Answer: In my experience, they should be fine together as long as you have full sun. If your soil is very rich, simply omit extra fertilizer for the cosmos. Most annuals, including all these, do well in a well-prepared garden soil of at least average fertility, need about an inch or so of water a week from you or the sky, and appreciate a few inches of organic mulch. While cosmos will tolerate lean dry soil and will grow more foliage and fewer blooms in very rich soil or with excess nitrogen, it is usually happy in average flower beds.
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