Dieffenbachia problem

Question

New leaves are browning and leaves are getting smaller.

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Answer 1

See this article to identify causes of the browning leaf tips:
https://www.gardeningknowhow.com/plant-problems/environmental/what-causes-brown-edges-on-leaves-of-plant.htm

Small leaves can indicate a nutrient deficiency of nitrogen or zinc, especially if those leaves also turn pale or yellowish. Adding a zinc or nitrogen fertilizer, or organic options like compost, according to the package directions may help:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/zinc-and-plant-growth.htm