You put tennis balls bird bath water to slow down ice formation during cold weather. The balls float on the surface and move with the wind. This movement disrupts the water just enough to prevent bird bath ice from forming a solid sheet across your basin. Birds need liquid water year-round, and this simple trick helps keep a small patch of your bath open during light frosts.
I tried this bird bath winter hack during a cold snap last January when temperatures dropped to 30°F (-1°C) overnight. I tossed two old tennis balls into my stone basin before bed. By morning, the edges of the bath had a thin ice layer, but the water around each ball stayed liquid. The balls had drifted overnight with the breeze and kept two fist-sized patches of open water available. A chickadee was already drinking from one of those open spots when I looked out my kitchen window at sunrise.
The physics behind this trick are straightforward. Wind catches the lightweight tennis ball and pushes it across the water surface. Even a gentle breeze creates enough movement to disrupt ice crystal formation. Water needs to be still to freeze into a solid sheet. The ball's constant drifting keeps breaking up those early ice crystals before they can connect and lock the surface down. You get the same effect you'd see in a stream where moving water stays liquid long after still puddles freeze over.
This method works best during light frosts between 28°F and 32°F (-2°C to 0°C). Your tennis ball bird bath freezing trick works well at these mild temps. Once temperatures drop below 20°F (-7°C) for more than a few hours, the balls can't do much for you. The cold overpowers the small amount of movement they create, and your bath will freeze around them. You'll find the tennis balls stuck in solid ice by morning during a hard freeze.
If you live in a region with extended freezing winters, you need more than tennis balls to keep your birds watered. A proper bird bath heater costs between $20 and $40 and uses a thermostat to keep water just above freezing all winter long. De-icers that float in your basin use electric heating elements instead of water movement. These tools prevent bird bath ice from forming even during the coldest nights of the year. Tennis balls make a nice free supplement to a heater, but they can't replace one in serious cold.
You can also try other bird bath winter hack methods alongside your tennis balls. A dark-colored basin absorbs more heat from the sun and melts thin ice faster during the day. Placing your bath in a sheltered spot near a south-facing wall helps it catch maximum sunlight. Some people add a ping pong ball for extra movement, though tennis balls work better because they're heavier and catch more wind.
Tennis balls are the cheapest and easiest way to help your birds during mild cold snaps. Grab a couple from your closet or the dollar store and toss them in your bath before the first frost hits. Your birds will thank you for that small patch of open water when everything else in the yard has frozen over. Just don't rely on this trick alone if you get weeks of sub-freezing temperatures where you live.
Read the full article: Bird Bath Guide for Your Garden
