Germination length refers to the number of days your crop spends covered after sowing. Typically, the crop is covered with some kind of weight on it to improve germination and early crop growth. At the end of your crop's germination days SeedLeaf will generate the "Uncover" task to prompt you to uncover your crop.

SeedLeaf does not account for a "blackout period", which is when the crop remains covered but with no weight. This should be done manually.