Is It Fine to Let Your Pond Freeze Over?
Once the temperatures drop below freezing, the surface of your outdoor pond will begin to get icy, slowly freezing over. Many pond owners worry about shutting down their ponds, wondering if letting the surface freeze over is okay. Whether or not you can let the surface water freeze depends on whether you have fish or other pond life and how deep the pond is. Deeper ponds with fish and other pond life can typically overwinter if they have a de-icer or aerator to help keep the pond oxygenated. Learn more about letting your pond freeze over and what pond products can be left outside for winter.
Fishless Ponds During Winter
If your pond has no fish, just plants, it's easier to let the surface freeze over without worry. You can prepare your pond plants, removing any that won't tolerate the freezing temperatures. Some plants need to be moved inside, while others need to be placed deeper into the pond. If your pond is shallow and will freeze all the way through, many plants will need to be relocated during winter.
Why Pond Depth Matters for Fish
Pond depth is super important when deciding whether to let your pond freeze over. During the winter, when the pond's surface freezes, the fish move to the bottom. The water at the deepest part of the pond is actually the warmest. They can stay here until the surface water thaws in the spring.
Fish are cold-blooded, which means they're less active during the winter. Their metabolisms need to be warmed up by their environment, so as the pond water gets colder, they become less active. During the coldest parts of the winter, the pond fish will seem asleep, barely moving and not needing to be fed. They do not need as much room as they would in the warmer months, but they shouldn't be overcrowded as it can lead to poor oxygenation and excess waste.
How Deep Does the Pond Need to Be?
A general rule of thumb is that a pond should be at least 24 inches deep to overwinter fish. If you have larger koi, they require more room (a 48 to 60-inch deep pond is ideal). Ponds with fewer and smaller fish often overwinter at 18 inches deep. The depth needed also depends on how extreme your winters can be. If you live in a warmer climate with less severe cold, your pond will have less freezing than in a northern area. Some ponds may have the first 12 inches of the surface frozen, while others can have just a few inches. If your pond isn't deep enough to overwinter your fish, you can move them inside in a temporary tank for the winter.
If you have a deep fish-filled pond, it's typically okay to overwinter your fish outside, but a section of the ice needs to stay thawed and open for the water to oxygenate. When the surface freezes completely, there is no way for the gases created during the pond's natural nitrogen cycle to release and for the water to oxygenate. It's essential to use an air diffuser and a de-icer (depending on how cold it will get) to keep some ice open to allow for aeration (never use force to open the ice!).
What Can Stay Outside
When the water temperatures drop to 40°F, it's time to remove your pond pumps and any water features. Running pumps and water features in the pond as the temperature drops can lead to overcooling, which is harmful to fish.
Water features can also be damaged as ice starts to form. Pond pumps and water feature pumps are meant to have water running through them at all times. Ice can block the tubing and lead the pump to run dry and overheat or burn out. Water left in tubing and pumps expands as it turns into ice; this can cause cracking. Carefully drain pond pumps, fountains, and any tubing and relocate to a warmer area for the duration of winter.
You can leave more aesthetic products like birdbaths and spitters (without the tubing) as long as no water is left in them. Lights (unless in the deepest part of the pond), floating foggers, and other pond accessories should be moved out of the pond and stored inside to prevent damage from ice.
Winter is an interesting time for pond owners, as many have to shut down their ponds and wait for the temperatures to warm back up in the springtime to resume water gardening again. Understanding what happens while your pond is shut down and what your fish are up to can help you figure out your winter plan. Whether or not shutting down your pond and letting it freeze over is a good option for your pond depends on a few factors, including pond depth, climate, and what type of pond life you have. Once you feel confident about shutting down your pond or relocating your fish, you can enjoy winter and relax!