Lorn, you have enough seedlings coming to fill an acre Field! (Or more!)
Brian, I too think your seedlings a coming along very nicely... better than some of mine, in fact. I started using gravel over seeded pots more than a decade ago with alpine materials. Many of these are best seeded uncovered, except by a layer of pebbles, or are seeded
after the layer of gravel is placed. It didn't take me long to realize the extra values that gravel provides:
--- temperature moderation
--- moisture moderation of underlying medium
--- perfect drainage
--- sterile conditions
--- major nutrient (NPK) absence - important for dryland, alpine and desert plants
--- permanence (no biodegradation)
--- sunblocking (prevents growth of algaes, mosses and liverworts)
The last two have proved very helpful with pots that are slow to develop or when seeds don't sprout for another year or two. I use chicken grit (usually #2 size) on just about everything now, even woodland species. Different parts of the country have the same thing but made of different materials. I have our native granite. I used this pic for an article and presentation for our Rock Garden Society:
