Answer: It's best to wait until the bulb foliage dies down on its own before removing it. The leaves are providing energy to the bulb for next spring's flower. After the foliages withers away you can cut it off at soil level. You can plant perennials in the same bed with the bulbs, but don't position the root masses directly over the bulbs - they might have a hard time sending foliage up through the root mass. If you accidentally dig up a bulb - or if you have to reposition them as you're planting your perennials, it shouldn't be too tramatic for the bulbs. Just replant immediately - before the roots have a chance to dry out.
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