According to John: Container Gardening
Our John & Bob’s GrowGreen Smart Soil Solution System is tremendous for container gardening of all types because of the container’s tendency to quickly leach out nutrients. Obviously, good drainage is imperative in container gardening, but it does create the problem of empty, lifeless soil. Topical applications of PENETRATE, OPTIMIZE, MAXIMIZE and NOURISH, every 6 months, will keep the soil lively and nutrient-rich. It will also improve the moisture retention capability of the soil while maintaining the soil’s lightness and ability to drain. Our system also negates the need to continually change the soil. Year to year, you can just top off soil levels, rather than having to completely replace all the soil in a container.
A pet-peeve of mine is the continuance of the mistaken belief that putting a layer of gravel in the bottom of a container will improve the drainage and is a good idea. It will make the drainage worse and is a bad idea. It is much better to use all good quality potting soil and no gravel. The gravel (or any other material with a different consistency) meeting the soil creates an interface. Because of the interface, the soil has to become completely saturated before it will drain into the gravel and out of the pot. If you need something over the hole in the pot, use a paper coffee filter, a piece of screen or a shard of pottery. Don’t create interfaces in containers or anywhere in your garden soil. By heeding this you will maximize the effective exchange of air and water--- a real key to successful gardening.