Yes—urban planter box covers do exist for winter protection, and they are increasingly common in cities where containers face wind, salt, snow, and freeze-thaw cycles. They range from simple DIY frames wrapped in fleece to ready-made zip-up covers, rigid cloches, insulated wraps, and custom-fit panels for rectangular or modular planters.
For urban settings, choose covers designed for wind and tight spaces. Look for UV-stabilized, breathable fabrics or vented polyethylene; tie-downs, weighted hems, or ground stakes; reinforced seams; and easy access for watering and inspection. Breathability matters because airtight plastic can trap condensation and cause rot or mold. Rigid covers or hoops keep fabric off leaves and support snow loads.
Cover type depends on plants and exposure. Frost fleece suits hardy perennials, herbs, and small shrubs. Insulated covers help tender evergreens in exposed balcony planters. Rigid mini-greenhouses or cloches work for winter greens but need venting on sunny days. For large built-in planter boxes, custom canvas covers with zippered panels are practical and less visibly intrusive.
Do not seal urban planters completely. Winter sun on a covered box can overheat plants, especially near buildings and dark paving. Open vents on mild days, remove covers during warm spells, and check soil moisture—covered containers still dry out and may need occasional watering. Reduce watering but avoid bone-dry soil. Mulch before covering and avoid covering wet foliage. Secure covers against strong city winds and keep them clear of drainage holes.
In short, urban planter box covers are available and useful when they are breathable, vented, securely fitted, and used with seasonal monitoring. They are not set-and-forget wraps; the best winter protection balances wind and frost control with airflow, drainage, and access.