Planting Trees Covering Swamp

What's the exact story? 

The earl must have thought that planting 8 trees on first day itself would cause him to wait for only 10 days. That's totally wrong conclusion.

Though started with 8 trees, on other day number will be doubled only not tripled or increased to x8. Starting with 8 trees is like skipping 3 days (2,4,8) if started with 1 tree.That is only 3 days would be saved. 

In short, with 8 plants, the earl need to wait for 77 days!