Mary Ann, ok, a different angle. It again though matters about your soil...if you have really bad soil, some times it's best to double dig and build up the soil with admendments and build a nice big bed to plant your hydrangeas and other plants in. When doing that I like to use a top grade soil mulch made of manure, soil, granite sand and bark that has been well turned and aged. We have a great local provider for that. If I didn't have that, in the past I've used mushroom compost, top soil, aged pine bark and mixed that with the native soil.
Now, if you have decent soil and are spot planting, what I do is to mix in some fresh mushroom compost (1/2 a bag) with a hand full of milorganite fertilizer (all organic) - mix that with the native soil well and then plant with the crown just above the soil line.
Hope that helps...I use Milorganite for just about all my fertilizing by the way.
Mary Ann, any decent garden center carries it.
If you have a well draining loamy top soil you can plant your shrub right in it. When you put a lot of amendments into a hole you dug the roots will tend to stay there and not venture outside where "the picking is less good". That is why such practice is generally discouraged by arborists when planting trees an shrubs. If the soil in the site you chose is very poor you will have a lot greater challenge to improve a whole bed first so it has nutrients and good drainage or perhaps opt for a better location.
Soil's Ph plays a role in the color of flowers (see Do's and Don'ts forum) but find out first what yours is. You might like the color you get naturally (without alterations) and only apply Ph neutral fertilizers in the future. Enjoy you new plants!
I guess I've been very lucky, as I dig a hole (I have rock-hard clay soil, except in the winter when it actually looks & feels like real clay), add about half a hole-full of whatever potting mix I've got on hand mixed with a little of the natural soil, plant the hydrangea and see what happens! I never feed them or anything. I haven't had one die on me yet, altho they do wilt if there's too much heat. The other thing I've found, and clearly it has to do with the soil, is my plant colors change from year to year, plant to plant, and some plants have pink, purple and blue all on the same bush! It's always a surprise in my yard. :) Part of the fun!