A good substrate is essential in order to achieve strong and healthy plant growth. There are a huge variety currently available as manufacturers have realised the importance of a planted aquarium substrate. Some key factors to remember are the two different types - Complete (meaning you need nothing more) and one's that need topping with a gravel. Both have advantages and disadvantages, and it's really a case of deciding which suits your aquascape and your budget. Some will also effect your PH which can be advantageous for plant growth and pH.