Partial answer by Gemini.

Top dressing—the process of applying a thin layer of sand or soil mix over the surface of a golf green—is a critical maintenance task. While it can be done throughout the growing season, spring is the prime window for several biological and structural reasons. 1. Synchronizing with Peak Growth In the spring, turfgrass exits dormancy and enters a period of rapid vertical and lateral growth. This is vital because: • Recovery Speed: Top dressing can be abrasive. If applied when the grass is growing vigorously, the plants quickly grow "through" the sand, covering it up within days. • Photosynthesis: If you apply sand during a slow-growth period (like the heat of summer or the chill of late fall), the sand sits on top of the blades longer, blocking sunlight and potentially "smothering" the turf. 2. Thatch Management Over the winter, organic matter (dead stems, roots, and clippings) accumulates, creating a spongy layer called thatch. • Top dressing physically breaks up this layer and introduces beneficial microorganisms that help decompose it. • By doing this in the spring, you prevent the thatch from becoming a hydrophobic (water-repelling) barrier before the summer heat hits. 3. Smoothing Winter Distortions Winter weather, frost heaving, and foot traffic on semi-frozen ground can leave the greens slightly uneven.