The Q&A Archives: Garden Ponds

Question: I have a garden pond with a waterfall. It has southwestern exposure. I currently have no plants, fish or snails in the pond but want to. I have a horrific algae problem from late March until November. What can I add to prevent the algae buildup-and allow plants and fish to survive in the pond? No chemical treatments though, we are waterfront on the Chesapeake Bay and don't want to contribute any more contamination to the Bay.

Answer: The best control for algae is to cover about three quarters of the water surface with other plants, such as water lilies, to literally shade it out. Like so many things in nature, there is an element of competition in the planting of a closed system water garden. Early each spring (and when a new pond is filled) there is a rush of algae for a few weeks as the water warms until the surface is covered enough by the other plants and things come into balance again. Starting a new pond can test your patience, but a good planting ratio will solve the problem without any additives. Remember too that both fertilizer and fish wastes serve to feed the plants, including algae, so be sure you have a generous amount of underwater oxygenating plants to compensate for any excess; also be careful not to overstock the pond with fish. You will be able to fertilize individual plants as needed, but if your tap water tends to contain nitrates you may not need to fertilize as much. Finally, floating water hyacinths are very heavy feeders and will help cleanse a pond with an imbalance -- but wait until the water is warm before you add these heat loving plants. With a little trial and error you should be able to conquer the algae. A small amount is, by the way, normal. In a healthy pond you should be able to see your hand down about a foot before the water turns murky.

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