Gardeners are being urged to leave a 1p coin in their birdbaths this week - in a bid to protect against a common winter problem.

Bird baths are one of the most popular additions to any . They provide a place for all sorts of birds, from robins to redwings, chaffinches, magpies, starlings and crows, to find a source of fresh water to drink and to clean themselves with.

Even in , sources of clean drinking water can be hard to come by, especially with many countryside areas being turned into housing estates and roads, leaving less and less natural habitat for our feathered friends to forage in.

But the growth of algae, the subtle green plant matter, can pose a risk to birds' health, infecting water with bacteria, which in turn can spread disease and harm birds.

That's why garden experts are urging people to place copper coins, such as 1p and 2p coins, in bird baths.

The coins slow down the growth of bacteria in the water thanks to the copper inhibiting bacterial growth.

Pre-1992 coins, with more copper content, work best, but newer coins can still have some effect. Before 1992, UK copper coins were 97% copper, whereas in 1992 it was changed to copper-plated steel. This is not to be confused with US advice - in the US, pennies reduced copper content in 1982, ten years earlier.

explains: "Algae in bird baths can occur from debris falling into the water, which is why it's important to refill them every couple of days. If you notice algae is persistently coming back, then give your bird bath a thorough cleaning and place a copper coin into the fresh water. This can help slow down the growth of algae."

House Digest explains the science: "The copper in the pennies releases ions, which slow the algae growth in water.

"While large quantities of copper can be harmful to birds, small amounts are safe, allowing you to use a few pennies in the bottom of your bird bath to keep the water clean and fresh.

"Since many birds, like crows and blue jays, are attracted to shiny objects, the pennies can also help you attract them to your yard and garden.

"For best results, replace the pennies every few months. The coins are an excellent alternative to harsh chemicals and cleaners which can be harmful to wildlife and the environment.

"While the copper pennies will help keep the water clean, it still helps to switch out the water whenever you water your garden or yard, particularly in warmer climates."