November 13, 2026, 3:29 pm | Read time: 3 minutes
A simple garden trick often circulates online: placing a copper coin in a birdbath is said to reduce algae growth. The idea isn’t entirely unfounded, as there’s a chemical effect behind it. However, the trick is far from recommended, warns an expert.
Follow myHOMEBOOK on WhatsApp now
Why do some people put a copper coin in the birdbath?
A birdbath in the garden or on the balcony is an important water source for many native bird species–not just in summer. However, algae can form over time in standing water. To delay this, placing a copper coin in the water is suggested. This practice is recommended by garden expert Sam Stevens on the English news site Daily Express.
The idea behind it: Copper has an algae-inhibiting effect. The metal is considered a biocide–a substance that can inhibit the growth of microorganisms such as algae, bacteria, or fungi. Small amounts of copper ions can dissolve in the water, which are toxic to algae and slow their growth.
Also of interest: Setting up a birdbath–3 common mistakes
Does it really work?
Indeed, copper can, in certain concentrations:
- damage algae cell walls
- impair photosynthesis
- disrupt enzyme processes
This slows down algae growth. However, it cannot be completely prevented. Additionally, the 1-, 2-, and 5-cent coins commonly used in Germany are not pure copper coins but consist of an iron core with a copper coating.
Bird Bath on the Balcony – Guide and Tips
How Effective Are Toilet Fresheners Really?
Conservationist advises against copper coins in birdbaths
From a conservation perspective, the trick is not advisable. “We do not recommend placing copper coins in birdbaths,” says Silvia Teich, press spokesperson at NABU, in response to a myHOMEBOOK inquiry. “Cleanliness is very important for birdbaths to prevent the spread of diseases. Therefore, the baths must be cleaned daily with a brush and filled with fresh water.” This way, algae cannot form in the first place.
Teich also points out another issue. According to the expert, “Algae are certainly not the biggest problem with birdbaths.” Rather, it’s the germs that quickly multiply in standing water.
What really matters with birdbaths
Hygiene is crucial for the health of the animals:
- Change the water daily
- Thoroughly clean the bath with a brush
- Do not use chemical additives
- Use shallow, easy-to-clean containers
Even though copper generally has an algae-inhibiting effect, conservation experts advise against placing coins in birdbaths. The key is not a supposed trick but consistent cleaning and fresh water.