Grow bags generally support a good irrigation system in ensuring your plants get the right amount of water needed. Sadly, they drain out water three times as fast as the traditional pots. One way to keep your grow bag from drying out is by watering it as frequently as possible by starting with an early morning daily routine.
Another option would be to mulch the top of the grow bags with either barks or rocks to reduce the rate of evaporation from exposure to sunlight. Also, you can learn to water your plant deeply to get long-lasting watering results without having to over-water. Do not be afraid to soak plant grow bags with water to ensure they water beyond the top layers.