I've some evergreen bushes, some arbor vitaes, hydrangias, and a few other foundation plants that I'd like to fertilize. Would 10-10-10 be ok to use? Better now than late fall? Garden stores have special formulas for each kind of plant and it would seem a balanced formula would generally do ok with most established plants but thought I'd put the question out there for comments.
Why? Just a little more information please. Where are you? How old are they? Any particular problems such as don't bloom, etc.? Just maintenance feeding?
it would seem a balanced formula would generally do ok with most established plants
Generally speaking you are correct. If I understand correctly from your comment that these are established plants, with no problems, then a very light application of a triple 8 or 10 would be fine. I would cut back on the nitrogen since you do NOT want new growth going into the winter. Some resources suggest that a little extra potassium (the K in NPK) helps in late fall and you will notice that in the "winterizer" formulas out there. The idea is to help with moisture at the cellular level but that's another thread.
Personally, I would use a light application of maybe a Nursery Special 6-12-12 or even a cheap 5-10-15 if you can find it at a garden center. Comparing those two- 6 is close to 5 on the N and 12-12 splits the difference between the 10-15.
Or, just go into winter well-watered, wait for spring, and fix 'em some breakfast.
If it's worth doing, it's worth doing right. If you wouldn't put your name on it, it ain't done right!
Near Philadelphia so we get a fairly hard winter.
I'll look for something with a lower N level.
This is just to give them a bit of food since the soil is clay with little humus/organic matter for food.