CSLB C-27 Landscaping ContractorSite Preparation and DrainageMedium
A C-27 contractor is preparing a planting bed on a site with poor drainage and heavy clay soil. To improve both drainage and soil structure for healthy plant growth, which soil amendment should be incorporated into the top 6-8 inches of the existing soil?
- ALimestone
- BPerlite
- CGypsum
- DComposted organic matter
Show answer & explanationAnswer & explanation
Correct answer: D. Composted organic matter
Composted organic matter significantly improves heavy clay soil by creating aggregates, which leads to better soil structure, increased aeration, and improved drainage. It also enhances water retention in sandy soils and provides nutrients, making it a versatile and highly effective amendment.
Why the other options are wrong
- A. Limestone is used to raise soil pH and provide calcium/magnesium, but it does not directly improve soil structure or drainage in clay soils.
- B. Perlite improves aeration and drainage but offers no nutritional value and is generally used for potting mixes, not large-scale landscape beds.
- C. Gypsum can help flocculate (clump) clay particles in sodic soils, but it doesn't provide the long-term structural improvement or nutrient benefits of organic matter for general poor drainage.
Clay Soil Structure Improvement
Methods and amendments used to enhance the physical properties of heavy clay soils, specifically to improve drainage, aeration, and workability.
- Clay soils have small pore spaces, leading to poor drainage.
- Organic matter creates aggregates, improving structure.
- Better structure allows for healthier root growth.
Memory trick: Clay so tight, needs compost's light, to drain and breathe, and plant's relief.