Sun loving water lilies provide shade

Water Garden FAQ’s

Sometimes we come across issues in our water gardens that worry or perplex us. Here are some common questions we are asked in everyday water gardening, and advice on how to remediate, from our expert, Ken Bernard.


Why has my water garden turned green?  This is caused by excess nutrients in the water.  Cut back on fertilizer, remove decaying vegetation, and stop feeding the fish.  Create more shade by adding more floating plants or surface plants, check your water clarifiers (oxygenators), and be sure your fish and snails are okay. Note: String algae, a green filamentous type of algae that forms into slimy strings is a good sign in a pond and in a water container garden.  This is one of the signs of water maturity.  Remove 60 percent by hand but be careful to not remove all of it. 


Where have my fish gone?  Look for a stalking cat or signs of a bird perching on your water container.  Dragonfly Larvae are famous for eating small fish.  The water may have gotten too hot, so create more shade.  Add one or two small fish (we love platies) and try again.  Sometimes a young water container garden has a hard time supporting many fish in the beginning.  If your container is inside the house, you will need to feed your fish a little.  If your container is outside you should never feed your fish.  Let the fish eat mosquitoes, mosquito larvae, water bugs, aphids, and algae.  Then you have a healthy mosquito trap that will cut down on mosquitoes in the area.


Why is my water starting to turn black? This is a sign of too much rotting vegetation in the container, a dead toad, or dirt that has turned anaerobic.  Your fish will die soon if you see this happening, so take action.  Remove rotting vegetation and change the dirt in your pots if it smells soured.  Add more floating plants, and add water clarifying plants before emptying the water.

Should I change the water? Only as a last resort.  If you do, always save some of the old water to add to the water garden.  Be sure to follow the above instructions and take action to correct the original condition that caused the water quality to change.  Most containers with new water need to go through the progression of algae blooms for maturing the water.  The more mature the water is, the less algae blooms you will have to navigate, so dumping out the water means starting over again.

What do I do if insects are eating my plants? Snails and slugs can crawl up your container and get to the plants that touch the edges of the pot.  They can crawl across the bridge of lily pads and munch along the way.  Putting a circle of copper tape at the base of the container can stop the snail and slugs.  If the snails are bad water snails (the ones with pointy shells), then you can pick them off and remove egg cases under the leaves and on the stems.

Why are aphids are attacking my lotus, my water lilies, or my bog plants?  Use your fingers, squashing some of them as you remove them and put them on the water surface.  Your fish will love you for this and will have a special treat.  Do this daily until the problem has balanced itself out.  Aphids normally attack weak plants, so fertilize your plant being attacked and talk to it as you remove the aphids.  One can also control aphids by mixing a small amount of dishwashing detergent with vegetable oil in water and spraying it on the plants.  Then use a hose to flood the oil off the surface of the water to prevent smothering your fish (oxygen is blocked by surface oil on the water).

Why do I see holes in my lily pads and bulges in some of the stems?  You have a China Mark Moth or borer at work, and you need to take action.  Moths, birds, frogs, and toads can bring pests to your water container ponds.  You can prune severely until the problem disappears or spray BT (bacillus thuringiensis, Dipel) daily until the problem is under control.

Why are my plants are turning yellow prematurely?  Some plants may react this way if they are getting too much sun. Water lettuce is famous for turning yellow if it gets too much sun.  They may need fertilizing or might be getting too much fertilizer.

What do I do if a plant that I do not recognize is taking over? Invasive water plants that are considered the weeds of the water gardening world include Duck Weed, Bladderwort, Pond Weed, Fairy Fern, and Salvinia.  They have good qualities such as creating shade coverage and water filtration, yet they can really be a pest by over-growing and smothering other plants.  See our blog post about invasive species here.

Why is my water lily not doing anything?  Do not fret. From December to March many water lilies can enter dormancy. If you have a variety that is prone to dormancy you will notice the leaves getting smaller and blooming will cease.  Let it rest and do not fertilize it.  Resume monthly fertilization in the spring. So long as your lily is getting enough sun, it should be able to bounce back.  If your lily has continued growth over the winter and is a tropical variety, continue fertilizing monthly to encourage blooms.

What do I do if I think my water lily is dead? Not a problem. It happens to the best of us. Bring it by and we will repot it for you for $15 if it is rescuable.  Otherwise, we would suggest you purchase a new one. We are always propagating lilies and have a vast assortment of lilies that bloom year-round and have many at the nursery available for sale that have not skipped a beat. Perhaps your water garden could use a fresh lily, clarifying plant or fish? Most importantly, do not give up, we are here to help!

Additionally, we would like to announce that we have our annual lotus class scheduled for February 27. You can register here.

Be sure to stay tuned for more information on our Lily 101 class in March. Garden Ponds is located beside the Kaua’i Mini Golf in Kilauea. We are open Wednesday to Sunday 12-5pm and you can visit our website at or call us at 808-828-6400 for more information.

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