The number of plants you can grow in a 15-gallon grow bag depends on several factors such as the size of the plants, the species, and their growth habits.
For vegetables and herbs, you can typically grow 1 to 2 plants per 15-gallon bag. For example, you could grow 2 tomato plants, or 1 pepper plant and 1 eggplant.
For flowers, you can plant several smaller plants or a few larger ones, depending on the size of the flowers and how much space they need to grow.
It's important to follow the recommended spacing guidelines for each plant species and ensure that they have enough room to grow and receive adequate sunlight and water. Overcrowding the grow bag can lead to competition for resources and reduced plant growth and health.