Answer: You can take your geraniums indoors for the winter, or if space is a problem, simply take cuttings from your plants and grow them indoors. By next spring they will be good sized plants.
You can allow the flowers of your zinnias and marigolds to develop into seed pods then harvest the pods, break them open and spread the seeds on papertowels for a few days. Once the seeds are dry you can store them in an airtight container in a cool, dark place for planting next spring.
There aren't too many shade loving groundcovers, but you might try vinca minor or bishop's weed. Both spread quickly.
Best wishes with your garden!
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