Back to Gardening Chapter 4, Design - Part D: A Tale of Three Ponds (final installment)

In this section of Chapter 4, I share my lessons learned from ponds I've made in my backyard, and then I summarize all the ways that ponds are good for gardens.

I ended the last section speaking to how well Pond 3 did in it’s first year. Indeed, in a matter of months it went from being utterly lifeless to looking like it had been there for years. Still, one thing did go terribly wrong that summer, but despite that mishap, there was a wonderful surprise the following spring…

A frog too far

By the end of summer 2023, Pond 3 was teeming with life. In fact, I had almost a dozen frogs in residence, and every week they got a little bigger. I considered these new pond guests to be a sign of a healthy system, but I had forgotten one thing: carrying capacity - a term used in biology that refers to the maximum population of a species that a given environment (and its resources) can support.

Perfect camo! These Northern Green Frogs loved my pond. I don’t know what they were eating, but they got bigger every week!

I already had ten or eleven sizeable (3 - 4”) goldfish living in the pond at the same time. By rough estimation, I’d say the pond had a maximum volume of 240 gallons of water (4 bathtubs). A rule of thumb for goldfish is that each fish needs about 20 gallons of water. Therefore my pond was already at it’s carrying capacity BEFORE the arrival of the frogs. As the frogs grew and grew (and defecated, and defecated), the water started to change. It was hard to notice at first because it was always a bit muddy, but one day I came out and there was foam on the pond. At that point I decided that the nutrient levels must be too high, and the water was either at or approaching nutrient levels that might be toxic for fish.

Lesson 20: While 20 gallons of water is enough water for each fish, allowances should be made for other organisms that might take up residence in the pond - like frogs…

Rather than try to figure out what to add to the water to balance things out, and wait to see what happens over the next few days, I took a more expedient approach, and siphoned off 2/3 of the water in the pond. I then refilled the pond with fresh water from my garden hose, although one good rain would have also done the job. For the rest of the summer and fall the pond was fine.