July 14, 2009
Over the years of blogging about my stock-tank ponds (a 100-gallon container pond in my former garden, and this new 717-gallon one), I’ve been asked many times how I constructed them. I finished the new pond yesterday evening, so I’ll explain how I did it, from start to finish.
Setting up the stock tank
If you live in the Austin area, go to Callahan’s General Store to pick out your stock tank. If you live elsewhere, I suggest searching for farm- or ranch-supply stores on the outskirts of town or looking for a mail-order source. Stock tanks come in many sizes and can be either circular or oval. I recommend a 2-foot-deep tank if you plan to grow water lilies and keep fish.
Measure an area a few feet larger than the size of your stock tank, and dig out the grass or groundcover down about three inches. Using decomposed granite or paver base and a level (rest it on a long, straight board to check the level across a large distance), lay a flat, stable base, tamping it smooth and level, for your tank to sit on. It will be very heavy when filled with water, and you want to be sure it won’t sink on one side over time, making the water line in the pond look tilted too.
When the tank is positioned, fill it with clean water from a hose or, better, a rain barrel. If using tap water from the hose, let the water sit in the tank for three or four days before planting or adding fish so that the chlorine in the water has time to evaporate. Once you have fish or other wildlife in your pond, you’ll need to be careful about how you add water to compensate for evaporation. To top off small tanks like my old stock-tank pond, use rainwater or a bucket of tap water that has had time to de-chlorinate. Larger tanks like my new one may be topped off with water right out of the hose if it’s only an inch or two; the volume of water in a large tank nullifies the impact of the added chlorine, so long as it’s not too much.
Update 4/20/13: If you live in the City of Austin, chloramine is now added to our drinking water. (If you live elsewhere, check with your water provider to see if your water contains chloramine; many cities use it.) Unlike chlorine, chloramine does not dissipate on its own, and it is toxic to fish. You’ll need to buy a product to neutralize the chloramine in your pond water before adding fish. I bought a liquid product called Pond Prime from Hill Country Water Gardens in Cedar Park, and they told me that using it once a month would be sufficient. It only takes a few capfuls to treat my 8-ft. diameter (700 gallon) stock-tank pond.
Planting the stock tank
You’ll want to choose at least three types of plants for your new pond: oxygenators (submerged plants), marginals (water’s edge plants), and deep-water aquatics (plants that sit on the bottom and have leaves on the surface, like water lilies). Water lilies may be sexy, but the hard-working oxygenators are very important in maintaining a natural balance in the water, keeping algae at bay, and producing oxygen for fish. I like to use anacharis, pictured above. The nursery will sell it in small bundles wrapped in wet newspaper.
As soon as you get home, put the plants in a bucket of water or get them planted in the pond. You’ll need a few old plastic pots filled with clean pea gravel. It doesn’t matter whether the pots have holes in the bottom. Pick up a clump of your oxygenator plants…
…and carefully insert the bottom inch or so of the stems into the pea gravel of the pot. The stems are fragile, so I make a little hole in the gravel with my fingers, set the stems in the hole, and then bank the pea gravel around them.
Here’s a bunch all potted up. Anacharis doesn’t even have to be potted, I’ve heard, but doing so helps protect it from being devoured by the fish. The fish may eat it up over time. When that happens, just buy some more.
Place the potted oxygenator plant on the bottom of the tank, and that’s it. I bought six bundles of anacharis for my large stock-tank pond and filled three pots with them. I may need more, but I’ll wait and see if these grow fast enough to keep the tank clean.
Next you’ll need to build some platforms for your marginal plants. I use whatever is at hand: stacked bricks, overturned pots, and cement blocks.
Cement blocks with holes in the middle have the added advantage of giving fish a hiding place from predators like raccoons and herons.
I chose three marginal plants for my new pond: dwarf papyrus (brought over from my old pond)…
…’Black Marble’ taro…
…and a dark-leaved pond crinum from Hill Country Water Gardens.
Last but not least, the attention-getters for any pond: water lilies. Deep-water aquatics like these shade the water with their large, spreading leaves, helping to keep the pond cool, sheltering fish, and blocking out the sunlight that algae feed on. I brought over ‘Helvola‘, a dwarf yellow, from my old pond.
And I recently bought this ‘Colorado,’ a medium-to-large coral-pink lily. When purchasing water lilies for your container pond, be sure to note their mature sizes. Small stock-tank ponds like my old one have room for only one dwarf water lily. Larger ponds may be able to support two or three larger lilies.
Water lilies should be placed on the bottom of the tank if their leaves can reach the surface. If the leaves aren’t that long, place the pot on a few bricks to lift it up. As it grows, remove the bricks to lower the pot to the bottom of the pond. Once a month during the growing season (March or April to October in Austin), press a fertilizer tablet with your finger deep into the heavy soil of the water lily’s pot. Don’t let the tablet dissolve in the water, or it will contribute to algae bloom.
In Austin’s climate, hardy water lilies (as opposed to tropical ones) can be overwintered in the bottom of a 2-foot-deep stock tank. The water lily will die back to mushy stems in the winter, which should be collected and discarded from the pond. Every year in early spring, as new growth begins, divide your water lily and replant in heavy clay soil in a pond pot with no holes in the bottom. Top-dress the pot with pea gravel to keep the soil from floating into the water.
Bird-bathing and insect-drinking platform
With their sheer sides and lack of natural shelves, stock-tank ponds have the advantage of being difficult for raccoons, dogs, and cats (and small children) to get into. But it’s good to make your pond hospitable to birds, insects, and other small creatures that might want a drink or a bathe, or that fall in and need a place to crawl out. I put a stone bathing platform on top of a cement block next to the edge of the tank. It gives birds and insects easy access to the water, and I can enjoy watching them enjoying the pond.
Fish
I will add fish — native gambusia or hardy goldfish are good choices — for color and life in the pond, and for eating mosquito larvae. In fact, I never feed my goldfish, letting them forage instead on mosquito larvae, algae, bugs, and the anacharis at the bottom of the pond. Check with your supplier to find out how many fish your size pond can support. If you don’t want fish, you’ll need to rely on mosquito dunks or bits to keep larvae from hatching in the water. Questions about the water temperature and fish are answered below.
Pumps and filters
A filtered bubbler pump can be a nice addition to your pond, especially if you desire the sound of moving water. But in my experience it isn’t necessary for clear water, mosquito control, or healthy plants. It may, however, be necessary if you keep goldfish and your pond is in full sun and the surface water heats up in the summer. Goldfish prefer cool water, and a pump will help keep the water at a constant temperature by circulating cooler water from the bottom. Gambusia (native mosquito-eating fish), while not as colorful as goldfish, are hardier and will not mind warm pond water; therefore, a pump is not a necessity for them. As far as keeping the water clean and healthy, a filtered pump is not required. What matters is having an adequate amount of underwater plants, surface-shading plants, and not overcrowding your tank with fish.
Will the metal tank cook my fish or plants in summer?
This is the most common question I’m asked about stock-tank ponds from fellow hot-climate gardeners. I’ve had a small, 4-ft-diameter pond in full sun, and a large, 8-ft-diameter pond in part shade, and at no time have I ever observed the plants to suffer in the heat. After all, they’re sitting in a nice, comfy bowl of water. They’re loving summer!
Whether the water will get too warm for fish, however, depends on a number of factors: the size of your tank, how much sun it gets, whether you put a recirculating pump in the pond, and what kind of fish you choose. Goldfish prefer relatively cool water temperatures and need more oxygen as the water temperature increases. Therefore, if you stock your pond with goldfish, consider installing a pump to circulate the water and aerate it. You might also bank soil up on one side of the tank to provide insulation — easily done if your tank is situated in a garden bed rather than free-standing in the open. Alternatively, stock your pond with gambusia, native mosquito-eating fish, as they tolerate warmer water than goldfish. You can usually find both types of fish at pet stores or pond-supply stores.
Will the galvanized coating on the tank poison my fish?
I get asked this at least two or three times a month. I can only answer from my own experience: no, I’ve never noticed any problems with goldfish or gambusia (mosquitofish) dying off when placed in a galvanized tank. And I’ve seen many tanks in various gardens over the years that contain fish, including at the Wildflower Center. My mom even had one with koi for several years, although they did eventually outgrow that small tank. My advice is to wash out your tank thoroughly before filling it with water, and once you fill it hold off on adding fish for a week or two so the chlorine can evaporate and the water temperature can stabilize.
Maintenance
The only maintenance is netting fallen leaves from time to time, fertilizing once a month during the growing season, mucking out the bottom once a year, and dividing plants once a year. Expect an algae bloom — the pond will turn green — soon after you plant your pond and maybe each spring as the water heats up. But by keeping the pond stocked with oxygenator plants and being patient until the water lilies leaf out to shade the water surface, you’ll find the water clears up on its own without need for any chemicals. Just as nature does it.
This is part 1 of a 3-part pond series:
Part 1 — How to make a container pond in a stock tank
Part 2 — Winterizing a stock tank pond
Part 3 — How to spring clean your stock tank container pond
Update: August 15, 2009. Here is how the pond looks after only a few weeks!
Disclaimer: This post details what has worked for me in making a stock-tank container pond in zone 8b. Gardeners in colder zones may not be able to overwinter pond plants or fish in this way.
All material © 2006-2012 by Pam Penick for Digging. Unauthorized reproduction prohibited.
