Scientists at the British Royal Horticultural Society have recently most sensibly investigated which hedge plants are most effective at absorbing pollution from the soil and air; which climbers help cool buildings the most; and what seems best to plant to reduce the impact of floods from intense summer rainfalls.

Ivy wall won the 'cooling buildings' award. Hawthorn and privet worked best to reduce localised flooding. The anti-pollution hedging hero was easily won by the dense, hairy-leaved Cotoneaster franchetii, which they found was at least 20 per cent more effective at soaking up pollution compared with other shrubs. Cotoneaster was most effective in areas with heavy traffic, with little change in quieter streets.

This all sounds like wonderful news for Canberra. Cotoneaster, privet, hawthorn and ivy all grow brilliantly in our climate, tolerating drought, blazing summers, freezing winters and even a blizzard or two without shedding more than few leaves. Every one of them in an extremely vigorous grower.

Far, far too vigorous. Every one of them is also a major local weed. Luckily, they all have non-weed alternatives that are also far more beautiful, and not dangerous at all.

Ivy-clad walls look beautiful, for example - until the ivy begins to invade your roof space, cover your windows and destroy the mortar or cladding of your walls, and then stakes its claim as a ground cover for the entire surrounding area. While it's tempting to cover walls with a plant with aerial roots that will cling on without any additional support, those very roots are what destroys walls, fences and can be incredibly hard to remove once it spreads in the garden. Do not be tempted by miniature ivy, as I once was. It stayed miniature and obedient for about 15 years, then one branch suddenly turned large leafed and began to spread. Fast.

Star jasmine with its glossy green leaves and glorious white flowers is often suggested as an ivy alternative. I'd avoid anything that covers an entire wall, as it may harbour rat nests and other pests, and go for espalier fruit trees or camelias which give you about two or three metres of wall coverage.

Cotoneaster was once one of the most popular local hedging plants. It is now a distinctly unpopular weed, unwanted except by the berry eating birds who help spread its seedlings across the region. If you have cotoneaster, dig it out now - or at least clip off all berries until you have time to replace it with a fast growing hedge of bottlebrush, or a slightly slower growing hedge of sasanqua camelias, both of which will give you privacy and gorgeous blooms. They are also far more attractive generally, as cotoneaster's leaves and slightly twiggy appearance is, well, unremarkable, if not downright boring.

My favourite hedge just now is dwarf lilly pilly. Our dwarf lillypilly grew to about 1.5 metres and then neatly stopped, though it is almost always covered in flagrant pink new leaves. The bush did die back in the months when bushfires surrounded us and the garden was buffeted with gale force winds with oven breath. The poor thing also hadn't been watered all through the drought, either, and it's on shallow rocky soil over sand. Lillypillies are happiest in damp gullies.

I had planned to prune the dead branches right back, hoping the trunk would sprout again, but almost every branch has come back to life again, and it's once again a most delightful mound.

If you want a taller hedge, have a look at the lovely range of full-sized lilly pillies now available, as see which one you fall for. We grow more than 10 different lillypillies here, though sadly I can't tell you their names as most were grown from seeds I stuck in my pocket, and planted only when the pocket was about to go into the washing machine, by which time I could no longer tell which plant it came from, if I'd ever known.

If you are going to plant a hedge of them, choose with more discretion, and as with all hedges, make sure you plant all of the same variety, so your hedge grows evenly, and prune little and often to keep it bushy. Lillypillies are so vigorous they do need some attention, and yes, the birds will adore the fruit too - it is about 1000 times more ornamental than cotoneaster - and bees and many insects love the flowers. Lilly pilly root systems are usually not invasive, too, though it there is a crack in one of your pipes any plant roots are likely to head for the source of moisture.

Do water them when young, and to get them to grow high quickly if you want a screening hedge. After that they will just grow with infinite neglect. Even better - if your green thumb gets the better of you and other plants begin to crowd around them, lilly pillies do well in either full sun or dappled shade. One of ours is blooming and fruiting happily even after the canopy of a seedling avocado has covered it almost as effectively as an umbrella.

Admittedly lilly pillies may not soak up as much pollution as the hairy-leafed cotoneaster, but there is an easy cure for that. If good old hairy leaf soaks up 20 per cent more pollution, you can plant 20 per cent more lillypillies for the same effect, or better yet, twice as many, on the principle that the more beautiful plants around, the happier life is.

As for the hawthorn and privet, while I don't doubt their ability to hold the soil during sudden local floods, there are thousands of native plants which have been doing that job extremely well around here for many millennia. Plant, then plant some more.

Come to think of it, the Royal Horticultural Society may not even have tested lilly pillies, or bottlebrush, grevilleas, leptospermum or any Australian native plants at all.