The koi pond at the National Arboretum. (Adrian Higgins/TWP)
Gardening columnist

Night and day, winter and summer, the ornamental carp wander aimlessly in the dark waters of the National Arboretum’s outdoor koi pond. Some of the biggest fish have been gliding this way for decades. On Thursday they must begin a new journey.

The pond, built as a glassy apron to the arboretum’s administration building, needs major renovation. The building, a faded jewel of modern architecture, is undergoing its own separate restoration, but the pond rehabilitation follows and will take a year or more to complete.

This leaves the koi keeper, Bradley Evans, in a quandary: what to do with more than 200 fish.

The answer will play out this Saturday, when folks with garden ponds are invited to one of the most unusual liquidation sales around. Koi prices range from $1 to $150, depending on the age and size of the carp.

The arboretum has had sales of its surplus fish before — the last in 2010 — but this is the first time that virtually its entire stock has had to go.

The koi pond’s curator, Bradley Evans. (Adrian Higgins/TWP)

Evans and his colleagues and volunteers will save just 15 or so of the largest fish to keep in a temporary tank until the pond can be restocked. They will include the queen of the pond, the only named fish, a lumbering titan called Big Mama. Volunteer Dick Hammerschlag estimates her weight at 30 pounds.

If all goes to plan, the team will close off the pond and its adjoining terrace this week, unplug seven drains and wait until Thursday for the water level to drop to a mere three or four inches, when the crew can net the beached koi and place them in eight temporary tanks. Full, the pond is about 32 inches deep and holds 115,000 gallons of water.

Koi are big and needy, doing best in large ponds with robust aeration and filtration systems. If you have a small, kidney-shaped backyard pond, my advice would be to stick with goldfish or mosquito fish.

“I just hope people don’t come with the idea of putting koi in an aquarium,” Evans said. I caught up with him and Hammerschlag the other day. Both of them were in waders and finishing the work of removing the potted aquatic plants, including hardy lilies, the tender papyrus and Thalia geniculata, a striking plant with big, spearlike leaves and long wiry flower stems.

Evans won’t know until Thursday how many fish are in the pond — they have a tendency to reproduce. He estimates that there are about 100 mature fish of 12 inches or longer and as many as another 200 juvenile koi.

There is no question that a koi pond can bring beauty and animation to the garden. The fish themselves, apart from their varied markings, are quite different in character. I’ve kept koi for 18 years. Some are skittish and dart to the pond floor when you arrive, and others will feed out of your hand. Most are indifferent to everything except their own looping peregrination.

At the arboretum, the larger fish seem to enjoy breaking the surface with their dorsal fins and then sinking a few inches into the gauzy water (made murky by the current pond work and a decorative black dye). Big Mama, who is entirely golden and unmarked, doesn’t run with the rest, swimming her own isolated courses.

As koi go, the arboretum specimens are not of high show value. Fanciers are drawn to fish with markings and colorations that are not only beautiful, but exemplars of types. Breeders and hobbyists lump them into such categories as Kohuka, the classic white with orange-red splotches, or the white, orange and black calico effect of the Showa. The Matsuba class has a pronounced gray shading to the scales.

Some of these prized fish can sell for $1,000 or more, a fact that might keep the owner on edge when it comes to problems with water quality, fish disease, the arrival of a heron or a prolonged summer power outage like the one we experienced in early July.

Just as a mutt can give as much joy as the most handsome show dog, the less exalted koi lend the garden movement, serenity and sheer enjoyment.

These wonderful animals at the arboretum now face mass dispersal, but the sale offers survival for the fish and a bargain for their new keepers.

@adrian_higgins on Twitter

Read past columns by Higgins.

Surplus koi sale

U.S. National Arboretum, 3501 New York Ave. NE, Saturday, 9 a.m. to 2 p.m. Preview 8 to 9 a.m. Cash or check, no credit cards. Bring a cooler to transport larger fish (202-245-2726).