Answer: Humus is a term often used interchangeably with compost. It is the almost completely decomposed organic matter that is rich, dark and sweet smelling, like the layer of dark soil beneath the leaves in the forest. Definately add plenty of organic matter to your soil. Compost is terrific stuff! It adds organic matter to the soil, improves drainage in clay soils, improves water and fertilizer retention in sandy soils, provides nutrients, increases soil microbial activity, and encourages earthworms. I like to incorporate compost into the soil before planting, but I also use it as a mulch or top dressing. It will act as a great mulch/top dressing for your existing flowers and over time break down and improve your soil. As it ages, some of the nutrients in compost will leach away, but compost is generally not extremely high in nutrients anyway. It will still provide many benefits for your soil no matter when you use it. You can also add top soil, but it may be more expensive than compost. It's a good idea to loosen the soil to a depth of at least 12 inches and 18 is better to assure there is good drainage and roots can easily penetrate.
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