Answer: Hardy hibiscus (Hibiscus syriacus, Rose of Sharon) is very cold tolerant and should be planted as soon as possible. If you have purchased a bare-root shrub, it should be planted right away so it can awaken from dormancy as the season progresses. (Be sure to follow the instructions that came with it.) If you have a container grown plant, it too should be planted right away so the roots can begin to establish themselves now during the cooler weather.
If you have a tropical hibiscus (Hibiscus chinensis), however, you will need to wait until all danger of frost is past because these plants do not tolerate any frost at all. These plants are often maintained as container plants so they can be brought indoors at the end of the season to be enjoyed as houseplants. Good luck with your hibiscus!
Since you are new to gardening, you might want to look at some basic gardening books for help figuring out how to do things. One I particularly like is Gardening for Dummies by Michael MacCaskey ISBN 1-56884-644-4.
Enjoy your hibiscus!
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