Gardening Help FAQs

Here are answers to some of the most common questions we receive about garden plants. You will find concise information on general gardening techniques as well as plant selection and care. For detailed information on specific plant pests and problems refer to our Common Garden Pests and Problems page.

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Horticulture Questions and Answers

How do I raise koi fish in my water garden?

One of the most popular attractions at the Missouri Botanical Garden is, surprisingly, not a plant. Visitors, especially those with children, who make their way to the bridge in the Japanese Garden, are captivated by the sight of massive, brightly hued fish congregating at the first sound of the fish food dispenser.

These are Koi, also called Japanese ornamental or brocaded carp and they have long been a feature in Japanese gardens. The first written reference to raising carp is in a Chinese manuscript dated 470 B.C.. The earliest documented reference to Koi culture in Japan was in 714 A.D.. Over centuries, the Japanese have bred Koi to display brilliant colors in varied patterns. For example, a specimen with a blue back and red belly might be described as "autumn sky over red maples". There are varieties with a highly metallic sheen, as well as the aptly named mirror (or German) carp which have a few very large iridescent scales. These robust fish have come to symbolize courage, strength and masculinity. On May 5th, Boys Day, Japanese parents traditionally fly paper or cloth carp banners to represent each son in the household.

With an increased use of water features and oriental themes on landscaping, Koi have gained popularity in American gardens. Once difficult to purchase, they are much more available in recent years and are highly valued for their bright colors, hardiness, and fast growth. Large, well-marked specimens command high prices among collectors.

Water in the landscape is a magnet for people, birds, insects and other wildlife. Fish play an elemental role in garden pools. They bring color, life, movement, and, more importantly, they devour mosquito larvae.

Fish for an outdoor pool should be hardy types like Koi and goldfish. Look for healthy fish--those that swim strongly, keep fins splayed and have clear eyes and intact scales. Goldfish have been bred for varied body shapes rather than color, with the more extreme forms being less hardy. Standard goldfish and comets are reliable standbys and are better suited than Koi to very small pools or tub gardens.

Establishing a pool to keep Koi requires good planning to ensure adequate oxygenation. In very hot weather, water holds less oxygen; and, if it is cloudy, plants release little oxygen. When these conditions exist, fish can suffocate and die. A bubbler or simply a garden hose slowly dripping onto the surface of the water will help.

In winter, a solid ice cover can trap toxic gases from decaying leaves or debris. This can be prevented by removing leaf litter in the fall and by maintaining open water to permit gas exchange. The pool can be covered by an insulating material like plywood topped with straw. A sheet of plastic keeps the straw dry. A new product--thin, flexible styrofoam sheets can prove useful instead of straw. A stock tank heater placed in the pool will also keep an area ice-free.

Koi are scavengers and will find many things to eat, including algae and insects but they thrive on commercial Koi pellets. Floating pellets reduce the likelihood of food sinking and spoiling on the bottom. They also permit the fish to be seen and easily tamed. With patience, Koi readily learn to feed from a person's hands. In a small backyard pool, you'll have to be wary of overfeeding these aquatic beggars.

If you lack the desire to keep a pool and fish of your own, you can delight in the beauty and grace of these living works of art by visiting the Japanese Garden at the Missouri Botanical Garden.