Knotweed, bamboo, and blackberries: The pesky plants you need to dig up if you find them in your garden

For the gardeners among us, this can mean that weeds which grow from underground rhizomes are about to rear their ugly heads - any many of them require a little extra work to remove.

But it’s not just the lives of Japanese knotweed green-fingered Brits have to contend with in their lawns and allotments. Most of the plants now considered invasive in Britain were originally introduced as ornamentals, and similarly many popular decorative or useful plants will take over your garden if you let them.

Garden lovers also tend to be some of the biggest nature lovers, and with the Royal Horticultural Society (RHS) advising against using weedkillers to avoid inadvertently spreading poison throughout the food chain, for many of these more deep-rooted problem plants you’ll need to dig them out - before they run amok.

With that in mind, here are some of the weeds and other garden invaders you should be on the lookout for for this summer:

‘Destructive’ Japanese knotweed

Ah Japanese knotweed. It’s pretty white flowers hide a dark secret - the fact that the mere presence of this invasive plant on your property can devalue it.

Originally introduced as an ornamental plant, this knotweed has become such a big problem that homeowners now legally have to declare its presence when selling their property. This is because its bamboo-like stems are hidden deep underground but shoot up rapidly in the springtime. They can grow up to seven feet tall, with such aggression that they can even damage buildings and other structures.

However, it’s important to keep in mind is that if you do opt to remove knotweed yourself, you’ll need to take special care when you dispose of any cuttings or plant material. Due to it’s highly invasive nature, it’s actually illegal to throw it out with your regular garden waste - and doing so could land you a nasty fine. Unless you have the capacity to burn it, it might be better to get a professional in if you find knotweed on your property.

Bamboo and other aggressive weeds

Knotweed isn’t the only aggressive ‘weed’ you need to be on the lookout for. Bamboo, despite its elegant appearance and popularity in Eastern-style gardens, grows in a similar way with underground rhizomes, and can also quickly become invasive.

The RHS says that bamboo patches can quickly spread beyond their bounds, and shoots can pop up anywhere in the garden, or even through solid barriers - like your patio floor. Most weed-suppressing groundcover fabrics will not stop bamboo spreading either. If any rogue bamboo makes an appearance, perhaps from a neighbouring property, you’ll need to dig up the entire clump with a sharp spade, severing the rhizomes as you go - and pulling them out with a fork or trowel.

Horsetail is another deep-rooted weed that can spread quickly, although it forms carpets rather than clumps. Unfortunately, it’s poisonous to many animals, including dogs, so pet owners will want to be sure to get rid of it. Horsetail roots can grow up to two metres deep, and it can regrow itself from pieces of chopped root left in the ground - so hand-weeding is nearly impossible. If you spot these unassuming fronds popping up on your lawn, a full excavation is your best option if you want to make sure they are gone for good.

Similarly, bindweed - particularly hedge bindweed with its big, white trumpet-like flowers - also spreads underground. Its appearance is misleading, as it does most of its damage above ground, with its tendrils twining their way through other plants, smothering them. It’s hard to remove without damaging them, and it can regrow from its fleshy, 5m-deep roots it you don’t dig them out thoroughly.

Mint, blackberry, and other ‘thug plants’

The RHS also warns that several desirable garden plants can become “thugs”, taking over huge sections of your garden and pushing other plants out. Mint is perhaps one of the best know examples of this, but blackberry, raspberry, horseradish and Jerusalem artichokes are all edible plants that can end up quickly grow out of control.

Some decorative plants can cause a similar issue, including Japanese anemones, Chinese lantern plants, mind-your-own-business (sometimes called baby’s tears), comfrey and periwinkle. If you find them growing on your property uninvited, you’ll need to dig them up - being sure to pull up any rhizomes too.

It’s recommended that you grow these plants in pots to keep them manageable. If you already have them in the ground, you can also try destroying young plants with a hoe when they first pop up.

Deep-rooted dandelions and dock

Movements like No Mow May have helped drive many away from the over-manicured garden look, and have helped improved people’s tolerance for wildflowers and more diverse lawns. This is much to the benefit of wildlife that rely on these native plants, and as they bloom - so too does our biodiversity.

But while many gardeners might be more willing to accept that the oft-maligned dandelions and dock plants are friend rather than foe now, sometimes these and other deep-rooted natives can sneak their way into pavement cracks, and other places we wish they didn’t.

You can stop dandelions spreading to more sensitive areas by deadheading them, but to get rid of them permanently (again, please consider letting some stay for the bees!) you’ll need to dig out the taproot - the big, central root which runs the deepest.