Fertilize if it seems it needs it. Maybe it does not. If not sure about the pH maybe test for that as well as primary nutrients, so you have some specific idea what you are dealing with.

Only fertilize in the early Spring, with a low-nitrogen fertilizer. I use HollyTone.

Kaitain4;

Thank you for the info. So, I should fertilize this tree only ONCE a year?
Would it be a good idea to fertilize it with Mir-grow liquid fertilizer once a month during the summer time?

If your soil is alkaline then you do want some sort of acidifying fertilizer - the Hollytone is good but there are others. I like the Fox Farms Peace of Mind product that is formulated specifically for JM's.

Skip the MiracleGro. If you select an organic product like the Hollytone or Fox Farms, a single season application is all that is necessary. And any foliar spray on JM's should be avoided - it can damage the foliage. Professional growers in my area tend to avoid much supplemental fertilization at all, preferring to mulch with a good quality compost instead. But if your soils are not of a sufficiently acidic pH, the fertilizer may be a better approach to provide nutrients that may be limited by your soil chemistry.

gardengal;

Thank you once again. I will buy a bag of Hollytone since, I saw it last year at my local nursery.
Can the mulch and compost touch the root crown? (they are out of soil, the nursery that sold it to me said leave some of the root crown above the soil when you plant it and never cover them with mulch, soil or anything).
Is that true that the some of root crown should NOT be covered with anything?
One more thing. When I planted it last Sep. I did not add any compost to the hole. Should I dig the tree up and mix a better soil for it? Or leave it alone?

Thank you,

Navid

Don't dig it up!! And you don't want to amend individual planting holes anyway. Ideally, if amending was necessary to adjust soil pH or increase soil tilth and fertility, that should have been done before planting and to a wide area - as much as the anticipated root spread, if possible. Too late now so fertilize moderately (according to directions) to assist with pH and nutrient levels and then mulch. If you don't have compost, wood chips are fine.

I'm not sure what exactly your nursery was telling you, but the top of the root ball (or the root flare, where the roots begin to spread away from the trunk) is best situated at the existing soil level or slightly above. It does no harm to mulch over this - in fact, it can do a lot of good by shading the roots, conserving soil moisture and retarding weed growth. You just don't want to pile on the mulch too thick nor bring up so that it is touching the trunk.

gardengal;

I won't dig it up, bc I don't want to kill the tree. I will fertilize it good. About 1-2 inches of its root ball is not covered with anything and nothing touching the trees trunk (so, top of the root ball is exposed to environment). I will cover them with mulch as you said (just a little mulch)
Hopefully, I won't kill the tree. I have no exp. with J.P. trees, it would be easier for me, if it was a fig tree.

Thank you for the help.