Yes, you can attach urban planter boxes directly to your railing, but safety and method are paramount. First, check your railing's material and weight capacity. Metal railings are typically strongest. Never exceed the railing's load limit, considering wet soil and plant weight.
The safest method is using specially designed railing planter brackets or cradles that hook over the top and secure underneath. For a more permanent fix, use UV-resistant straps or heavy-duty zip ties for lightweight boxes, ensuring they are tight and checked regularly. For wooden railings, you can screw mounting blocks to the railing posts (not the top cap) and then attach the planter box to the blocks. Avoid drilling directly into thin metal or weakening the railing's structure.
Always use a lightweight potting mix to reduce weight and ensure your planter has adequate drainage holes. With the right secure attachment, you can transform your railing into a vibrant, green space.