I have several ivies, nephthytis (sp?), a diffenbachia and a spathiphylum growing happily in water filled vases. I have never fertilized them. Is there anything I should be adding to the water other than a bit of vinegar?

As long as they are doing well, I would not do anything different. "If it is not broke, do not fix it" is a quote (variation) that comes to mind.

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Nadine Bielling
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Gardener Exchange Forum

The Laws of Ecology:
"All things are interconnected. Everything goes somewhere. There's no such thing as a free lunch. Nature bats last." --Ernest Callenbach