Yes, in most cases you can leave an urban planter box empty over winter without automatically ruining it. The real question is what “empty” means and what the planter is made of. If it is truly empty—no soil and no plants—and has good drainage, it is likely to survive winter well. If it still holds soil, that soil can absorb rain or snowmelt and expand when it freezes, putting pressure on the sides and causing cracks, bowing, or separated joints.
Material matters. Wood can warp, dry-crack, or rot if it stays wet. Metal can rust at seams and scratches. Ceramic and terracotta are vulnerable to freeze-thaw cracking, especially if they are glazed only on one side or have no drainage. Composite and plastic are more forgiving, but they can still fade, become brittle, or blow over in strong wind.
To protect an empty urban planter over winter, tip it slightly if possible so water drains out, or place it under a sheltered overhang. Clean out old roots and debris so pests do not move in. Check the drainage holes and clear them. If the planter is light, move it to a protected corner or store it in a shed or garage. If it must stay outside, raise it off freezing pavement, avoid sealing it airtight, and secure it against wind. For ceramic pots, bring them indoors if you can; if not, keep them dry and covered. For wood, a fresh coat of oil or sealant before winter helps. For metal, touch up chips to limit rust.
Do not fill an empty planter with water or leave a saucer full of ice. Also avoid covering it with a tight plastic sheet that traps moisture. A breathable cover or a tilted, drained pot is better. In spring, inspect for cracks, loose joints, rust, or warped sides before refilling.
So the short answer is: yes, you can leave it empty, but it can still be damaged by moisture, freezing, UV, and wind. A little prep—drainage, cleaning, shelter, and material-specific protection—will greatly reduce the risk.