Garden plants to avoid growing – from the destructive to the ‘poisonous’ and ‘lethal’

No matter how beautiful some plants may be, it’s important to always assess how safe they are for the pets and small children you live with. It may be surprising to a few, but certain varieties can cause hay fever, rashes, hives, and blisters. Some can deplete the water levels, crack the walls or even weaken your property’s foundation.

Jo Lambell, founder of Beards & Daisies and author of The Unkillables said: “It’s a great time of year for gardens, and plants should be popping up left, right, and centre.

“But be careful. While some plants may seem eye-catching, they can be invasive and poisonous.”

For a happy, healthy garden, gardeners need to find plants that give them the look they want and that are unlikely to cause problems.

Usually, popular annuals, perennials, and shrubs are known to trigger reactions more than other plants.

Whereas, pansies, African daisies, nasturtiums, alliums, and succulents are easy to grow and are safe plants to cultivate.

Here are the plants that are likely to be a cause for concern.

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Water hemlock

This plant typically grows in wet, marshy places and is often confused for its non-poisonous look alikes such as wild carrots or parsnips.

If accidentally ingested, the symptoms of poisoning are displayed by seizures, nausea, vomiting, abdominal pain, tremors, confusion, weakness, or dizziness.

Whitney Bromberg Hawkings, CEO, and co-founder of FLOWERBX said: “Some of the most dangerous plants are frustratingly among the most beautiful.

“Water Hemlock (Cicuta), which bears a close resemblance to Cow’s Parsley can be found dotted across the countryside the second the sun comes out, but can also be fatal to animals and humans alike within minutes of ingestion.

“It contains a highly poisonous chemical that is lethal if ingested, not to mention its strong carrot-like odor which makes it a garden foe.”

As an alternative consider water parsnip which looks similar to the Water Hemlock.

This herb with divided leaves and clusters of white flowers can be cultivated for its edible tuberous roots.

Japanese knotweed

Bradley MacKenzie of Stokemont explained: “Japanese knotweed is an invasive plant with bamboo-like red shoots and shovel-shaped leaves.

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“It can grow up to 10 feet tall in spring and summer. But the worst part about this plant is that its roots can reach down to 65 feet underground.

“The spread of Japanese knotweed underground could destroy pipework and drains and weaken building foundations or paving, leading to foundational collapse and poor flood defenses.”

The expert warned that it is important to check and take immediate and thorough eradication actions before it gets too late.

Woody Shrubs & trees or Houttuynia cordata are great alternatives to Japanese knotweed.

The latter is usually grown as a leaf vegetable, used for garnish.

If you like the idea of ​​growing your herbs, you could consider cultivating mint.

English ivy

English ivy is the most heard-about plant, and while it looks great in a garden, it can quickly become invasive and dangerous.

It can spread rapidly across the garden, killing off your other plants.

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It also can pose health risks, as it is somewhat poisonous, and can cause itchy skin or dermatitis.

Bradley said: “Commonly seen across Europe, English Ivy is dangerous to your house.

“With a strong wall-climbing ability, this garden invader could easily penetrate your wall cracks, damage the mortar, and bring dampness or leaks to the house.”

Since English ivy is essentially a creeper, gardeners could look at other creepers or vines to substitute, such as climbing hydrangea, trumpet creeper, Virginia creeper, or Passionflower vine.

For these creepers to truly shine, ensure you grow them on your garden fence for a decorative touch, or on outdoor walls.

Giant hogweed

The Giant Hogweed or Heracleum mantegazzianum can be biennial or perennial.

It produces white flowers held in umbels, all facing upwards. The flower heads can be as large as 60cm.

The plant contains high levels of furanocoumarins, a chemical that causes a burning sensation on the skin.

Jo advised: “Keep your eyes peeled for Giant Hogweed, an invasive species that resembles cow parsley and can grow up to 16 feet tall.

“Its sap can cause burns, so if you come across it, wear gloves and protect your skin when removing it.”

Annie and Jemma Charman, founders of Green Rooms, suggested: “A lovely substitute with similar lacy white flowers and tall billowing stems is Ammi Majus (False Bishop’s weed) or for an injection of limey yellow color with a similar starburst shaped flower head try Anethum graveolens.”


Annie and Jemma said: “Buxus, or Box, has long been a staple of the traditional garden, used for edging beds and pathways and clipped neatly into pleasing architectural shapes.

“However, in recent years, it has been plagued by the box caterpillar which will quickly ravage the plant, leaving it brown, covered in webbing, and unsalvageable.”

The way to find out if the plant is diseased, infected, or dying, is when leaves and shoots turn dark brown and start shrivelling and falling.

This can happen over several months or quite suddenly as well.

Instead, Annie and Jemma suggested: “Opt for Ilex crenata (Japanese Holly) or Pittosporum tenuifolium Golf Ball, both of which have small leaves and a dense growth like Box and can be neatly trimmed and shaped in the same way.”