Invasive plants! Avoid these for garden harmony!

So many pretty plants. But do you want them in your garden? Some, certainly. Others, definitely not. Plants have many different appealing features and many of these are highly desirable. Beautiful bling on the foliage front, perhaps. Scent to drool over. Flowers that flaunt themselves. Great structure. But there’s more to some plants than initially meets the eye. Let's look at some of the more common culprits. We all know about Japanese knotweed (Fallopia japonica), for example. It originated in Japan and was brought to Europe around 1829 as it was deemed to be a nice ornamental plant. ‍

Japanese knotweed! It can strike fear into the hearts of gardeners and house-hunters alike as this is an invasive plant that has to be declared on the searches. All Japanese knotweed is a clone of the original female plant. We now know that any part of the plant can grow into a new plant. Even the tiniest snippet. And we know that it grows at an alarming rate and can break through paths, walls and even houses. ‍ 

Here it comes! Japanese knotweed is a beast! Not all plants strike fear into the hearts of all who happen to have them in the garden. But there are many unwanted visitors that come in unexpectedly. Three-cornered garlic, for example. Allium triquetrum looks a bit like a bluebell until it flowers. Then the drooping white flowers give the game away. Those who look more closely will notice the stems have three angles, hence the name.   ‍

Three cornered garlic, otherwise known as three cornered leek This invasive, non-native plant spreads like wildfire. It crowds out spring flowers such as primroses and violets and can easily colonise roadside verges and banks. It is now common in the south east and western UK and is deemed to pose a critical risk, being listed on Schedule 9 of the Wildlife and Countryside Act. The invasive Rhododendron ponticum is also a well-known culprit. ‍

Rhododendron ponticum is a familiar sight in the countryside. It's taking over and crowding out the native plants. It is tall and evergreen with showy pinky-mauve flowers. Planted back in the Victorian era, it now dominates many areas of the UK where it crowds out other species. There's also the giant hogweed, Heracleum mantegazzianum , which has sap that burns, Himalayan balsam (Impatiens glandulifera) and a whole host of water-loving plants also have been blacklisted. ‍

Giant Hogweed is a thug! It also has sap which burns the skin.   These all pose risks which are quite serious. But there are many other plants which are just an irritation. Take the chameleon plant, Houttuynia cordata. This looks perfectly gorgeous, with its red and yellow, variegated, heart-shaped small leaves. It smells wonderful too if you bruise the foliage. But you soon find that this little pest pops up all over the garden. If you decide to plant this you might be best to keep it in a pot or hanging basket. ‍

The sweet little Chameleon plant can soon become a weed-like pest that pops up uninvited all over the garden.   Creeping Jenny certainly lives up to its name too. Lysimachia nummularia has great foliage colour  it provides a splash of yellow groundcover. But once again, it just doesn't stop. You'll find it appearing all over the place and removing it feels a bit like pulling snagged pieces of wool from a piece of Velcro. ‍

Creeping Jenny just creeps too easily and it soon becomes a pesky weed.   Even periwinkle (Vinca minor and major) can both be annoying in their own separate ways. Vinca minor is a great plant for a shady place and will stop weeds colonising dark corners. But it won't know where to stop and will continue to spread. Vinca major has an untidy habit and its lax shoots will root wherever they touch the ground. It will end up drooping all over your borders like a lazy teenager who doesn't want to get out of bed. What about some of those hardy geraniums? On the face of it they are simply brilliant. And many of them are. But the pale pink Geranium macrorrhizum is a thug and if you leave it alone it will fill your borders and even encroach into the lawn. As with many of these plants, they are fine in moderation but you have to be prepared to halt their spread. Then there are blackberries, mint, the snowberry shrub (Symphoricarpos) and small trees that produce hundreds of suckers such as Rhus typhina (sumach). And many more, of course. ‍

Even some of the hardy geraniums (but not all) can be considered to be invasive.   Bamboos and Grasses Some bamboo can be invasive. But, when used skilfully it can add a great ornamental feature to a planting scheme. Sasa, for example, is a genus of bamboo species which can be rampant. This is a plant that creeps along just under the soil and can pop up several meters from the parent plant. So it's important to include a root barrier if you are planning to plant this and some of the other bamboos. Some ornamental grasses tend to self-seed. This can be a great bonus, but with grasses such as Anemanthele lessoniana they tend to move around the garden and don't necessarily stay where they are put. The same can be said for Carex pendula and Stipa arundinacea. So if certain ornamental grasses are vital for your perfectly planned planting scheme, choose with care. ‍

Anemanthele lessoniana is a beautiful grass but it tends to self-seed and will eventually move around the garden.