Behind garden walls and fences they lurk, and, in SAS-style operations, they hop over garden boundaries and virtually dig themselves in.
Alternatively, they strike in garden centres. The unsuspecting buyer is wheeling a trolley up and down the aisles. They turn their back for a moment, and in hops a laurel here and a choisya there. And, of course, when you get them home and planted they thrive - unlike many of the carefully chosen specimens you actually wanted.
The other way these plants make their almost miraculous appearances in gardens, is through landscapers and garden designers. It's a bit like that Milk Marketing Board advertisement - cheerful milkmen leading a line of walking bottles to the doorstep. From my own experience in the landscaper's van, I can tell you that these plants have virtually to be tied down, such is their exuberance at the prospect of being planted. Once in the ground their roots spread like wildfire. And even if they are not cared for they thrive, putting on new growth annually at a ferocious rate.
Some of these plants can, from time to time, pleasantly surprise even the most cynical plant snob. But in general, there needs to be a coup d'etat. The following plants can be safely banished.
Forsythia: it may herald the end of winter, but when you see one in every garden, its dazzling effects wear off.
Pampas grass (Cortaderia selloana): This can be a most elegant plant, but more often than not ends up badly used and battered. And have you ever tried to move it?
Common laurel (Prunus laurocerasus): it may do very well in shade but its large glossy green leaves make me want to run for cover.
Leyland cypress (Cupressocyparis leylandii) plus Cupressus macrocarpa and griselinia: These should be whipped out without any explanation. Mind you, perhaps a letter of condolence could be sent to the more choice members of their respective families.
Senecio greyi: when used well in an open sunny situation this can be a joy to behold. But more often than not it is lanky and woody and the flowers are sporadic.
Aucuba japonica 'Maculata': a perfectly fine plant, very useful for the shade - if someone didn't always come along and sprinkle it with lots of yellow paint.
Philadelphus: wonderful but totally overused. Vinca major or minor, who cares?
Clematis montana: gets out of control so fast. Wonderful when in flower, but more thought would lead to a better choice, like the 'President'.
Variegated poplar: a devastation to the land. This is the one plant that will singlehandedly stop an invasion by the Russians. It is deserving of its own scorched earth policy.
But, if we banish these popular favourites, what to replace them with?
Garden centres and nurseries are packed with other choices, some being old foot soldiers while others are fresh young imports.
Common gorse (Ulex europaeus) and yew (Taxus baccata) have been around for ever and may at first glance appear too ordinary. But both can give great service in the right setting.
Chinese gooseberry (Actinidia kolomikta) has splashes of cream and pink on its foliage as it matures. Another climber for colour effect is Hedera helix 'Buttercup', a variegated ivy which makes a change from 'Goldheart'. The leaves are a good deal smaller, slightly crinkled and have a lot more colour.
Arbutus unedo, the Killarney strawberry tree, is evergreen, hardy and produces its red fruit at this time of the year, while the false acacia (Robinia) should not be missed for leaf shape and colour.
In midwinter it is hard to beat witch hazel (Hamamelis mollis), with its heavily scented yellow flowers, so vivid against its bare wood.
And, lastly, an appeal to replant one of the countryside's finest plants: hawthorn is disappearing with the country's hedgerows. No tree offers such a refuge to our native wildlife.
Diarmuid Gavin is a writer and gardener, and runs the Dublin School of Garden DesignReuse content