Fertilize as described above. Dieffenbachia requires filtered light or a northern exposure. Turn the plant occasionally to keep the growth in balance. Water only when the soil feels dry to the touch, and do not overwater. Provide extra humidity by using a saucer filled with gravel.
Cactus requires rapidly draining sandy soil and bright light.
Overwatering is the most common cause of death for indoor cacti. During the growing period, cactus plants need water no more than once a week, perhaps only every two weeks. Provide indoor cactus with a dormant season by withholding water for three to four months, and the plant may reward your efforts by blooming.