NOT A TEACHER
Here's the stuff taken from my Longman Pronunciation Dictionary.
-ed, -d /t, d, ɪd əd/ - This unstressed ending has three regular pronunciations:
1. After t or d it is pronounced ɪd or, less commonly in British English but regularly in American English, əd, as hated ˈheɪt ɪd AmE ˈheɪt̬ əd, needed ˈniːd ɪd AmE -əd.
(In singing, exceptionally, a strong-vowelled variant ed is usual, as ˈniːd ed.)
2. After the other VOICED consonants or a vowel sound, it is pronounced d, as called kɔːld, seemed siːmd, vowed vaʊd, tied taɪd, feared fɪəd AmE fɪ[SUP]ə[/SUP]rd.
3. After the other VOICELESS consonants ( p, k, tʃ, f, θ, s, ʃ), it is pronounced t, as gripped ɡrɪpt, patched pætʃt, knifed naɪft.
Certain adjectives have ɪd, əd against these rules, as wicked ˈwɪk ɪd, -əd. The same applies also to most words in -edly, -edness as markedly ˈmɑːk ɪd li, -əd- AmE ˈmɑːrk əd li. This 'syllabic' pronunciation of the ending formerly applied to all -ed formations, and is still heard when people recite older literature, where it may be required for scansion purposes: thus (only in imitated old pronunciation) seemed ˈsiːm ɪd.
I hope it helps.
