There appears to be no
sign of a pathogen on the plant. It is probably related to a cultural problem,
over watering, temperature extremes, etc. Make sure that you allow the plant to
dry out some in between watering. How close to the window is the plant--it could
be getting cold damage if it in close proximity to the window. Cut off the
affected leaves and see how the plant does in the next couple of months. If it
continues to get worse, we may need to see the whole plant. As to potting soil
types, there are many good commercial mixes on the market. The main difference
between these and homemade types is the commercial mixes are sterile and usually
light-weight. If you are using garden soil in your mix, you can bring insect and
disease problems indoors, and they are usually a lot heavier.
I have enclosed leaves
from a couple of my arrowhead plants. Almost all of the leaves on the smaller
plant has these brown spots. They are not only on the edges of the leaves, but
in the middle of a lot of them. My larger plant is now getting these brown
areas. Can this be transferred to other plants in the same room? What is the
problem and what do I need to do regarding this? Also, do you recommend an
overall house plant potting soil? I have always mixed my own, but would consider
buying one mixed if I thought my plants would do well in it.