What is a notable requirement for using bark as a substrate?

Using bark as a substrate has specific requirements to ensure optimal growth conditions for plants. One notable requirement is that it must be composted for at least 30 days. Composting helps to break down the bark materials, making them more suitable for horticultural use. This process enhances the physical structure of the substrate, improves aeration and drainage, and reduces potential phytotoxicity—substances in the raw bark that could harm plant growth.

Additionally, composting helps to create a more balanced nutrient profile, which is crucial for plant health. It also reduces the carbon-to-nitrogen ratio, promoting better microbial activity needed for healthy plant growth. Therefore, ensuring that the bark has been properly composted is essential for its effectiveness as a substrate in greenhouse management.

The other options discuss properties or uses of bark that are not focal requirements. While mixing with sand can enhance drainage, it is not a necessary requirement. Rapid decomposition could lead to issues with substrate longevity, and high nitrogen content is not typically a characteristic of bark, which tends to be lower in nitrogen compared to other organic materials. Thus, the necessity for composting for at least 30 days stands out as a critical requirement for using bark as a substrate effectively.