What you might need will depend on your soil and the nutrients that soil contains. Plants need a balanced food supply, just as we do, so you add to the soil what the plants need and the only way to know that is with a good, reliable soil test.
Other than "fertilizer" most all plants do much better in a soil well amended with organic matter.

Of all the conifers, junipers are some of the most adaptable as far as soil conditions are concerned. They don't even want much in the way of organic matter -- as long as drainage is good, they should be good to go with little, if any, fertilizing. Like maybe never :-)

Why do you think they may need fertilizing?

Hope you don't mind me butting in Yaron, but I have a question which may help if answered.

I have a Whichita Blue Juniper which - apparently - is a fullproof plant, yet it doesn't grow as well as I would expect. Barely any new growth last year. I've had to remove three Rocket Junipers for 'browning' and lack of new growth... What would be an ideal PH level for these plants?

We have high acidity being in the nor'east. Great for native pines/spruces/rhodies, but what about Junipers? Do they prefer a more alkaline soil?

I spent a couple of hours yesterday doing the google things trying to find an answer to this, but no-go. I'm starting to think this may be the issue.