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Eco-Answers from the Pros: Controlling Pond Weeds

Does anyone have a suggestion about controlling floating weeds in my pond (duckweed, etc.)? The problem seems to be excessive nitrates. I have tried mechanical harvesting (weeds return rapidly), and am unwilling to use herbicides as suggested by my local DEP. Is Barley straw only applicable for algae control?

The best control for duckweed is hungry fish – before the surface is covered. An appropriately sized skimmer and pump will also keep it under control, but again starting in the spring before the duckweed explodes. I’m not a big fan of chemicals either, but the only other control is mechanical (as above, or a hand skimmer net) or to starve the critters. Very regular doses of barley straw or barley straw extract will help to reduce the underlying nutrient levels as will any of several biological clarifying blends (MicrobeLift PL, Crystal Clear Pond Clarifier, or Pond Logic Pond Clear/Eco Boost). These are blends of naturally occurring beneficial organisms that will tie up the nutrients to reduce weed growth. A vegetative (“wetland”) filter or zone within the pond is the only effective way to actually remove the nutrients as you repeatedly harvest the excess growth in the filter. It’s an awesome addition to the compost pile or as mulch in the vegetable garden.

     Rip Sokol, Fourth Generation Nursery, Mendon, MA

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