Phosphorus is most crucial when:

Phosphorus plays a vital role in the establishment of new stands of turf because it is essential for root development and overall plant vigor during the early growth stages. This nutrient contributes to the formation of DNA, RNA, and ATP (adenosine triphosphate), which are crucial for energy transfer and metabolic processes in plants. When new turf is being established, a strong and extensive root system is necessary to support the plant's above-ground growth as it becomes acclimated to its environment.

In contrast, while phosphorus does contribute to maintaining existing plant health, its primary importance is during the establishment phase, where it enhances root growth and promotes a strong foundation for future development. In pest control, phosphorus does not have a direct role, as its function is largely focused on plant growth and development rather than on managing pests. Lastly, improving soil structure typically involves different nutrients and organic matter, rather than the phosphorus that directly influences root systems and early growth.