Gardening columnist

I once purchased some shrubs from a nursery halfway to Baltimore, brought them to my suburban garden and, lo, found a tree frog in a thicket of branches.

It was not one of the starkly striped or spotted poison dart frogs of South America, but it was a luminous green creature nevertheless. I took it as some exotic interloper — this added to the thrill — though I later discovered there are many species of tree frog in our region, and this was Hyla cinerea, the green tree frog. Excitement turned to regret when I realized that I had taken this frog on a wild ride in the back of a pickup. Racing along the Capital Beltway is an ordeal enough, but imagine doing so clinging to a branch. Now it was marooned in Alexandria.

I have a large fish pond that should have relieved some of its loneliness, except the pond has never drawn frogs in more than 15 years. This is vexing. I like frogs and I’d love to have them as part of the wildlife mix that is the hallmark of a vital garden. Friends who have built ponds end up with frogs; they just show up.

Frustrated by this, I once raised a bullfrog from a tadpole. It grew to about the size of a Fiat and then left. There’s gratitude for you. Perhaps my pond is too isolated from other frogs to attract them; perhaps its vertical walls are too foreboding. Frogs like a beach, which is a gentle bridge between the two worlds they inhabit.

I’ve come to terms with my froglessness. What would be more worrying would be to have frogs show up for several years and then disappear. This is what happened to a reader in Northwest Washington who called to say that she had had tree frogs for years but that the last two years have been silent.

Frogs are the canaries in the coal mine for our environment. (istockphoto)

I mentioned this to Wayne Hildebrand, who helps coordinate two volunteer efforts in Maryland to keep track of amphibian populations, the North American Amphibian Monitoring Program and the Maryland Amphibian and Reptile Atlas Project. Volunteers are invited and will learn to identify frog species by their calls, which, if nothing else, might make you the life of a party.

Amazingly, Maryland is home to four toad species and 16 species of frogs. The fauna range from the barking tree frog, which is endangered, to that ubiquitous Kermit of fish ponds and lakes, the northern green frog.

For sheer beauty, nothing beats the pickerel frog, no more than three inches long but with skin markings akin to a python’s. I think the frog I would most like to meet, though, is the wood frog, handsome in its warm gray livery and dark eye mask.

I asked Hildebrand what could have happened to the reader’s tree frogs. Tree frogs, in spite of their names, need ponds to breed. A colony might die off, he said, if the body of water they rely on dries up, disappears to development or becomes polluted.

We need to worry about frogs. Frogs are the canary in the coal mine of our environment. They breathe through their skins and absorb the poisons we put in the water, air and soil.

Researchers believe that common pesticides, and even nitrogen fertilizers, are harming frogs and toads. One study showed that the widely used herbicide atrazine indirectly increased snail populations, giving rise to a snail-borne parasite that killed frogs. DEET, the active ingredient in many bug sprays, is highly toxic to amphibians. Don’t spray your hands and then go looking for frogs to pick up.

Frogs offer us another reason to garden organically — and even then we should keep natural nutrients away from any pond or stream. My experience notwithstanding, the installation of a pond will probably bring you frogs. Put in a few small fish to eat mosquito larvae, and make the pond large enough so it doesn’t freeze solid in the winter.

Hildebrand has put in three ponds on his one-acre lot in Keymar, Md., near Frederick. He has logged the arrival of several species, namely the green frog, bullfrog, pickerel frog, American toad, wood frog and spring peepers.

The call of most frogs is, as with songbirds, the male serenading a mate. Some tree frogs offer a different call when they are high in a branch, luxuriating in a deluge. “During a rain you may hear them calling,” Hildebrand said. “ ‘It’s rain. I’m happy.’ ”

Follow Adrian Higgins on Twitter and read more about gardening here. You can check out videos of Higgin’s at his community garden plot at