Which substrate has poor water retention but good aeration and drainage?

Sand is known for its properties that allow for excellent drainage and aeration due to its large particle size and low ability to retain moisture. When used in horticultural contexts, sand creates a structure that prevents compacting, leading to good airflow around plant roots. This quality is crucial for preventing root rot and promoting healthy plant growth, as roots require oxygen as well as water.

In contrast, other substrates such as pine bark and sawdust tend to have better water retention capabilities, which can sometimes lead to over-saturation in certain conditions. Perlite, while also providing good aeration, retains some moisture due to its porous nature, but not to the extent of organic materials like pine bark or sawdust. Thus, the combination of poor water retention, great aeration, and effective drainage makes sand the correct choice for this question.