Just put the Giants where you think they are going to stay. You don't want to be moving them later on when they're fully growed. Other than that, put things where you like them. You could do themes or families (all halcyon types), but there is no right or wrong, just what appeals to your eye.

Steve

as the giants ....

go to the library.. go to myhosta .. and find mature size.. in width.. then add 2 feet ...

so if it says 4 feet wide.. give it 6 feet ...

which would mean.. if you were putting two next to each other.. i am talking a minimum of 6 feet apart ...

ergo.. as paul notes.. fill in the blank space.. with some that can be moved .. when the monster starts to get really big ...

ken

That's a huge garden, so some things to think about--

-wide enough paths for easy access (walking, grooming, maintenance, cart or wheelbarrow of mulch, etc.)
-irrigation
-seating
-adding lots of organic matter before planting, so they'll take off
-repetition
-focal points whether color spots or hardscape

I agree about the paths. Once hostas are about 10 feet away from the path, it's hard to see what they are and their specific traits. My garden is over 100 linear feet and in the areas that are deeper than 10 feet, people always tell me I need a path.

Start with the backbone of the garden.... the paths and the boulders. These are hard/nearly impossible to add after the fact.

Also think about the architecture of the garden... the bones.... trees, larger shrubs, garden art, pergola/arbor/trellis/obelisk/fencing kinds of things. A sea of hosta needs to be "interrupted" by something. It'll give the eye a chance to rest.

That's all I can think of right now.

Thank you all! Absolutely exceptional advice! With the garden I have now I have noticed that I already have a "sea of hostas" effect. I have not been as good as I should with regards to labeling my hostas. I do know that, according to Hostalibrary", I have at least two giants, and a bunch of hostas that will be 6' wide at maturity. Thank you for the advice to check "myhosta". I have not been able to access the site yet as their bandwidth has been exceeded.