A backyard water garden works best with a mix of floating, submerged and emerging plants, partial shade to limit algae, and plants covering no more than two-thirds of the surface. Add fish only after plants are growing, avoid overfeeding, and handle mosquitoes with moving water or BTI “dunks” rather than letting water sit still. The guidance below comes from University of Florida and Kansas State extension; Florida’s advice reflects a warm climate, so adjust winter steps for your zone.
Where should you put a water garden?
University of Florida (UF/IFAS) suggests a visible spot, such as beside a patio, with filtered light or a mix of sun and shade: some shade limits algae, but plants still need enough light. Fish ponds need at least six hours of sun a day (UF/IFAS).
How big and deep should it be?
UF/IFAS says fish ponds should hold at least 500 gallons (about 1,900 liters) and that koi need a depth of at least 3 feet (about 90 cm), with some experts recommending 6 feet (about 1.8 m). It suggests making the middle deeper and adding overhanging rock ledges to protect koi from predators. It does not give a minimum for plant-only ponds, and Kansas State does not give depths.
Which plants should you use?
- Floating: water lilies, tropical or hardy (UF/IFAS).
- Submerged: native fanwort (rooted) and hornwort or coontail (free-floating) (UF/IFAS).
- Emergent: yellow canna and pickerelweed (UF/IFAS).
- Mix all three types, and keep mature plants to no more than two-thirds of the surface (UF/IFAS).
How do you keep algae down?
UF/IFAS says plant shade limits algae because algae need sunlight. It also suggests fertilizing conservatively with slow-release tablets pushed into the soil, adding plants and rocks to host beneficial bacteria, and using beneficial bacteria or barley balls. An algicide is a last resort, and the label must be checked for safety around plants and fish. Kansas State likewise says to add barley in spring if needed and to add beneficial bacteria to reduce sludge.
What about mosquitoes?
UF/IFAS says to flush a container garden by overflowing it up to twice weekly in summer, use a circulating pump in larger ponds to make water less attractive to mosquitoes, and consider mosquitofish (gambusia) in small ponds with no other fish. It also describes mosquito dunks, which slowly release Bacillus thuringiensis israelensis (BTI) to kill larvae, as safe for plants, pets and the environment. Kansas State does not cover mosquitoes.
Do you need fish, a pump and a filter?
UF/IFAS says to add fish only after the plants have started growing, to avoid overfeeding and overstocking, and to use pumps and aeration to move and oxygenate water. Kansas State recommends starting to feed when the water is above 50°F (10°C) and stopping when it falls below that, and cleaning pump intake screens, nets and filters every other week in summer.
How do you care for it through the seasons?
| Season | Tasks (Kansas State unless noted) |
|---|---|
| Spring | Clean the pump and flush hoses, start the biofilter, raise tender plants from deep water, add early-bloom and floating plants in April and May, divide or repot plants except iris |
| Summer | Add tropical and bulb plants once water holds at 70°F (21°C); feed tropical lilies every other week |
| Fall | Divide rushes and iris; remove floaters and emergent tropicals when frost is near; stop fertilizing as plants go dormant (UF/IFAS) |
| Winter | Trim hardy submerged plants below ice level; turn off fountains and streams, clean biofilters and install a winter bubbler or deicer; never break ice by hitting it, since the shock can kill fish |
On cleaning, the sources differ. UF/IFAS advises waiting until February or March because frogs and snails overwinter in organic matter and it protects the bacterial cycle. Kansas State says to clean or partly clean the pond but never power wash the liner, whose patina hosts beneficial microorganisms.
Planning a pond? The pest identifier can help with plant pests, and the companion plant finder covers nearby beds.
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Frequently asked questions
How much of the pond should plants cover?
UF/IFAS says no more than two-thirds of the surface when mature.
Can I stop mosquitoes without chemicals?
UF/IFAS suggests moving water with a pump, flushing container gardens, mosquitofish, or BTI dunks.
When should I clean a pond?
UF/IFAS says February or March; Kansas State says never power wash the liner.
Reviewed November 2026. Sources: UF/IFAS Gardening Solutions: Water gardens; Kansas State University Research and Extension: MF2913
