If the planter is structurally sound, treat it as a frame rather than a mistake. First, decide what you want to see: a green screen, a bench, a sculpture, or simply a cleaner edge. For a quick camouflage, wrap the box in reed fencing, bamboo roll, or weather-resistant slatted panels. Attach them to a separate inner frame or use outdoor zip ties, and leave gaps at the bottom for drainage and airflow. If you can paint or stain it, choose a color that matches your railing, wall, or paving; matte charcoal or deep green often disappears better than glossy bright colors.
Next, use plants to soften the shape. Place a trellis behind or inside the box and grow climbing plants such as ivy, clematis, or jasmine, depending on light. Add tall grasses or ferns around the base to blur hard lines. Group smaller pots in front so the eye reads a layered garden rather than one ugly container. A freestanding privacy screen, outdoor bench, or bike rack placed slightly in front can also hide the box while making the space more useful.
For a more polished look, build a simple slatted wood or metal cover that sits over the box like a sleeve, but do not seal it completely. Keep access to irrigation, drainage holes, and any utility covers. Battery-powered outdoor lights or a small uplight can shift attention at night, and a shallow tray on top can turn the planter into a side table if the plants allow. Check rental, HOA, or building rules before attaching anything. The goal is not to pretend the planter does not exist; it is to make it look deliberate, tidy, and part of the design.