When people ask about urban planter box freezing temperatures, the short answer is yes: an urban planter box can survive if it is left outside, but it will not happen automatically. The container itself may come through winter well if it is made from a frost-proof material, has proper planter box drainage, and is positioned to reduce freeze-thaw stress. The plants inside are a separate question. Hardy perennials, shrubs, and small trees may survive in a protected container, while tender annuals, tropical plants, and plants with shallow roots are much more likely to be damaged or killed by cold.
The biggest risk to the box is not just cold air; it is water. When soil stays wet and then freezes, it expands, and that pressure can crack ceramic, terracotta, thin plastic, and some concrete or stone planters. Wood can warp or rot, and metal can rust or split at seams. A frost-proof planter box should have drainage holes, be raised slightly off the ground, and allow excess water to escape freely. Avoid letting the box sit in a puddle or against a downspout. If the planter is decorative and not frost-proof, empty it or move it into a shed, garage, or sheltered spot before the first hard freeze.
For winter planter care, focus on both the container and the root zone. Insulate the outside of the planter with burlap, bubble wrap, or a layer of straw, and mulch the soil surface after the ground cools. Group pots together and place them against a wall or in a windbreak to reduce wind chill and sudden temperature swings. Snow can actually help insulate plants, but ice should not be allowed to seal the drainage holes. Do not fertilize in winter, and water sparingly only when the soil is dry and temperatures are above freezing.
Container plant winter protection depends on plant hardiness. A plant rated for your growing zone may still struggle in a container because roots are above ground and exposed to colder temperatures than they would be in the garden. Choose shrubs and perennials that are at least one or two zones hardier, or treat the planter as seasonal and replant with cold-tolerant pansies, evergreens, or ornamental cabbages. If you want the planter to survive year after year, combine a frost-proof planter box with good drainage, hardy plants, and a sheltered location. With those steps, an urban planter box can survive freezing temperatures outside; without them, the box or its plants may not make it through winter.