Green plants require sunlight in order to create their own food through photosynthesis. Without access to sunlight, plants are not able to grow in a cave. Caves are usually dark and filled with air that has very little carbon dioxide, which is an essential ingredient for the photosynthesis process. Additionally, the soil found inside caves is usually not suitable for plant growth due to the lack of nutrients. Without the right environment, essential nutrients and sunlight, green plants cannot thrive in a cave.