Constructing our wildlife pond
Because we were concerned about the goldfish in our original pond eating dragonfly and frog/toad eggs, we decided to build another pond - this one strictly for wildlife. This pond is shallow and has lots of room for marginal plants. It's between the original pond's sitting area and the house in one dimension and between the garage door and the porch path on the other - about the only convenient space left for a pond. One interesting aspect of this placement is that the outer sides of each pond are in alignment, so that it almost appears that the sitting area is on a bridge between the two ponds. And since this pond abuts the house, you might think the house is floating on water. (My husband has already stated that he's not about to build another pond along the front of the house to complete the illusion, however!)
Since most ponds are designed just to be ornamental, there has been a lot less guidance for designing this pond. It's been an ongoing experiment, and we've been designing as we go along. By the way, there seems to be much more interest in this kind of thing in England, even with special clubs just for dragonfly ponds enthusiasts.
To provide a place for frogs to hibernate, we created a large hole in the middle which was lined, then filled in with soil so that the ultimate depth is just under two feet. After using a lot of extra liner to make this deep pocket of mud, I learned that frogs don't actually bury themselves deep in the mud, so it wasn't necessary. Having a hole in the ice is necessary, though, and we've had some problems with that some winters, so we've lost some of our frogs some years. This year, we're experimenting with a PVC pipe being left in each pond so there is a place for air exchange. I check it each morning and pour in some warm water if it has iced up. We're waiting to see how they do this winter ('09) which so far has been a very cold, very snowy winter. If they don't make it this winter, we'll have to come up with some other plan - preferably not requiring electricity.
Because we won't have moving water in this pond, we originally planned on using mosquito dunks - Bt pellets that kill mosquito larva. Unfortunately, it also kills other larvae of the fly family as well. Each pellet covers up to 100 sq. ft. of surface area and lasts one month - quite easy and affordable for about $2/month. Because we're in a urban/suburban area, we felt we needed to take this precaution. As it turned out, though, after the pond was established, there were so many things that eat mosquitoes and their larvae (birds, frogs, toads, and dragonflies, etc.) that we haven't had a mosquito problem. In fact, we seem to have fewer mosquitoes than in our pre-habitat garden days.
Constructing our Wildlife Pond - 2003
First, we reinforced the sitting area next to the original pond. Our yard slopes toward the house, which was a real advantage for our first pond since it made the stream look more natural. For this pond, though, that means that the lowest point is at the house, so it made the area behind the sitting area that much higher when we dug it out to be level with the lowest point.
Our main problem was to figure out how to hold back the soil next to the sitting area in a safe and inexpensive way. A regular retaining wall would have worked, but would have been much pricier. Our solution was to use pressure-treated lumber held in place by posts set in concrete. (Afterward, it occurred to me that we shouldn't be using treated lumber which is treated with toxic chemicals, but in this case I hope that there will be no damage since it will not be adjacent to the water and it mainly is a mulch-covered sitting area. From now on, though, I won't be buying any of this type of lumber.)
We split the difference and reinforced the top two-thirds of the bank with treated lumber. The bottom third juts out some and is pretty solid since it's the original soil about two feet below the original surface. We're using this one-foot-wide area for planting.
This shows the stones supporting the bottom third of the wall - actually pieces from our neighbor's sidewalk ("urbanite") that they were replacing. We filled in the spaces with sifted soil. You can see the original pond in the upper left corner. The sitting area appears (with a little imagination) to be on a bridge of land on top of one continuous body of water.
Another use for sifted soil - adding water to turn it into mud to cover the sharp edges of shale. Our yard has a lot of shale beneath the surface. This has been a real difficulty with both ponds. We've ended up with a lot of stone debris - but stone debris that is pretty useless for anything since it's so brittle. You can also see the planting pocket for a water lily at the upper left of the big hole. The standing brick indicates the probable maximum water level. It's important to keep thinking ahead as much as possible when you're designing a pond.
We then spread the underlayment and the PVC liner. We used PVC for this pond as opposed to the EPDM 45 mil we used for the first pond. The PVC is advertised as being stronger even though it's thinner. It was more expensive so I hope they're correct.
We filled the pond with water to see where the folds were going to go. We then emptied it (using the water to water our front bushes).
We added sifted soil, some large glacier boulders for stepping stones (since I didn't have room to leave a path), and we started to add stones. We bought large flat stones to line the wall of the deep hole in the middle.
After adding soil, we added kitty litter - yes, kitty litter. Why? Because it's just pure clay. We made sure we didn't get any with deodorants etc. added. We added this to try to keep the soil in place. Was it a good idea? We don't know yet. I thought we'd do this because that's how we had created the lily planting pocket in our original pond. On the one hand, we're trying to create a natural pond; on the other, natural ponds develop naturally, not with a liner so I feel we can make some of these adjustments. We had to experiment since there's very little guidance available for this type of pond.
Since the bagged stones were very dirty with who knows what kind of dirt, we decided to wash them first. We also removed any sharp pieces of stone.
Here's the pond the morning after we filled it. We had to make some adjustments so that the water will move farther up the pebble beach in the upper right corner. We hoped that putting kitty litter in was a good idea - the water was still pretty murky, but it settled out. We stuck a few plants in and a piece of driftwood just to get an idea of what it will look like. We also added a mosquito dunk. At this point - before plants and animals moved in - the mosquito dunk was indeed necessary.
We put mini sandbags (sand inside the long plastic bags our newspapers are delivered in) along the back wall for added stability and to prevent overflow. We then pulled the extra liner around the sandbags.
The day after filling the pond, a dragonfly landed on the driftwood and laid eggs!
Another issue was how to deal with overflow. We're fortunate in that even though it looks like it's right against the house (and it is), this part of the house is a family room converted from a garage, so our basement is actually about 15 feet away. If the pond does overflow, it's unlikely to reach the basement.
Here's our solution. We laid some pipe at the edge of the pond in front of the door and ran it to the other side of the door sloping up. So far, it works. The photo shows the workings of this overflow system, but we covered with a stone, so it's not noticeable. It's important to have an overflow system, but the reality is that it's rare that it rains so much that the water builds up to overflow level. Keeping the shallow pond with a large surface area filled is the bigger problem.
Here's what it looks like as it's developed.
For more info
It's not hard to find information about creating an ornamental pond - they're very popular ... and profitable. But it's a different story for wildlife ponds. Here's some more information I found:
- Cooperative Extension wildlife pond
- Ponds and Water Gardens - also has information on creating and maintaining a bog
- Biggs' Wildlife Pond - a wildlife pond in California ... that led to writing a book on dragonflies!
Last updated 02/05/2009
