Cleaning up after the visitors in your pond

Duane Campbell

Three frogs are living here, like the three bears – a big one, a middle sized one, and a tiny one. The big one, Thaddeus, has a lime green head and a pinkish body. I sent a picture to a professional herpetologist (I suppose there are stranger ways to spend your life, but I can't think of any at the moment) … where was I ...oh, he told me it was a common northern green frog, and though they are variable, this was admittedly unusual coloring. He may have been just trying to mollify me for asking a dumb question.

Uninvited but welcome residents, they live in my lily puddle, a preformed pool in the ground that holds maybe a couple hundred gallons. Tiny. And they share this space with roughly fifteen fish. I haven't been able to get an exact count. Fish don't hold still. It started with three fish, but you know how fish are.

These are humble goldfish. Pretty goldfish, a little fancy, but still just goldfish. When I first installed this small pool, I had to do the trendy thing. I got some koi. Koi at whatever size go for 10 or 20 times the cost of similar size goldfish, and that gives them a sense of entitlement. They get rowdy, stir up mud, tear up plants. Koi are thugs. After a couple of years of this, I replaced them with better behaved fish.

My little pool has a population density resembling Tokyo. Tokyo has a sewer system. My pool does not. Fish and frogs produce … um, what we gardeners call organic fertilizer.

Here's how it works. The pond water quickly becomes a nutrient rich soup. Sun, warm water, and nutrients are the perfect environment for algae, and the water turns pea green. Many install expensive filters and regularly engage in the inspiring job of cleaning them. Often they still get green water.

I have no filter. I have no green water. And the reason is not only simplicity itself, it is beautiful.

As the hormone supplement ads tell you, it's all about balance, except with ponds it's really true and it really works. You need water plants to absorb what the fish pump out, to eat up the nutrients in the water. If you have green water, you have either too many fish or lazy, small plants.

Cattails are great nutrient suckers for large ponds and water lilies for medium sized pools, but my puddle is too small for either. I have a couple of plants that are attractive though not very efficient at nitrogen removal, but the one that keeps my water clear is variegated sweet flag, Acorus calamus variegatus.

Sweet flag is the perfect plant for small pools. It is hardy, so you don't have to replace it every year. It is vigorous but not invasive in a lined pool. If the nutrients increase, it increases and compensates. The root system provides breeding ground for the fish and protection for the fry and fingerlings.

And it is easy. Just break off a piece of a friend's flag (drop by) and plant it in a small pot with poor soil, not the richly amended soil from your garden. (I grab a trowelful from a neighbor's garden.) The roots will quickly escape the pot, which is a good thing.

Lotus are also reputed to be good for this, and I'd like to tell you my experience, but I have none. I have always wanted a dwarf lotus for my dwarf pool, but I've never seen one in garden centers, they are often sold out in catalogs, and besides, the catalog prices cause my check writing hand to shake.

(Finally for those itching since the first paragraph to send me a hypercritical e-mail, yes, I know that Thaddeus was a toad, not a frog.)

Duane Campbell is a nationally known agricultural expert. He can be reached at 12 Burgess Drive, Towanda, PA 18848 or e-mail

comments powered by Disqus