There are many different materials available for use as the substrate in a planted tank, and many different views of the best combination. I'd like to introduce you to some methods that work well on a repeatable and sustainable basis.
Some people are able to grow plants successfully using less than optimum substrate.
In these cases, I believe that the other parameters involved with plant growth are being well met, compensating for inadequacies in the area of substrate. For some reason, aquarists who take excellent care of their fish, and expect the fish to live for several years, are willing to believe that they've gotten their money's worth if they can keep a plant alive for six months. While some plants are certainly more difficult than others, I believe that our goal in aquatic horticulture should be to create an environment where new plants of a species are propagated faster than the oldest die off. The other group of doubters will be those hard core undergravel filter users who feel that a tank cannot be healthy without. To these people all I can say is that in a tank containing a good growth of healthy plants, even a fine substrate will not compact, and it will not become anaerobic.