well, i wouldn't have used a bigger pot, but the new soil was good. also, you know, diffenbachias can be cut off and the base will send new shoots and the top will root if you just plop it into the soil beside the mother plant. just be careful, the sap is irritating to some.

In very simple terms... When you set a cutting in water, the water will always be in motion as it heats and rises to the top. During that movement it is picking up fresh oxygen before it circulates back to the bottom of the pool. Waterlogged, soggy soil is too dense for that process to be quick enough to move the oxygen and CO2 to the roots and the plant basically will suffocate.

Be sure to heed Jiffy's warning regarding the sap. I can be very toxic in some cases. The common name "Dumbcane" comes from medieval times when the master (or Lady) of the manor would make the sevants chew a leaf to ensure their silence about certain "no nos" they may have witnessed.
The Dumbcane would cause the servants tongue to swell to a point that they were incapable of speach.... insuring their silence....

Or so the legend goes...

Beware of the sap, just to be safe! OK?

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Thanks Bill, Sorathien.

The story behind the 'dumb cane' seems pretty insightful and interesting!

Thanks for the tips guys.