Regardless of the N-P-K analysis of a fertilizer, one usually adds 1 tablespoon to a gallon of water. BECAUSE: a gallon is the standard used for the analysis. . . .i.e. how much would one have to add to a gallon of water in order to get that analysis? The concentrated amount to add is almost always 1 tablespoon.
It's easier to make up a whole gallon, to get that N-P-K analysis and then use some portion. To make 1/2 gallon and get the same N-P-K, one would have to do some calculating and 1/2 gallon of half strength (whatever fertilizer) requires even MORE math (math! ptooey ptooey!!).
Seed starting relies heavily on propagation spreadsheets: what to do, when and how . . . .based on experience of many, many gardeners and many, many years And fertilizers require some common sense. Whatever fertilizer and strength one uses on the same variety of mature plant, is usually the one that should be used in seed starting process. Not all seedlings are to be fertilized beginning at the same stage or with the same fertilizer or with the same dilution. For instance, MG Tomato is used on mature tomatoes and the directions ON THE BOX says to use half strength for seedlings . . and a propagation spreadsheet reccomends beginning at 2 sets of true leaves. In contrast, MG Bloom Booster is often used for flowers and a propagation spreadsheet reccommends 1/2 strength beginning at the 2 sets of true leaves stage for zinnias. . . but for marigolds, it's 1/4 strength at the 3-4 sets of true leaves stage (I surmise this is because mature marigolds get 1/2 strength.)
