Even a small patio can have a fish pond

When Ann and Glen Gage downsized from an expansive home and garden to a San Francisco town house, one of the things they missed most was their koi pond. It was brimming with elegant plants, fish and its own ecosystem.

So they built not one but two container ponds, this time city-style.

“If you have limited space or want an interesting water feature … patio or container ponds are an easy option,” said Marc Hachadourian, Director of the Nolan Greenhouses for Living Collections at the New York Botanical Garden.

The Gages assembled their container ponds using large planters, which they made water-tight by caulking the drainage holes. They added gravel and a few larger rocks, and filled the container with water. They added an electric bubbler and filter, “to make the fish happy.” Next came a few floating aquatic plants, which they harvested from a pond in the area, and a variety of “rescue fish” from a pet store.

“It couldn’t have been easier,” said Glen Gage.

Maintenance involves only refilling the container to replace water lost to evaporation.

Although some people put mosquito-killing tablets in the water, experts say a few small fish are sufficient to take care of insect larvae.

Although the patio ponds can look and feel like miniature koi ponds, koi experts strongly suggest goldfish as the better choice.

Unlike koi, which grow large and need plenty of oxygen and moving water to thrive, goldfish and some other smaller fish are hardier and better suited to patio ponds.

The International Water Garden Society is a good resource when deciding on varieties of aquatic plants. Plants like water lettuce and water hyacinth float on the surface, control algae and help filter the water. Aquatic grasses, irises and taro are also good choices.

When deciding where to put a patio pond, first consider how much weight your floor or terrace can handle. Even the lightest container is heavy when filled with water, which weighs just over 8 pounds per gallon.

“It’s not what you’d want on a rickety porch,” Hachadourian said.

Ponds also need a good amount of light and work best outdoors.

Although container ponds work year-round in warmer climates, they are more challenging where winters are harsher. Hachadourian said most container ponds, or at least the fish residing in them, need to be moved to a warmer area in winter.

“A lot of people treat patio ponds a bit like annuals and restart their ponds every spring. They just transfer the fish to an indoor aquarium in winter and drain the container pond. In the spring, fast-growing aquatic plants are installed, the fish are put back in the pond, and you’re all set for the warmer part of the year,” he said.