Try taking the plants indoor to see if that helps, it may be the
environment rain water ?

Find the plants you have and find their individual care needs. It might
help to group them to similar care. Each plant has different care
needs. Some need to be watered weekly while others need less. Some
plants need drainage and too much water will make fungus grow and
attract parasites.

Go to http://plantcare.com/ and find your plants.
There are great tips at http://forums.gardenweb.com/forums/