Potting the plants is always a good idea for the first year so make sure there are not piggy back unwanted plants growing in the pot or pans. After the first year you can transplant the plants directly into the pond. If the lily varieties are truly dwarf versions they will not grow deeper than 4ft and spread slowly the next 10 years. Larger variteties will spread deeper that 3-4ft depending on variety. Hybrid lilies are easily controlled with the correct aquatic herbicide.

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America's Journal of Pond Management