Answer: Most daisies and other flowering perennials including dianthus do best if you remove the spent flowers and stems promptly during the growing season. In spring, gently clear away any left over debris so the crowns don't smother. They also appreciate a light mulch all season and a top dressing of compost each year. Some gardeners will also give them fertilizer but how much and what kind would depend on the results of some basic soil tests.
In general these are both easy care plants. However, daisies prefer a rich moist yet well drained soil (meaning not soggy) in full sun or part shade while dianthus prefer a very well drained, lean, neutral to alkaline soil in full sun. The daisies seem to do better if divided every other year or at least every third year. Dianthus can be divided about every third year to rejuvenate the plants, or you can simply start new replacement plants from cuttings when the originals begin to look shabby. If you are looking for more detailed information about perennial gardening you might take a look at some basic books. One I particularly like is "Perennials for Dummies" by Marcia Tatroe, ISBN 0-7645-5030-6.
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