Dreaming of ponds... and wetlands

‘Tis the season to daydream… of garden ponds and other summer projects. Although I already have a small pond, I’m planning to dig another one – and there have been some lessons learned since my first venture in 2004.

First lesson: no fish. As my interest is in supporting wildlife – particularly frogs – stocking the pond with goldfish was a mistake. The fish eat the frogs’ eggs. The prevailing wisdom is that you need fish to keep mosquitoes under control. That’s not true, despite dire warnings to the contrary. You need to make your pond attractive to other predators interested in mosquito eggs and larvae, like dragonflies and damselflies (whose larvae are also eaten by fish) and, of course, frogs.

A dragon/damselfly pond should be in sun for at least six hours a day and should have varying depths of water, for submerged plants that will provide habitat for the nymphs (pre-dragonflies) and for emergent plants that the nymphs can climb out on and the dragonflies can perch on. 

Don’t let anyone sell you mosquito fish (Gambusia holbrooki). Despite their name, they don’t provide any greater control of mosquitoes than other fish and they have been designated as one of the world’s worst invasive species. Fortunately, none have been found in the wild in Ontario – although goldfish (Carrasius auratus), members of the carp family from east Asia, have become established in several areas of the Great Lakes basin through intentional or unintentional releases. That's not good, because they displace native species. 

Second lesson: no need for a pump or bubbler or fountain to keep the water oxygenated and free of algae. There are plants that will do the job, so the pond does not have to depend on electrically driven gadgets. These plants are known as submerged oxygenators and the one I have, Canadian Pondweed (Elodea canadensis) is easy and requires no maintenance. I think I grabbed a bunch from a river while canoeing somewhere. Tie the roots to a small rock and let it float down. It will grow up to the surface where it will produce tiny flowers in summer – and it will spread. Every couple of years I take out large handfuls to keep about a third of the pond open so I can observe what’s going on.

A word of warning: many plants sold as oxygenators - Water Hyacinth (Eichhornia crassipes), Water Lettuce (Pistia stratiotes) and Water Soldier (Stratiotes aloides) are invasive, crowding out native species in Ontario lakes and rivers. 

Third lesson: Plan a sitting / viewing area as part of the pond project. In the first year, visibility wasn’t a problem, but as plantings grew up, I found myself increasingly cut off from the pond activity that had been so absorbing in the first couple of years. I started opening up the space last year and this year I’m going to make sure there’s plenty of room for the people to sit and watch the frogs as the frogs sit and watch the people. Another mistake was not bringing the pond liner up high enough above my planned water level. The liner around the edge is concealed by large and small stones, but I still left it too low. A few large flat rocks, by the way, provide good basking places for amphibians and insects.

Fourth lesson: An artificial pond does need some sort of electrical input for the winter, to keep a patch of ice open, otherwise toxic gases build up and kill everything that’s spending the season underwater. We use a pond de-icer regulated by a thermostat, which we figure uses the least energy of various options. It’s plugged in all the time that there’s ice cover and birds come to the frozen pond to drink from the small opening. One year we lost the whole fish population. I think a layer of ice formed about a foot underwater, so while we thought all was well, they were trapped lower down. It was a sad spring when they all surfaced. I was consoled by the donation of a friend’s seven goldfish – which have stabilized at a population of around 40 which I suppose is what the six by 12-foot pond supports. I’m fond of them and won't get rid of them, but if I was to start again, I wouldn’t have them.

Fifth lesson: Native pond plants are the least trouble (no special care for winter) and they look terrific. In the water, Pickerelweed (Pontederia cordata) is my absolute favourite and would be the plant of choice if space restricted me to just one. Also, Fragrant Water Lily (Nymphaea odorata), the one I’d have if space allowed for two. I also have Broadleaf Arrowhead (Sagittaria latifolia) and Lizard’s Tail (Saururus cernuus). All these submerged plants are in soil in pots sunk into the shallow end of the pond.

At the water’s edge, I have Blue Flag Iris (Iris versicolor), Cardinal Flower (Lobelia cardinalis) and Spotted Joe Pye Weed (Eupatorium maculatum) along with Rosa Virginiana, Turtlehead (Chelona obliqua) and Swamp Milkweed (Asclepias incarnate). Now you know why I can’t see what’s going on in the pond – and I have still more plants I want to get in there – Smartweed (Polygonum) and Sweet Flag (Acorus calamus), to name just two.

Fifth lesson: Wait for them to come. I was delighted to have frogs, dragonflies, water striders and water snails all appear by themselves. What fun it was to see an Eastern Garter Snake swim across the small pond. A Great Blue Heron visited on a couple of occasions, much to the dismay of the goldfish who refused to show themselves for several days afterwards. Let the creatures find their way and don’t disrupt wild habitat to import what you think should be in your pond. Especially do not move turtles – they are territorial and it is cruel to take them from where they belong.

Tomorrow is World Wetlands Day. For all the value a backyard pond can provide, it is nothing to a wetland, which cleans and stores water, and is a breeding powerhouse for fish, birds and amphibians. We’ve lost more than 72 per cent of southern Ontario’s large inland wetlands – it’s time to reverse the trend and treasure what is left of these rich ecosystems (locally we are so lucky to have Wye Marsh and Tiny Marsh, two huge and wonderful wetlands). Happy World Wetlands Day!

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