Certified Professional Horticulturist (CPH) Practice Exam

Heavy soils, often characterized by a high clay content, can hold nutrients and moisture well but tend to have poor drainage and aeration. Adding organic matter, such as compost or well-rotted leaves, is beneficial for several reasons.

First, organic matter helps to break up the compacted texture of heavy soils, improving their structure and promoting better aeration. The addition of organic material increases the soil's porosity, allowing for improved movement of air and water, which is essential for healthy root development.

Secondly, organic matter enriches the soil by supplying a diverse range of nutrients as it decomposes, stimulating microbial activity and further enhancing soil fertility. This biological activity also contributes to the creation of aggregates, which helps to mitigate the negative impacts of heavy soils.

While fertilizers provide essential nutrients, they do not improve soil structure. Adding sand might seem like a solution to improve drainage; however, it can lead to a cement-like mixture when added inappropriately, exacerbating compaction issues. Mulch primarily serves as a protective layer on the soil surface and does not address the underlying issues related to heavy soils.

Thus, enriching heavy soils with organic matter is the most effective approach to improve their overall condition and functionality in a garden or landscape setting.