hey man. You can definately use the same dirt over but you have to consider all the variables of this move. The dirt has been fertilized over & over so all the left over nutes may mix witthe soil in a way that will cause nute burn to any young plants. The dirt also may have lost tons of natural vitamins that you may not be able to feed on your own. All the micronutrs such as iron or magnesium calcium. So it's best to just throw the dirt outside & start over wit fresh dirt.