The graft should not be covered as far as I know. I plant mine shallow enough that you can see the root "legs" at or slightly above the soil line. The graft should be well above the soil.
Tony

The graft line of any grafted plant should never be covered with soil or mulch. This will cause the graft to rot and therefore kill the tree.
Andi

Tony is right -- a properly planted citrus tree will always have one or more roots exposed above the surface of the soil.

Does this include in-ground citrus? I've got Poncirus and Flying dragon growing in the garden. I've been mulching since I'm in IL..we have freezing winters..so far, w/one flying dragon, I've mulched yrly..the other two were planted this spring. Should I not mulch? I thought the mulch would help protect from winter winds..NO? Toni

Toni,
FD and other Poncirus are a special case. Yes, we still plant them high, but one of the major reasons for that is to avoid foot rot caused by Phytophthora, and pure Poncirus is virtually completely resistant to it. So mulching may be ok for you. We don't mulch any citrus here, because of the Phytophthora danger.
Malcolm

Malcome, now you've got me worried..I hope I didn't plant the FD and Poncirus too deep earlier this spring..(S) I'll have to check it so it's not too deep.
Because I'm in IL and it gets so cold, Ihave to add some type of mulch to prevent those freezing winter days..if only we lived somewhere warm..(SIGH) Maybe one day. Then I won't have to worry about mulching..Thanks,Toni