Jade plants need full sun in order to grow properly and need to be drained well. Allow the soil to dry out completely before each watering. Softening leaves indicate time for more water. cast iron plants can handle low light, extreme temperatures
One of the fundamental principles of organic gardening is to "feed the soil, not the plant." The idea behind this concept is that if you start with healthy soil in the first place, you won't need a lot of additional fertilizers.