Rosebay: The beautiful and elegant wildflower which is actually a weed

And one of the biggest winners this year has been Chamaenerion angustifolium, once regarded as a thing of beauty, an elegant addition to any garden, but now considered nothing but a very successful weed.

As a wild flower, it is quite stunning, beloved by several forms of wildlife, and it was once regarded as a symbol of victory.

It was introduced from North America in the 18th and 19th centuries as a garden plant and it soon found that the British climate and terrain suited it admirably. So it escaped the confines of the garden and set about colonising the country, and its invasive behaviour has allowed it to become naturalised.

But the American Fireweed – our very own British Rosebay Willow Herb – became so successful at growing and spreading (it’s a perennial that increases its numbers by seeding and creeping with fleshy white rhizomes) that it was quickly turfed out of conventional beds and borders to discover a new life in the great outdoors.

In flower, it’s one of the most easily identifiable plants in the country. In large clumps, it makes a striking sight, and its fluffy seedheads fill the August air like large snowflakes.

It’s gorgeous; it’s also incredibly invasive and, to some people, a pest to be eradicated at all costs.

From June to August, the violet or rose-purple flowers open gradually; then those small seeds covered with white silky hairs are carried away on the slightest breeze; finally, the pointed leaves turn red and yellow in autumn before the top growth dies back.

Rosebay Willow Herb not only looks good but it also does some good - it is the main food-plant of the Elephant Hawk-moth caterpillar, its nectar is important for, and it was once used as food by native American Indians.

But if you hate it, you hate it, so cut it back, year on year, before it set sets seed – at least then you get to enjoy the flowers.

Convolvulus, aka bindweed, is also a winner and a loser - although it’s a beautiful, elegant flower, it possesses invasive tendencies.

It looks lovely when it’s creeping up an old fence or sprawling languidly over a patch of untended ground, but once it gets its roots into the garden, it becomes a menace. It may not have the thorns of a rampant bramble, but it can put up just as hard a fight.

And when the weather’s warm and the soil is moist, the likes of convolvulus and a host of other tough, tenacious weeds are having a field day.

Dealing with annual weeds as they pop through on patios, paving, paths and between flowers is not difficult. If you have the time and a strong back, just bend down and pull them out; if you don’t, then wet the weeds with a proprietary weedkiller and they should be dead – or dying – within a few days.

However, not all members of the convolvulus family are invasive. Groundcover varieties form low, trailing masses of round green leaves, bearing long funnel-shaped flowers. These forms are excellent for rock gardens or edging, particularly in hot sunny areas, and for tubs and mixed containers or baskets.

Meanwhile, although Eupatorium purpureum may go by the common name ‘Joe-Pye Weed’, it’s anything but a weed and much more of a prized, late-blooming perennial plant.

You may sometimes see it growing along roadsides where it can be an enthusiastic spreader, but it’s actually a member of the sunflower family and is a welcome addition to a wildflower or streamside garden.

It’s tall – normally well above six feet and sometimes nearer 10 – so it’s not the sort of plant for the front of a border, but newer varieties are far better behaved and more in keeping with what many people see as a plant for the modern garden.

So if you don’t have the room for, or just don’t want a statuesque version that blocks out he vie of next door’s, consider the dwarfs, some of which come with darker foliage and some of which boast white flowerheads instead of the more familiar mauve.

Dwarf varieties, such as Eupatorium purpureum ‘Little Joe’, grow to three feet in height while standard varieties can reach twice that height.

Joe-Pye Weed was named after a Native American herbalist, and was once used as a medicine to try to lower fevers; now, most gardeners use it to attract birds and butterflies and too appreciate its tall, stately grace at the end of the season when most flowers are past their best and are more concerned with dying back and preparing for winter.

Come autumn, the flowers fade and the seedheads form; give them a few weeks and they will be caught by the wind and drift off to create new colonies.

Propagation is best from softwood cuttings taken in late spring or by division in autumn as they go dormant, or in the spring just as shoots first appear. Any plant that appear, uninvited in the wrong place, can be pulled up and consigned to the compost heap.