| Over the past 2-3 years I have been observing the instances of hydrophobic soils and trying to make a connection. In a very large proportion of cases I have noticed that the landscape soil mixes are involved. If you have ever looked closely at these they contain a great deal of organic matter, a small amount of sand but very little or no clay. The sand particles become coated in a layer of fine organic matter which renders them water repellent once they dry out. Detergents and all that will no doubt alleviate the situation temporarilly but if you really want to solve the problem then you must permanently increase the clay content of your soil. Clay particles are very hydrophillic or water loving, are very minute and will eventually penetrate and disrupt the coating of organic matter over the sand particles. I always use granitic sand as a top soil and I never have problems with it becoming water repellent, even when it is bone dry. So you can either mix your top soil with granitic sand or you can use a product called Volclay Bentonite. This is pure refined clay that is used a clarifying agent by the wine industry and by farmers to seal leaks in their dams. It comes in 20kg bags and can be rotary hoed into your top soil in much the same way as gypsum. It is not a partucularly easy product to find however I know of one source in Melbourne and will get it in for people if they wish to try it. | 
