Some blooming water plants will attract dragonflies, lovely to watch and also an effective tool in reducing the mosquito population. Photograph by Denise P. Lett | Dreamstime
No garden is complete without a water feature of some sort. In Memphis, one of the most common additions is an ornamental fish pond. But, as much joy as they bring, a poorly managed pond can bring with it a degree of consternation too.
Every year, usually beginning sometime in June, depending upon weather patterns, I start to hear complaints that a property owner’s pond water has turned green, the previously pleasant garden feature becoming a visual blight on an otherwise serene landscape.
Often compared to “pea soup,” this mess is algae bloom, a sudden increase in the population of algae, which I am told by biologists is the simplest organism on the planet. While there exist some reasonably effective algaecides on the market that claim not to hurt fish or desired plants, I remain skeptical of them. They take time to work, and you still have to clean out the dead algae. Prevention, begun before the problem starts, is better, and the problem, though often not noticed until well into the summer, begins near the end of winter in the Memphis area.
Practice early prevention to prevent unattractive “algae bloom” from taking over your water feature. Photograph by Petraausficirova | Dreamstime
FIRST, if you have not done so already, clean out all leaves and other debris. Decaying organic matter is one source of food. Also, make sure your pump is adequately sized and working correctly to filter out and chew up the smaller organic matter you can’t get out with your hands and a net.
SECOND, keep your bacterial levels high. Use a product like Microbe Lift PL, my favorite, dumping a quart to a gallon or more of the liquid in the pond in early March, depending upon the size of your pond, to jump-start your bacterial colony so that it will be ready to consume your fish’s feces as the fish come out of hibernation and begin to feed and defecate more as the water warms. Follow up by adding one to three ounces of the product each week through the end of fall. Moreover, since the size of your bacterial colony is a function of the surface area upon which it can grow, if you don’t already have a 2- to 3-inch layer of medium-brown gravel, a cheap commodity available at area mulch yards in Memphis, you should add one, being sure to rinse it off thoroughly before adding it to the pond.
THIRD, since your beneficial plants get the sunlight they need through leaves above the water’s surface, lightly tint the water, using a product like Microbe Lift Bioblack, to decrease the amount of sunlight penetrating the surface. Remember, a little goes a long way and once you put it in, if you’ve put too much, it’s hard to undo it. Thus, maybe add one-fourth of the concentrate specified on the package for a pond your size and wait a week before adding another fourth, stopping when it is visibly tinted but not so much so that you cannot see the bottom of the pond.
Choose plants around the edge of your pond that will shade it, such as a small or medium-sized ornamental tree, some Fatsia japonica, or other shrubs. Photograph by Denise P. Lett | Dreamstime
FOURTH, choose plants around the edge of the pond that will arch over the pond and shade it, such as a small or medium-sized ornamental tree, some Fatsia japonica, or other shrubs. If you add a tree, it should be deciduous and placed so that it shields the pond from eastern, southern, or western exposure, with a southwestern exposure being particularly problematic for ornamental ponds.
FINALLY, use water plants to cover at least 50 percent of the pond’s surface. You’ll want to use a combination of plants for deep water, shallow water, and plants that float, as well as a combination of plants that are evergreen, perennial, and annual for our area. In addition to reducing the sunlight that penetrates the water’s surface, water plants provide a place for fish to hide from predators, cool the water, and increase the oxygen level of the water.
A good choice for evergreen — my favorite for ponds, in fact — is Equisetum hyemale, which clumps into slender stalks, providing year-round interest and needing little care. As an added benefit, it attracts dragonflies, lovely to watch and also an effective tool in reducing the mosquito population. You’ll see the dragonflies resting atop the tall reeds and then dive-bombing the water as they spy their prey, which is their food and your enemy.
Other water plants that are favorites of mine when I install a pond, include:
1. Nymphaea;
2. A mix of annual floaters like Pistia stratiotes, Eichhornia crassipes, and Ceratophyllum demersum;
3. Louisiana irises, a group of five species of iris, which tend to grow well in pots in ponds; and,
4. Acorus gramineus.
While I can’t absolutely guarantee that algae bloom won’t happen — Mother Nature can be rather unpredictable — I can say that I’ve never seen a client who carefully followed all of these steps experience an algae bloom. But, you must start now.
John A. Jennings is an ISA Certified Arborist, and manager of horticulture for Palladio Garden in Midtown Memphis.
