Dieffenbachia, also known as dumb cane, prefers soil that's evenly moist but not waterlogged. Here's a detailed guide on how to water a Dieffenbachia:

1. Water when the top inch of soil feels dry to the touch. Use your finger to test the soil moisture level by sticking it into the soil up to the first knuckle. If the top inch of soil feels dry to the touch, it's time to water the plant.

2. Water thoroughly. When watering, ensure that the soil is evenly moist but not waterlogged. Water the plant until water flows out of the drainage holes at the bottom of the pot, then discard any excess water.

3. Allow the soil to drain. Ensure that the pot has adequate drainage holes to prevent waterlogging. After watering, allow the soil to drain completely and discard any excess water that collects in the saucer.

4. Avoid letting the plant sit in standing water. Dieffenbachia is susceptible to root rot, which can be caused by overwatering and letting the plant sit in standing water. To prevent this, always discard any excess water that collects in the saucer.

5. Adjust watering frequency based on environmental conditions. Environmental factors such as temperature and humidity can affect how often you need to water your Dieffenbachia. During the growing season (spring and summer), you may need to water more frequently, while during the dormant season (fall and winter), you may need to water less often.

In summary, to water a Dieffenbachia, wait until the top inch of soil feels dry to the touch, water the plant thoroughly, and allow the soil to drain completely. Adjust the watering frequency based on environmental conditions and avoid letting the plant sit in standing water to prevent root rot.