cultures. The Bach flower “Impatiens” is made from Himalayan balsam.

In the fight against Himalayan balsam, you need patience above all else: the young plants have quite shallow roots and are easy to pull out. However, this has to be done over and over again and, above all, across the entire area, since the seeds from adult plants can spread over a distance of up to seven meters. This means that they multiply a great deal in width.

A close-up of Himalayan balsam – it looks like a delicate orchid.

Himalayan balsam (Impatiens glandulifera) is also called ornamental jewelweed.

Asian knotweed

There are three species of Asian knotweed, of which the Japanese knotweed is the most common. This plant, which is related to rhubarb, was grown in Europe for decades as a privacy screen and as food for wild animals.

It grows densely and quickly, displacing native plants in the process. Its strong roots, which can destroy buildings and embankment protections, are also problematic. Since the roots die in winter, the soil then erodes all the more.

Pulling out knotweed plants helps. If the infestation is severe, all the soil must be dug out and disposed of to a depth of about three meters, because the plant can regenerate from even the tiniest parts. The waste must then be incinerated.

Close-up of Asian knotweed. It resembles flowering elderberry.

Asian knotweed (Reynoutria sachalinensis) not only displaces native species, it also increases soil erosion.

Staghorn sumac

Sumac originates from eastern North America and came to Europe at the beginning of the 17th century as an ornamental plant. Its leaves turn a picturesque color in autumn and the tree is very easy to look after.

But that’s exactly why it easily becomes a nuisance. You shouldn’t grow it, but should remove it if possible, even if it looks beautiful, because it takes away the habitat of other plants. Although it has shallow roots, it can grow over a radius of up to five meters.

If you want to leave your staghorn sumac standing, have a root barrier placed all around it so that it does not spread uncontrollably. If you want to get rid of staghorn sumac, felling it is not sufficient: all the roots over a radius of five meters must be removed from the ground.

Staghorn sumac with fine leaves and dark red flowers.

Staghorn sumac (Rhus typhina) is a beautiful tree. You can leave it standing, but you must put a stop to the spread of its roots.

Narrow-leaved ragwort

This composite plant originates from South Africa and is invasive in many places around the world. It likes to grow on roadsides, and the yellow flowers are often seen along the highway. The spread of the plant, which is further encouraged by global warming, causes damage to biodiversity – by displacing native species – and it is also toxic. As it is quite resistant to all kinds of weed killers, there is no other option than to pull it out – as early in the year as possible before the ragwort starts to flower.

The yellow flowers of narrow-leaved ragwort.

The narrow-leaved ragwort defies all weed killers – and must be uprooted.

American goldenrod (including hybrids)

Since goldenrod, which originally comes from North America and Canada, forms persistent underground runners, up to 300 new plants can sprout on a single square meter in spring. For a long time it was used as an ornamental plant and as bee pasture.

Goldenrod is very invasive and robs other plants of light and nutrients due to its dense growth. You can check its spread by mowing close to the ground before flowering in May and then again in August. This weakens the plants. Smaller areas can be uprooted. The roots must be incinerated, not placed in green waste disposal.

American goldenrod with yolk-yellow flower umbels.

The American goldenrod (Solidago virgaurea) was used as an ornamental plant for a long time. However, it displaces other plants due to its rapid growth.

Other plants on the blacklist

If you want to do even more for biodiversity: in addition to the official Annex 2 of the Release Ordinance, Switzerland has a blacklist issued by the private foundation “Info Flora”, which currently comprises 41 plants. 16 others are on the watch list – which means that their distribution should be monitored.

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