Pond Weed Management

Herbicides Don’t Work!

Dear Froggie,

I know you love the weeds.  Native pond weeds although unsightly are wonderful.  They provide habitat for many of the pond inhabitants.  However, they do get out of control.

There are basically two kinds of weeds, the natives and invaders.  Both require the same treatment: replacement.  You want to eradicate invaders and control natives.  You cannot kill weeds with herbicides.  Weeds are survivors using several strategies, e.g. prolific seeds, rhizome roots, and resin coated leaves.  If you kill the weeds, they often return or the nutrients they release will give you another algae bloom or another weed.  This is known as the “herbicide treadmill”.  Further, killing doesn’t lead to health, growing health does.  So don’t use your treasure to kill; buy plants and flowers.

To remove weeds you need to limit the reason they are there.  There are two forms of nutrients entering the pond: sun light and chemical energy. Never fertilize near or above a pond.  If you provide shade, you cool the water and at the same time remove the nutrients from the pond.  For immediate results you can use barley, bacteria and aeration.  This lifts the stored fertilizer gasses from the bottom of the pond.  Because this is not a permanent solution, in all instances, you must plant an equivalent amount of biomass on the shore as there is in the pond.  One third of the sun light is reflected from water.  If you plant shore waterplants, they will have access to all of the sunlight and therefore out-compete the plants in the water.

The willow (Salix) and slough sedge (Carex obnupta) are great replacement plants.  Willow can often become over-prolific.  Slough sedge usually stays in place.  Remember; use these plants in in-flowing streams and seeps into the pond as they are the most common sources of nutrients.  Plants like the invader canary reed grass and blackberry are good indicators of where replacement plants are needed.  Remember, trees such as poplar and alder remove more nutrients than a puny little blade of grass.  Use this power!

Froggie, the idea is to not get rid of your native weeds just limit them and to eradicate foreign invaders.  And further you will get a more robust ecology when the appropriate shore plants are introduced.  Slowly over a couple years watching where you put fertilizer and blocking it will eliminate weeds.

PonDoc             from the pond





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