winterizing the water garden: top tips

IN MORE THAN 20 YEARS of operating two homemade in-ground water gardens, I have probably broken lots of rules—especially about winterizing. But there are some rules I never break, and keeping the surfaces from freezing over is the most important one of all.

If trapped under a solid sheet of ice, decomposing plant material and wastes from fish or other inhabitants can create a building of noxious elements such as ammonia, nitrites and carbon dioxide, all of which can harm (or suffocate) any life overwintering in the pool, and also taint the water.

Make a plan now to keep a hole in the ice; never let the pool freeze completely over. Depending on the pool size and your wintertime lows, maintain at least a small hole in the ice with an appropriate wattage level of floating pond de-icer (that’s one of mine, above; there are many styles and sizes). Water-garden suppliers can help you choose the correct de-icer.

Some water gardeners use a bubbler, or aerator, operated by a pump and submerged maybe 6 inches and positioned near the edge of the pool, to keep a hole open; that doesn’t work here in a harsh winter, but may for you. In early spring, before I pull the de-icer, the frogs act as if it’s a float to sunbathe on (below). All winter long, the birds thank me for supplying water as a side-effect of my de-icing scheme.

I am in a cold-winter zone, so I turn off my pumps around Thanksgiving, meaning the spillways and biological filters are no longer operational.  I don’t pull my pumps (some experts recommend it), but what turning off the water does is protect tubing–much of it is exterior to the pool–from freezing, then perhaps rupturing during thaws. I do lift, empty and clean external filters (because they, too, would freeze and crack).

I don’t drain or clean my pools in fall or spring specifically, however, or actually anytime, but work all season long to maintain a healthy water condition instead—going on that “an ounce of prevention” mantra.

Most helpful tools on that score: plenty of submerged oxygenator plants such as perennial parrot feather (Myriophyllum) and anacharis (Elodea), and also floating ones that shade the surface (helping limit algae growth). The parrot feather (seen, above, just starting to poke through the surface in late spring), which is perennial in my small pools even here in Zone 5, does some shading once it starts to fill in. I also love the dainty little true floaters such as Azolla and Lemna (covering the pool in the above photo). Note: Never put any aquatic plant into natural waterways; they are only for use in lined water gardens and pots.

In fall I trim any that are up and over the edge, and thin somewhat if the pool seems congested. (Non-hardy plants must be removed before frost, and stored or discarded.)

Using a net or skimmer, I also remove leaves that blow in regularly, especially in fall, and use biological (non-chemical) additives spring and summer to stimulate the decomposition of pond debris. These are helpful bacteria, specifically. Note: I don’t strive for the bottoms of the pools to be muck-free, however; my amphibian friends love a nice cushion of glop down there to sleep on, or in.  Though my pools are just 1,800 and 800 gallons, several frog species and two salamander species reproduce in them year after year. Amazing, and a wonder I never tire of celebrating.

And if you have seasonal water gardens in pots—remember mine, above, by the kitchen door?—be sure to empty and store them if the container’s not weatherproof.  But you probably already figured that part out.

got fish? stop feeding

ONCE THE WATER is below about 50 degrees, I don’t feed the comets (very hardy goldfish-like creatures) who have lived for many years in one pool.  They do fine without supplemental food pellets until spring. My fish actually tell me around October that they are done eating; even if I toss pellets into the pool, they show disinterest once it’s cold.

November 12, 2012


  1. Maddybee says

    Thanks for this. When our water garden was installed about 6 years ago the designer told us to keep the pumps going all winter (there are 2 water falls) to prefent freezing and that is what we’ve done. As a result our pond never fully freezes and the hibernating frogs come back yearly. We have considered a floating de-icer instead of running the pump all winter and maybe we’ll try it this year now that I’ve read your post.

  2. Meredith says

    What a great idea! I’ve been in a dither trying to figure out how to keep two trash cans full of rain water that I saved for house plants from freezing. The top of each had a layer of ice this morning. I was just despairing over how much colder it was supposed to get tonight when I saw your tip. I dug out two small fountain bubblers and have them running now but it won’t be long before they won’t be able to keep up. I’ll check the local farm store for a couple of those floating de-icers tomorrow. Thank you so much for the tip!

    • says

      Hi, Meredith. There are even small de-icers (small enough for a birdbath, for instance) so I Know you’ll find the right thing — most of the water-garden places are so helpful on the phone, so don’t hesitate to call and ask.

  3. Burndett Andres says

    Margaret – Thanks for reminding me to order a birdbath heater. I’ve been meaning to do it for some time. Thanks also for sending the copy of “A Way To Garden.” It’s a Wonderful Treat – great reading and very informative. Can’t wait to read your new book. XOXO

  4. Becky says

    Here in the central mountains of West Virginia we have a great grey heron visiting our pond. He has cleaned out the small comets and is returning daily. Hoping to have a feast of our large koi. We have 4 that are over a foot long. Last year he was able to take number 5. I always thought of heron as being found at coastal regions. I guess maybe they have widened their territory. We are laying some large plastic black pipe in the pond tonight hoping the koi will hide from Big Bird in that. We have a river nearby but our pond is easier fishing I suppose.

  5. says

    What lovely pools. I only have a concrete birdbath/fountain. I just brought in the pump and covered with a tarp, and the next day we had the first dusting of snow!

  6. Dahlink says

    Margaret, thanks for all these reminders. We have pretty much followed all your recommendations and feel ready for winter. One thing we go back and forth on is the wisdom of putting a net over the pond in the fall. We did this the first few years, and I know we thwarted a fish-raiding heron by doing that, and it kept out a lot of falling leaves. On the other hand, one spring we were a little late in removing the net and we found a dried up frog tangled in the net when we started Spring maintenance. No telling how long it had been there. I thought it was quite dead, but my husband carefully removed it from the net and dipped it into the pond water and set it on a stone. Ten minutes later it was revived and jumped into the pond–! We haven’t used a net since that time.

    • says

      I’m with you, Dahlink, re: the net. I don’t use it because birds or frogs always get caught. Horrible to see.

      Thanks, Dee, for your fish/heron feedback. I have comets only in my smaller pool that is less out in the open (near some big evergreens), no koi. And yes, yes, yes re: the right size heater! Algae is much unwanted, especially then.

  7. Dee says

    Becky, we had the same problems with herons; it was an awful sight watching such a majestic bird winging away with my biggest koi. Tried several things — including sinking a strawberry pot for hiding places. I was afraid it would crack if it stayed there all winter, so I sunk a couple of grates, propping their edges up on pots and rocks and things. The rest of the year, they can hide under the waterlilies. Mostly I’ve just surrendered — we have a couple of comets and a couple of goldfish, and seems to be enough. A friend once told me that koi were stupid and slow, which made them an easy meal for a big bird. Guess she’s right…

    Also, about the pond heater thing, it’s important to get the right size. A mid-winter algae bloom is plain freaky.

  8. Dahlink says

    We started out with koi given to us by a friend with a very prolific pond, and we added some fantail goldfish. The biggest koi got plucked off, one by one, by either herons and/or raccoons. I suspect that the remaining fish are a mix of koi and goldfish, but they reliably produce baby fish year after year. My favorites are the black koi–my “stealth” fish!

  9. Lorie says

    My water feature has to “come in” each fall, but that is a small price to pay for the joy it brings for 6-7 months with absolutely no maintenance except for adding water when the birds get excited.
    An on-the-ground shallow bird bath with a heater, and a stable rock for perching, will bring feathered wonders to the yard.
    A trick I learned while working at a bird feeding store…since you can’t just plug in your heater to see if it’s working, put it in the freezer for a bit, take it out and immediately plug it into an outlet in the house. It’ll “flare up” to the touch just enough to let you know if it’s working.

  10. Constance Stachelek says

    I have passed your comments on the my husband. We have an ongoing discussion about how to winterize the small garden pond each year, with regard to the pump and filter. Thanks so much.

  11. Laura says

    It’s our first winter with a small pond so we’ll be watching it carefully. We have as many frogs as fish in the pond and quite a few snakes that live around it. So far I’ve only seen them catch one frog and the fish hide in the submerged overturned milkcrates.

  12. luise h. says

    I have had the same heater as yours for years and I leave the waterfall running. And I also do not get to frantic about cleaning and disturbing the natural balance of the pond.
    My biggest problem is a Heron that thinks of my pond as his dinner table. I moved a metal Heron sculpture to the front of the pond last year because someone told me they are territorial birds. And to my surprise it worked! No Heron visits this winter!

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