A Safe, Simple Way to Prepare your Backyard Pond, Koi and Goldfish for Winter

A well-planted, backyard water garden filled with fish is quite spectacular in the Summer. There’s nothing quite as therapeutic as getting lost in the sights and sounds of falling water, while Koi swim lazily between the Lily pads to greet you at the water’s edge … that is, until Fall arrives. Then it’s time to Winterize the pond and put your fish to bed for the Winter. And since they’re going to spend the entire Winter outside, it’s important to prepare Koi (Japanese for Carp) and Goldfish properly to ensure they wake up happy and healthy in Spring. Here’s the approach I use to close my pond every Fall. It’s an approach I’ve adapted from others who’ve written about their experiences, and so far, I haven’t lost a single fish yet.

Note: My pond is 8′ x 8′ x 2′ deep (with straight walls), in Zone 6 where temperatures can reach -10F (-23C) in Winter.

Fish Requirements in Fall-Winter

Koi and Goldfish are hearty species that can tolerate cold temperatures outside. In Fall, when the water temperature drops below 45F, fish will slow down, stop eating and become inactive. But while they appear to be ‘sleeping’ on the bottom of the pond, they are still nonetheless ‘breathing’ the oxygen in the water. In this state of hibernation, they don’t use much energy but it is critical that they don’t run out of oxygen. Problems occur when a pond freezes over in Winter and there is insufficient oxygen in the water to sustain the fish throughout the Winter months. For this reason, I run a pump and an aerator stone all Winter long to continuously replenish the oxygen supply in the water. I also use a pond deicer (ie., a small heater, in the shape of a life saver), which floats above the aerator and keeps a small spot on the pond’s surface free from ice (so oxygen can get in and toxic gasses can get out).

Pond Covering for Fall-Winter

Just before the trees drop their leaves, I remove all annual pond plants, cut back perennials, vacuum the pond bottom and cover the pond to keep new leaves out (leaves and other debris in the pond use oxygen and release toxic gasses as they decompose). To cover the pond, I use 2″ x 2″s with a fine-mesh net stapled to the wood. I purchased the net from a local garden-pond store; the mesh is fine enough that even a pine needle can’t slip through it. Lastly, I cover the wood-net frame loosely with a plastic sheet (basically, an industrial-strength, painter’s drop sheet) and wait for the snow. Snow that falls on the plastic has an insulating effect, like a blanket. And on sunny days, the sun melts the snow and penetrates the plastic to create a greenhouse effect below. As a result, the pond’s entire surface appears to stay ice-free all Winter long … perhaps suggesting that a pond deicer is not essential with this particular setup. Experiment for yourself and see what works best for you. Then rest well this Winter, knowing your fish are doing the same.

Related Articles

Koi Fish Meaning, koi-pond-guide.com
Goldfish for Ponds, PondExperts.ca
Creating Water Gardens, Ortho, Meredith Books
The Pond Doctor, Helen Nash, Sterling Publishing
The Living Pond, Helen Nash, Sterling Publishing


5 thoughts on “A Safe, Simple Way to Prepare your Backyard Pond, Koi and Goldfish for Winter

  1. Pingback: The Koi Story- A Tribute To My Dad | this man's journey

    • Hi Anna. You’re right. I am indeed an animal lover and a big fan of Koi. And there’s definitely a lot to sort out if you’re planning on keeping Koi in a backyard pond. In Canada, adding aeration is critical in winter if your pond isn’t that deep. This past winter, I used the set up I described above in my post but didn’t turn the de-icer on – just used the airator stone and pump by itself. Worked like a charm. No issues. One less thing to worry about next year.

      cheers, your blog looks great,

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