CSLB C-27 Landscaping ContractorSite Preparation and DrainageEasy
A landscape contractor is planning a new planting bed on a site with heavy clay soil and poor drainage. To improve the soil structure and aeration for plant health, which of the following organic amendments would be most effective?
- AComposted organic matter
- BGypsum
- CLime
- DSand
Show answer & explanationAnswer & explanation
Correct answer: A. Composted organic matter
Composted organic matter is highly effective in improving the structure of heavy clay soils by creating aggregation, which increases aeration and drainage while also enhancing water retention and nutrient availability. Sand alone can worsen clay compaction, and lime/gypsum address pH or sodium issues, not primarily structure.
Why the other options are wrong
- B. Gypsum (calcium sulfate) is used to improve highly sodic (high sodium) clay soils, but it's not the primary amendment for general structural improvement in non-sodic clay.
- C. Lime is primarily used to raise soil pH (make it less acidic) and does not directly improve the physical structure of clay soil.
- D. Adding sand to clay soil without significant organic matter can create a concrete-like mixture, worsening compaction.
Organic Matter for Clay Soil
Incorporating organic matter like compost into heavy clay soil improves its structure, aeration, drainage, and water-holding capacity.
- Breaks up dense clay particles, creating aggregates.
- Increases pore space for air and water movement.
- Enhances biological activity and nutrient availability.
- Improves workability of the soil.
Memory trick: Clay needs a Compost Hug to breathe and grow.