Answer: This plant is winter hardy outdoors only in very warm climates such as Florida or southern California. In Iowa, you will need to bring it indoors for the winter and then either keep it actively growing as a houseplant, or allow it to rest in a cool place. During fall and spring, you may want to set it outside during the day and bring it in at night to try to extend the growing season as long as possible. Do not panic if it defoliates when moved inside, this is fairly normal.
To keep it growing it will need at least six hours of strong direct sun at a cool room temperature of about 60 to 65 degrees. Bring it inside before temperatures drop below the mid 50's. Water sparingly as overwatering can cause the roots to rot. It is a cyclical bloomer so look for periods of vegetative growth alternating with blooming. If you need to prune, do so right after a blooming spell. If you see it become leggy during the winter, you may want to add a grow light for it and also trim it back as needed in late winter.
If you opt to keep it resting, leave it outdoors a little longer until temperatures are in the mid forties so it stops growing, then store where the temperature is cool but above freezing, the temperature should be about 40 to 45 degrees. Trim it back when you bring it indoors. Water just enough to keep the soil from going bone dry. In spring, as the weather moderates, gradually acclimate it to being outside again. Resume watering and fertilizing as it begins to grow again.
Be sure to loosen any ties along the stake as it grows so they do not damage the bark.
Good luck with your bougainvillea!
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