What characteristic reduces the drainage of soil in greenhouses?

The characteristic that reduces the drainage of soil in greenhouses is high bulk density. When soil has high bulk density, it means that the soil particles are tightly packed together, leading to less pore space for air and water. This tight packing restricts the movement of water through the soil, resulting in poorer drainage. Good drainage is essential for healthy plant growth, as it helps to prevent waterlogging and root rot.

In contrast, high pore space, which allows for better drainage, is beneficial for plant health. High nutrient content is important for providing the necessary elements for plant growth, but it does not directly influence drainage capabilities. Low water holding capacity signifies that the soil doesn't retain much moisture, which usually helps with drainage rather than hindering it.