I just got a nice sized dieffenbachia. After transferring it to a nice pot it has been suffering. I gave it plenty of water, more soil, and a pot not too big for the plant. It did get subjected to cold for about 20 mins. Now almost half of the leaves are black and most of those black leaves are now crisp. Should I trim off the black leaves and leave the healthy ones? Or should I trim it all the way back to the stems?
It sounds as if your plant actually froze. Yes, cut off any dead, black, grayed, crispy material. It is worthless to the plant.
Please send a picture, let us know where this plant lives; indoors, what window orientation (west, south, north or east), love to see how much is still alive and able to make food for the plant.
What kind of soil did you use? Garden soil or sterilized potting medium? Did you put rocks or gravel beneath the soil for supposedly enhancing drainage? What is your watering method? Fertilizer? Where on this planet do you live?
Do you have cats or dogs in your family? This plant is very toxic to pets! Oh, and kiddos.