In most cases, no. A fire escape is part of the building’s emergency exit system, not extra balcony or storage space. Even a small urban planter box can create a trip hazard, block access to a ladder or window, add weight the structure was not designed for, or make it harder for firefighters and residents to move quickly. Fire codes commonly require fire escapes to stay clear and usable at all times, and many leases and building rules ban items on them. If you place one without permission, you could face a fine, have it removed, violate your lease, or create liability if someone is injured.
Before you buy or install anything, ask your landlord or property manager and your local fire department or building-code office. Get written approval, and follow any limits on size, weight, materials, and securing method. Use noncombustible containers and make sure nothing blocks the path of travel, ladders, windows, or exits.
Better options include a balcony or patio if your lease allows it, a properly mounted window box that does not interfere with escape routes, indoor planters, a community garden, or ground-level container gardening. If you are ever unsure, keep the fire escape completely clear—your safety and your neighbors’ safety matter more than the planter. This is general information, not legal advice.