a growth medium that is capable of supporting plant life includes a water retention component and soil . the water retention component can be a water retaining grain polish , bran or cut , short mineral wool fibers . a method of making the growth medium includes the steps of providing the water retention component and the soil , applying the water retention component to the soil and admixing the water retention component into the soil to distribute the water retention material within the soil to improve the water retaining capabilities of the soil . vegetation matter , especially when mixed with animal excrement , will also contribute to the water retention property of the growth medium in addition to its slow release nutrient .