Spring Cleaning the Water Garden
by Leonard Perry
by Leonard Perry


In extension I serve as an advisor and consultant to the greenhouse and nursery industry, primarily in Vermont but throughout the region and beyond as well.

I give presentations on my research to the industry, and to home groups. In Research, my focus is "herbaceous perennial production systems".

His website is at  Leonards zone of gardening: home with my trials, generally USDA 4a. Campus in Burlington is 5.

April 8, 2012

If you have a water garden, other than a large pond, spring is the time to evaluate if it needs cleaning, and to do so then before life in it fully resumes. If there is sediment build up on the bottom (a half inch or more) and leaves floating on the top, and the water is murky, cleaning will help keep fish healthier and unwanted algae from growing.

Evaluate your water garden after spring thaw occurs. If you have been diligent about pruning plants and skimming, you'll only need to drain the pool or pond every three to five years. If you like pristine clear water, then cleaning yearly may be needed. Never drain it more than once a year, however, and ideally when temperatures are below 55 degrees F. Water gardens have beneficial bacteria that keep algae in check, and below this temperature they aren’t yet established. Cleaning out the water when warmer may disrupt this balance, with the water going “green” before the bacteria build again to sufficient numbers.

If you have a simple plastic tub with no fish as I do, you can simply drain and clean it, before refilling. I just use a pail to get most the water out, then a plastic dust pan, scoop or old sponge for the rest. If you had any plants left in over winter, remove them to a place out of sun and keep moist (a tray or pan with water works well, or moist newspapers over the top) for the short time you’ll need for cleaning. If you had water plants that love warmer temperatures, and didn’t hold them over winter indoors in pans of water over 50 or 60 degrees F, they may need replacing. Depending on the amount of decomposed debris, you probably can use a net to clean small pools. For larger ponds, or where a lot of debris has settled at the bottom, you will need to pump the water out with an existing or submerged pump, or by siphoning. If you have small fish, place some screen over the hose or pump to keep them from being sucked out. You can transfer most of the old water to a clean garbage can, children's wading pool, or large buckets to be used for watering plants. Or, merely water lawns and garden beds with the nutrient-rich water.

As you lower the water level, carefully remove the plants. If you have fish in your pond, pump the water level down to about six inches, then catch them with a net. Put the fish in holding containers of the "old water," covering these with netting to discourage predators, and if koi to prevent them from jumping out. Keep fish out of direct sun, and get your cleaning done soon so they can be reintroduced the same day. They’re weak after a long winter, so you want to minimize stresses on them.

Once the pond is empty, quickly rinse the walls. Some prefer to use a forceful nozzle on a hose, rather than pressure washer, to try to leave some of the algae on the sides and rocks. This will help your pond “ecosystem” reestablish more quickly. If you have rocks and gravel buried in sediment, you may need to remove them and clean out the sediment before replacing. With the water out, check liners and hoses for leaks and repairs, and clean or replace filters.

After washing, pump the remaining water out, or use a wet/dry shop vacuum. Then refill with clean water, adding a neutralizer chemical (according to label directions), if you have fish, to hasten dechlorination. If you did a thorough cleaning, or did so during warm temperatures, you may want to jump start your beneficial bacterial with a commercial microbe product. Replace the plants, giving those that need it a trim first, repotting or dividing them if the pots are bursting at their seams. You can add fertilizer to pots, granular mixed with the soil or special pond tablets pushed into it. If you have fish, use fish-safe fertilizer pellets.

When the water temperature stabilizes, you can return the fish to the pond. Check first to make sure they are healthy, with no visible signs of disease or parasites, in which case you’ll want to quarantine them. There should be no more than a three to five degree difference in temperature between the old and the new water to prevent shock to the fish.

It's a good idea to add some hiding places for fish and frogs in the pond as a guard against predators. Pond walls that slope straight down from the sides, as opposed to gradual slopes with shallow areas, which wading birds like, also help prevent predators from cleaning out your fish. An owl or heron decoy placed near the pond may help, just remember to move it often to simulate the real thing.

Plants will keep water clear as they absorb the nitrate buildup that naturally occurs in ponds. However, throughout the summer, you will need to regularly prune plants both to control algae and enhance the appearance of the water garden. One rule of thumb is that the pond surface should be 60 to 70 percent filled with plants, maximum. Periodic skimming and netting also will keep your water feature attractive, and minimize spring cleaning next year.

Follow these steps and your water garden will be a low-maintenance and beautiful asset to your landscape, not a high-maintenance eyesore. Check local complete garden centers for plants and supplies. A directory of suppliers, plus information on all aspects of water gardening, can be found online (

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