Certified Professional Horticulturist (CPH) Practice Exam

What type of mulch helps retain moisture and improve soil temperature?

1. Plastic mulch

2. Bark mulch

3. Gravel mulch

4. Rubber mulch

The correct answer is: Bark mulch

Bark mulch is an effective choice for helping to retain moisture and improve soil temperature. When applied around plants, it creates a layer that slows down evaporation from the soil surface, thereby keeping the soil moist for longer periods. This is especially beneficial in areas with hot weather, as it helps maintain a more stable soil temperature, which can promote healthy root growth and overall plant vitality. Additionally, bark mulch provides a natural material that allows water to penetrate while still providing insulation. It decomposes slowly, adding organic matter to the soil over time, which can further enhance moisture retention and improve soil structure. In contrast, plastic mulch can effectively retain moisture but risks overheating the soil, potentially stressing plants. Gravel mulch does not retain moisture well, as it allows water to drain away too quickly, leading to drier soil conditions. Rubber mulch, while it provides some insulation and can suppress weeds, does not contribute to soil health or moisture retention like bark mulch does. Therefore, bark mulch stands out as the ideal option for improving moisture retention and regulating soil temperature.