will grass clippings and dead cedar needles work ok as a mulch in my flower beds and garden?

will i have to till them in in the spring, or will perenials grow thru them? will they work ok in the garden also? i have mostly cedar droppings, as my trees are shedding a bunch. also, are there 2 different types of cedar trees? i ve never had a cedar tree that lost this many needles……….

Tillie