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The garden plants you want to avoid including Japanese knotweed, English ivy and giant hogweed

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With warmer weather and summer on the horizon now is the time that many of us take a look at our gardens and green spaces and work out how we can improve them for the nicer months of the year.

But some garden plants and trees can not only damage your property but might also risk devaluing it - targeting cracks in buildings and patios and growing through them.

Invasive plants can prove problematic for home owners, while those on the lookout for a new home should, say property experts, pay close attention to what's outside just as much as inside the home you might be keen to buy.

Japanese knotweed is among the plants people are advised to avoid
Japanese knotweed is among the plants people are advised to avoid

Property surveyor Bradley McKenzie from surveyors firm Stokemont talks through the plants and trees to be aware of and shares how difficult - and costly - they might be to tackle.

1. Japanese Knotweed

Removal difficulty : High

Japanese knotweed is an invasive plant with bamboo-like red shoots and shovel-shaped leaves.

Growing up to three metres tall in spring and summer, one of the worst qualities about this plant is that its roots can reach down 20 metres underground, which risks affecting pipework, foundations, patios and paving.

Due to the damage it can potentially cause the Japanese Knotweed is listed as a defect to the property by RICS Homebuyer Reports while more than 2,500 people search the internet each month for information about how to get rid of it.

Bradley explains: “We would highly recommend you seek professional help when removing them as they re-establish easily from even the smallest remains. If you prefer doing it yourself, pesticide would be the most effective method to kill those zombie-like plants.”

Ivy is easy to take down but can grow rapidly. Photo: Svitlana Tytska/ Shutterstock.
Ivy is easy to take down but can grow rapidly. Photo: Svitlana Tytska/ Shutterstock.

2. Ivy

Removal difficulty : Low

English or common ivy is both a super climber and great grower. Described by the RHS as a 'woody climber with dense fast growth', while it can provide great cover the horticultural society also recognises that its ability to grow quickly and self cling means it risks being a 'nuisance' and people may struggle to control it.

While it can be quick and easy to take down there is always a small risk that if left to grow untamed that it will seek out potential cracks in the wall, that then might damage the mortar or lead to dampness and even leaks.

English ivy can be removed with your hands by peeling it very carefully from the wall. It is also possible, suggests Bradley, to kill it at the root by cutting the ivy away and letting it all dry out and die off.

Hogweed can resemble cow parsley. Photo: Shutterstock (56710629)
Hogweed can resemble cow parsley. Photo: Shutterstock (56710629)

3. Giant Hogweed

Removal difficulty : High

Similar to Japanese knotweed, giant hogweed is also invasive with an ability to spread fast. Related to cow parsley, it can grow up to 10 feet in height, but it is one that most gardeners, says the RHS, will want to remove.

More easily spotted in June and July, the sap can cause severe skin burns, and because it is a tough task to remove it, it is not a species of plant homeowners would ever want to keep or encourage.

Stokemont's surveyors explain: "Widespread across the UK, especially around rivers and ponds, its sap is phototoxic and can cause severe skin burns or scars under sunlights.

"Though not causing direct harm to the property, buyers may still refuse to pay a higher price if present because of its high cost of removal - up to £15,000."

Trees are glorious in open spaces but those with them near property should seek advice, say surveyors. Photo: Shutterstock stock image.
Trees are glorious in open spaces but those with them near property should seek advice, say surveyors. Photo: Shutterstock stock image.

4. Poplar, Willow and Oak Trees

Removal difficulty : Medium

While most trees will cause no harm, large trees like Poplar, Willow and Oak can be more of a problem if they're left to grow too close to property because of the damage their extensive roots can cause. The roots on poplar trees, for example, are shallow and fast growing, can spread out to 40 metres and take up to 1,000 litres of water and nutrients from the soil.

If a tree is some distance from your house or other buildings it will most likely cause you no problems at all but those closer to drains, property and other essential structures should be watched more closely. It is worth remembering that all of these trees will naturally live for a very long time, so homeowners should consider that trees can be much harder to take out, if this ultimately needs doing, once roots are thicker.

The age of the tree, the soil type, its location and its proximity to other buildings should all be considered before deciding whether it might pose you a problem and you can and should always seek expert advice. Surveyor Bradley McKenzie cautions: "If grown too close to your property, they could lead to further risks of cracks in foundations, subsidence and other structural defects, potentially costing you £5,000-£25,000 to repair."

Himalayan Balsam in full pink bloom. Photo: Shutterstock.
Himalayan Balsam in full pink bloom. Photo: Shutterstock.

5. Himalayan Balsam

Removal difficulty : Low

Himalayan balsam is a relative of the busy Lizzie but this one can grow between two and three metres tall and is identified by its pink flowers seen in summer and early autumn.

The Royal Horticultural Society describes it as a 'major weed problem' that will not only invade riverbanks and wasteland but it also known to take over garden spaces too. The warning adds: "It grows rapidly and spreads quickly, smothering other vegetation as it goes."

The flowers of Himalayan balsam produce large amounts of nectar, says the RHS, and are therefore very attractive to numerous bee species but despite this the damage it can do to other plants is considerable as it steals all the light, nutrients and water from the ground. While not physically harmful to people the weed can have a significant ecological impact and so should be kept under control if you find it in your garden, if not eradicated all together, to ensure it doesn't spread to neighbouring properties or other land.

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