It is so easy to be taken in by plants recognised as desirable cultivated specimens that we willingly buy.
They can cause more headaches than common or garden weeds.
Sow or plant the following only once in your garden and you have their company for ever – Aquilegia (columbine), digitalis (foxglove), Chrysanthemum parthenium (feverfew), Arum italicum, Meconopsis cambrica (Welsh poppy), pot marjoram and borage.
The majority regenerate from seed that is either dispersed by a breeze, or more likely, bird activity.
We have them all in this garden, the most troublesome being arum, aquilegia and poppy, in that order.
Arum italicum Marmorata was bought for its marbled green and cream foliage, so striking in the border at present. Later, an upright spike of bright orange fruits will appear, and that’s when the trouble starts.
Blackbirds gorge on them, before dropping the single seed with a dollop of soil conditioner anywhere in the garden.
As it grows, a deep underground storage organ develops, giving it perennial status.
Hoeing is ineffective, you must remove every piece mechanically. But do wear gloves when handling this poisonous plant.
Oriental poppy is so irresistible. The huge papery blooms are relatively short-lived, but add such a wow factor to ornamental borders.
However, the perennial roots present a problem when you decide to move a plant to another part of the garden. They penetrate deep into the soil and tiny pieces left behind regenerate quickly on that spot.
Japanese anemones are popular perennials, ideal for cut flowers in pink and white.
They grow up to a metre tall, but if you decide to reposition a group, the trouble begins. Underground rhizomes are activated and invade anything planted on that spot in future.
Welsh poppy and columbine are prolific in establishing small colonies all over the garden, and looking attractive in the process.
Seedlings are easily dispatched with a swish of the hoe on a hot, dry day. However, these plants form tap roots, which once established are difficult to remove, especially when based at the heart of a favourite border perennial. They’re presently trying to colonise a lavender hedge on the east side of the house, and a group of chives on a vegetable bed to the west.
Admittedly, the combination of blue and yellow is striking, but this is typical of the way ornamental weeds attempt to win you over – you must be decisive and stop their marching.