Weeds in my pond in Uxbridge, Ontario

(Question)

Hello,
I have a weed growing in my pond in Uxbridge, Ontario.
I have had some taken out but they still grow.
Is there any way to get rid of them?

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(Answer)

Thank you for contacting the Toronto Master Gardeners with your gardening inquiry.

Trying to identify a plant from a photo is very difficult. We usually require a clear close up image of the leaves and flower in order to make a positive ID. From what I can see from your photo your weed in question could be Elodea canadensis, Canadian Pondweed. This weed grows rapidly in favourable conditions.

Elodea is a rooted multi-branched perennial plant that grows from stolons ( creeping stems) and can survive and grow as floating fragments.

Aquatic weeds are usually a problem during the warmer months of the year when water temperatures rise above 6°C . This summer we have had a record number of days where we saw temperatures rise above 30C resulting  an increase in the number of weeds.

In Ontario under the Pesticide Act there are no herbicides approved for the control of aquatic weeds in home gardens. Removal of this noxious weed requires vigilance and patience.  Elodea can be removed by raking it from the pond making sure to remove all the fragments since this plant will reestablish from any remaining fragments. Covering the plants to block light with an algal bloom may result in its eradication. You might also try lowering the water level before the winter. The success of this method is related to the degree of desiccation, air temperature (at best freezing conditions after drainage), and the presence of snow. The cold temperature will freeze and kill the roots of this plant.

Here is some additional information on this plant. You may also find this article of interest.

Finally, you may also wish to read one of our earlier posts titled  Winterizing Garden Water Features (Pond) which lists a number of resources on how to prepare your pond for winter along with articles on algae control.

Good Luck!