Answer: You need to wait as long as possible for the foliage to grow and wither and refuel the bulbs. It is best if you can wait until it has fully faded before you remove it but this can easily take over a month. At a minimum try to leave it until it is at least half way brown. Usually it is possible to plant transplants or seedlings in between the bulbs and allow the daffodil foliage to flop over and then be concealed by the annuals as they grow. Alternatively it can sometimes work better to plant the daffodils at the rear of the bed and plant the annuals to the front.
Some of my favorite yellow flowered annuals for sun are melampodium, zinnia linnearis and of course yellow marigolds look terrific with the blue flowers. These all like hot weather and should bloom all summer and into the fall.
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