Answer: It's great to be prepared! Your garage sounds like an ideal location to overwinter your plants, so long as you don't warm your car up in the garage and fill it with exhaust. In order to blossom and grow properly, strawberries and blueberries need winter chilling (several weeks of temps consistenly between 33 and 45F), so hopefully your garage can provide this. You shouldn't have to water too much over the winter, but just make sure the soil in the planters doesn't dry out completely. Move your geraniums and any frost-tender herbs in first, before fall frosts hit. Gradually acclimate them to the new environment by first moving them from sun, to dappled shade, and eventually to full shade over the course of a week or 10 days. At the same time, gradually decrease watering. Trim these plants back before taking them inside. The roses and berries can stay out through frost, as it will allow them to enter dormancy. After they drop their leaves and before it gets so cold that the soil freezes, you can move them indoors. Decrease watering, but don't let the soil dry, before bringing them indoors.
If you have room in your house and a brightly lit location, you can overwinter your geraniums and roses as houseplants, too, though they may get buggy. You don't mention what kind of herbs you have, but rosemary can also be treated as a houseplant. Lavender should be pruned back after a frost or two before spending the winter in the garage. In the spring, you can cut the dead leaves from the strawberry plants as new growth starts. Place the blueberries, roses, and strawberries outside, reversing the gradual acclimation process, as nights stay consistently above freezing. You can start getting your tender plants acclimated shortly after that, but don't leave them out if night frost is predicted. I hope this helps you keep your potted garden perpetually!
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