Answer: If the plants are acclimated to being outside it is best to keep them outside in the sunshine. If you aren't sure, begin acclimating them by setting them outside in a protected sunny spot and eventually moving them to their permanent spot. Cover them at night at first if the temperatures are supposed to drop. Strawberry plants are very cold hardy once acclimated. The spring freeze warnings for strawberries are to protect the blossoms (and thus the fruit) rather than the plants themselves. If your plants have blossoms, you might want to cover them on colder nights even after they are acclimated. It also occurs to me that if your jar is truly terra cotta, you may want to protect it from freezing as well. An upended cardboard box or trash can should do the trick unless it is very cold.
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